Chapter 3. Linux Commands

When tracing calls with the -t option, report calls made during initialization.

-i, --initialization

-o file, --output=file

Save output to file.

-t macro, --trace=macro

Report the list of calls to macro.

-v, --verbose

Verbosely print information about the progress of autoconf.

-I dir, --include=dir

Search in directory dir for input files.

-V, --version

Print any warnings related to category. Accepted categories are:

-W category, --warnings=category

cross: Cross compilation.
obsolete: Obsolete constructs.
syntax: Questionable syntax.
all: All warnings.
no-category: Turn off warnings for category.
none: Turn off all warnings.
error: Treat warnings as errors.

autoheader

autoheader [options] [template_file]

GNU autoconf tool. Generate a template file of C #define statements from m4 macros defined in template_file, if given, or in a configue.ac or configure.in file in the current working directory. The generated template file is almost invariably called config.h.in.

Options

-d, --debug

Don't remove temporary files.

-f, --force

Replace files generated previously by autoheader.

-h, --help

Verbosely print information about the progress of autoheader.

-o file, --output=file

Save output to file.

-v, --verbose

-I dir, --include=dir

Search in directory dir for input files.

-V, --version

Print any warnings related to category. Accepted categories are:

-W category, --warnings=category

obsolete: Obsolete constructs.
all: All warnings.
no-category: Turn off warnings for category.
none: Turn off all warnings.
error: Treat warnings as errors.

automake

automake [options] [template_file]

GNU automake tool. Creates GNU standards-compliant Makefile.in files from Makefile.am template files and can be used to ensure that projects contain all files and install options required to be standards-compliant. Note that Versions 1.4 and 1.6 differ enough that many distributions include an automake14 package for backward compatibility.

Options

-a, --add-missing: Add any missing files automake requires to the directory by creating symbolic links to automake's default versions.
-c, --copy: Used with the -a option. Copy missing files instead of creating symbolic links.
--cygnus: Specifies project has a Cygnus-style source tree.
-f, --force-missing: Used with the -a option. Replace required files even if a local copy already exists.
--foreign: Treat project as a non-GNU project. Check only for elements required for proper operation.
--gnu: Treat project as a GNU project with the GNU project structure.
--gnits: A stricter version of --gnu, performing more checks to comply with GNU project structure rules.
--help: Print help message, then exit.
-i, --ignore-deps: Disable automatic dependency tracking.
--libdir=dir: Used with the -a option. Search in directory dir for default files.
--no-force: Update only Makefile.in files that have updated dependents.
-v, --verbose: List files being read or created by automake.
--version: Print version number, then exit.
-Werror: Treat warnings as errors.

autoreconf

autoreconf [options]

GNU autoconf tool. Update configure scripts by running autoconf, autoheader, aclocal, automake, and libtoolize in specified directories and subdirectories. This command is seldom invoked manually. It is usually called automatically from other autoconf tools.

Options

-d, --debug

Don't remove temporary files.

-f, --force

Remake all configure scripts, even when newer than their template files.

-h, --help

Add any default files missing from package by copying versions included with autoconf and automake.

-i, --install

-s, --symlink

Used with the -i option. Create symbolic links to default files instead of copying them.

-v, --verbose

Verbosely print information about the progress of autoreconf.

-I dir, --include=dir

Search in directory dir for input files.

-V, --version

Print any warnings related to category. Accepted categories are:

-W category, --warnings=category

cross: Cross compilation.
obsolete: Obsolete constructs.
syntax: Questionable syntax.
all: All warnings.
no-category: Turn off warnings for category.
none: Turn off all warnings.
error: Treat warnings as errors.

autoscan

autoscan [options] [directory]

GNU autoconf tool. Create or maintain a preliminary configure.ac file named configure.scan based on source files in specified directory, or current directory if none given. If a configure.ac file already exists, autoconf will check it for completeness and print suggestions for correcting any problems it finds.

Options

-d, --debug: Don't remove temporary files.
-h, --help: Print help message, then exit.
-v, --verbose: Verbosely print information about the progress of autoscan.
-I dir, --include=dir: Search in directory dir for input files. Use multiple times to add multiple directories.
-B dir, --prepend-include=dir: Search dir for input files before searching in other directories. Use multiple times to add multiple directories.
-V, --version: Print version number, then exit.

autoupdate

autoupdate [options] [file]

GNU autoconf tool. Update the configure template file file, or configure.ac if no file is specified. This command is seldom invoked manually. It is usually called automatically from other autoconf tools.

Options

-d, --debug: Don't remove temporary files.
-f, --force: Remake all configure scripts, even when newer than their template files.
-h, --help: Print help message, then exit.
-v, --verbose: Verbosely print information about the progress of autoupdate.
-I dir, --include=dir: Search in directory dir for input files.
-V, --version: Print version number, then exit.

badblocks

badblocks [options] device block-count

System administration command. Search device for bad blocks. You must specify the number of blocks on the device (block-count).

Options

-b blocksize: Expect blocksize-byte blocks.
-c blocksize: Test blocksize-byte blocks at a time. Default is 16.
-f: Force a read/write or nondestructive write test on a mounted device. Use only when /etc/mtab incorrectly reports a device as mounted.
-i file: Skip test of known bad blocks listed in file.
-n: Perform a nondestructive test by writing to each block and then reading back from it while preserving data.
-o file: Direct output to file.
-p number: Repeat search of device until no new bad blocks have been found in number passes. Default is 0.
-v: Verbose mode.
-w: Test by writing to each block and then reading back from it.

banner

banner [option] [characters]

Print characters as a poster. If no characters are supplied, banner prompts for them and reads an input line from standard input. By default, the results go to standard output, but they are intended to be sent to a printer.

Option

-w width: Set width to width characters. Note that if your banner is in all lowercase, it will be narrower than width characters. If -w is not specified, the default width is 132. If -w is specified but width is not provided, the default is 80.

Example

/usr/games/banner -w50 Happy Birthday! |lpr

basename

basename name [suffix]
basename option

Remove leading directory components from a path. If suffix is given, remove that also. The result is printed to standard output.

Options

--help: Print help message and then exit.
--version: Print the version number and then exit.

Examples

 basename /usr/lib/libm.a
libm.a

% basename /usr/lib/libm.a .a
libm

bash

bash [options] [file [arguments]]
sh [options] [file [arguments]]

Standard Linux shell, a command interpreter into which all other commands are entered. For more information, see Chapter 7.

batch

batch [options] [time]

Execute commands entered on standard input. If time is omitted, execute commands when the system load permits (when the load average falls below 0.8). Very similar to at, but does not insist that the execution time be entered on the command line. See at for details.

Options

-f file: Read job from file, not standard input.
-m: Mail user when job has completed, regardless of whether output was created.
-q letter: Place job in queue denoted by letter, where letter is one letter from a-z or A-Z. The default queue is b. (The at queue defaults to a.) Higher-lettered queues run at a lower priority.
-V: Print the version number and then exit.
-v: Display the time a job will be executed.

bc [options] [files]

bc is a language (and compiler) whose syntax resembles that of C, but with unlimited-precision arithmetic. bc consists of identifiers, keywords, and symbols, which are briefly described in the following entries. Examples are given at the end.

Interactively perform arbitrary-precision arithmetic or convert numbers from one base to another. Input can be taken from files or read from the standard input. To exit, type quit or EOF.

Options

-h, --help: Print help message and exit.
-i, --interactive: Interactive mode.
-l, --mathlib: Make functions from the math library available.
-s, --standard: Ignore all extensions, and process exactly as in POSIX.
-w, --warn: When extensions to POSIX bc are used, print a warning.
-q, --quiet: Do not display welcome message.
-v, --version: Print version number.

Identifiers

An identifier is a series of one or more characters. It must begin with a lowercase letter but may also contain digits and underscores. No uppercase letters are allowed. Identifiers are used as names for variables, arrays, and functions. Variables normally store arbitrary-precision numbers. Within the same program you may name a variable, an array, and a function using the same letter. The following identifiers would not conflict:

x: Variable x.
x[i]: Element i of array x. i can range from 0 to 2047 and can also be an expression.
x(y,z): Call function x with parameters y and z.

Input-output keywords

ibase, obase, scale, and last store a value. Typing them on a line by themselves displays their current value. You can also change their values through assignment. The letters A-F are treated as digits whose values are 10-15.

ibase = n: Numbers that are input (e.g., typed) are read as base n (default is 10).
obase = n: Numbers that are displayed are in base n (default is 10). Note: once ibase has been changed from 10, use A to restore ibase or obase to decimal.
scale = n: Display computations using n decimal places (default is 0, meaning that results are truncated to integers). scale is normally used only for base-10 computations.
last: Value of last printed number.

Statement keywords

A semicolon or a newline separates one statement from another. Curly braces are needed when grouping multiple statements.

if (rel-expr) {statements} [else {statements}]

Do one or more statements if relational expression rel-expr is true. Otherwise, do nothing, or if else (an extension) is specified, do alternative statements. For example:

if (x=  =y) {i = i + 1} else {i = i - 1}

while (rel-expr) {statements}

Repeat one or more statements while rel-expr is true; for example:

while (i>0) {p = p*n; q = a/b; i = i-1}

for (expr1; rel-expr; expr2) {statements}

for (i=1; i<=10; i++) i*5

GNU bc does not require three arguments to for. A missing argument 1 or 3 means that those expressions will never be evaluated. A missing argument 2 evaluates to the value 1.

break

Terminate a while or for statement.

print list

GNU extension. It provides an alternate means of output. list consists of a series of comma-separated strings and expressions; print displays these entities in the order of the list. It does not print a newline when it terminates. Expressions are evaluated, printed, and assigned to the special variable last. Strings (which may contain special characters, i.e., characters beginning with \) are simply printed. Special characters can be:

a: Alert or bell
b: Backspace
f: Form feed
n: Newline
r: Carriage return
q: Double quote
t: Tab
\: Backslash

continue

GNU extension. When within a for statement, jump to the next iteration.

halt

GNU extension. Cause the bc processor to quit when executed.

quit

GNU extension. Cause the bc processor to quit whether line is executed or not.

limits

GNU extension. Print the limits enforced by the local version of bc.

Function keywords

define f(args) {: Begin the definition of function f having the arguments args. The arguments are separated by commas. Statements follow on successive lines. End with }.
auto x, y: Set up x and y as variables local to a function definition, initialized to 0 and meaningless outside the function. Must appear first.
return(expr): Pass the value of expression expr back to the program. Return 0 if (expr) is left off. Used in function definitions.
sqrt(expr): Compute the square root of expression expr.
length(expr): Compute how many significant digits are in expr.
scale(expr): Same as length, but count only digits to the right of the decimal point.
read( ): GNU extension. Read a number from standard input. Return value is the number read, converted via the value of ibase.

Math library functions

These are available when bc is invoked with -l. Library functions set scale to 20.

s(angle): Compute the sine of angle, a constant or expression in radians.
c(angle): Compute the cosine of angle, a constant or expression in radians.
a(n): Compute the arctangent of n, returning an angle in radians.
e(expr): Compute e to the power of expr.
l(expr): Compute the natural log of expr.
j(n, x): Compute the Bessel function of integer order n.

Operators

These consist of operators and other symbols. Operators can be arithmetic, unary, assignment, or relational:

arithmetic: + - * / % ^
unary: - ++ --
assignment: =+ =- =* =/ =% =^ =
relational: < <= > >= = = !=

Other symbols

/* */: Enclose comments.
( ): Control the evaluation of expressions (change precedence). Can also be used around assignment statements to force the result to print.
{ }: Use to group statements.
[ ]: Indicate array index.
"text": Use as a statement to print text.

Examples

Note in these examples that when you type some quantity (a number or expression), it is evaluated and printed, but assignment statements produce no display.

ibase = 8       Octal input
20              Evaluate this octal number
16              Terminal displays decimal value
obase = 2       Display output in base 2 instead of base 10
20              Octal input
10000           Terminal now displays binary value
ibase = A       Restore base-10 input
scale = 3       Truncate results to 3 decimal places
8/7             Evaluate a division
1.001001000     Oops!  Forgot to reset output base to 10
obase=10        Input is decimal now, so A isn't needed
8/7
1.142           Terminal displays result (truncated)

The following lines show the use of functions:

define p(r,n){  Function p uses two arguments
auto v          v is a local variable
v = r^n         r raised to the n power
return(v)}      Value returned

scale=5
x=p(2.5,2)      x = 2.5 ^ 2
x               Print value of x
6.25
length(x)       Number of digits
3
scale(x)        Number of places right of decimal point
2

biff

biff [arguments]

Notify user of mail arrival and sender's name. biff operates asynchronously. Mail notification works only if your system is running the comsat(8) server. The command biff y enables notification, and the command biff n disables notification. With no arguments, biff reports biff's current status.

bison

bison [options] file

Given a file containing context-free grammar, convert into tables for subsequent parsing while sending output to file.c. This utility is to a large extent compatible with yacc, and in fact is named for it. All input files should use the suffix .y; output files will use the original prefix. All long options (those preceded by --) may instead be preceded by +.

Options

-b prefix, --file-prefix=prefix: Use prefix for all output files.
-d, --defines: Generate file.h, producing #define statements that relate bison's token codes to the token names declared by the user.
-r, --raw: Use bison token numbers, not yacc-compatible translations, in file.h.
-k, --token-table: Include token names and values of YYNTOKENS, YYNNTS, YYNRULES, and YYNSTATES in file.c.
-l, --no-lines: Exclude #line constructs from code produced in file.c. (Use after debugging is complete.)
-n, --no-parser: Suppress parser code in output, allowing only declarations. Assemble all translations into a switch statement body and print it to file.act.
-o file, --output-file=file: Output to file.
-p prefix, --name-prefix=prefix: Substitute prefix for yy in all external symbols.
-t, --debug: Compile runtime debugging code.
-v, --verbose: Verbose mode. Print diagnostics and notes about parsing tables to file.output.
-V, --version: Display version number.
-y, --yacc, --fixed-output-files: Duplicate yacc's conventions for naming output files.

bootpd

bootpd [options] [configfile [dumpfile]]

TCP/IP command. Internet Boot Protocol server. bootpd normally is run by /etc/inetd by including the following line in the file /etc/inetd.conf:

bootps dgram udp wait root /etc/bootpd bootpd

This causes bootpd to be started only when a boot request arrives. It may also be started in standalone mode, from the command line. Upon startup, bootpd first reads its configuration file, /etc/bootptab (or the configfile listed on the command line), then begins listening for BOOTREQUEST packets.

bootpd looks in /etc/services to find the port numbers it should use. Two entries are extracted: bootps (the bootp server listening port) and bootpc (the destination port used to reply to clients).

If bootpd is compiled with the -DDEBUG option, receipt of a SIGUSR1 signal causes it to dump its memory-resident database to the file /etc/bootpd.dump or the dumpfile specified on the command line.

Options

-c directory: Force bootpd to work in directory.
-d level: Specify the debugging level. Omitting level will increment the level by 1.
-t timeout: Specify a timeout value in minutes. A timeout value of 0 means wait forever.

Configuration file

The bootpd configuration file has a format in which two-character, case-sensitive tag symbols are used to represent host parameters. These parameter declarations are separated by colons. The general format is:

hostname:tg=value:tg=value:tg=value

where hostname is the name of a bootp client and tg is a tag symbol. The currently recognized tags are listed in the following section.

Options

-f file: Read the boot filename from file.
-h: Identify client by hardware address, not IP address.
-m magic-number: Provide magic-number as the first word of the vendor options field.

bzcmp

bzcmp [options] file1 file2

Apply cmp to the data from files in the bzip2 format without requiring on-disk decompression. See bzip2 and cmp for usage.

bzdiff

bzdiff [options] file1 file2

Apply diff to data from files in the bzip2 format without requiring on-disk decompression. See bzip2 and cmp for usage.

bzgrep

bzgrep [options] pattern [file...]

Apply grep to data from files in the bzip2 format without requiring on-disk decompression. See bzip2 and grep for usage.

bzip2

bzip2 [options] filenames
bunzip2 [options] filenames
bzcat [option] filenames
bzip2recover filenames

File compression and decompression utility similar to gzip, but uses a different algorithm and encoding method to get better compression. bzip2 replaces each file in filenames with a compressed version of the file and with a .bz2 extension appended. bunzip2 decompresses each file compressed by bzip2 (ignoring other files, except to print a warning). bzcat decompresses all specified files to standard output, and bzip2recover is used to try to recover data from damaged files.

Additional related commands include bzcmp, which compares the contents of bzipped files; bzdiff, which creates diff (difference) files from a pair of bzip files; bzgrep, to search them; and the bzless and bzmore commands, which apply the more and less commands to bzip output as bzcat does with the cat command. See cat, cmp, diff, and grep for information on how to use those commands.

Options

--: End of options; treat all subsequent arguments as filenames.
-dig: Set block size to dig × 100KB when compressing, where dig is a single digit from 1 to 9.
-c, --stdout: Compress or decompress to standard output.
-d, --decompress: Force decompression.
-f, --force: Force overwrite of output files. Default is not to overwrite. Also forces breaking of hard links to files.
-k, --keep: Keep input files; don't delete them.
-L, --license, -V, --version: Print license and version information and exit.
-q, --quiet: Print only critical messages.
-s, --small: Use less memory, at the expense of speed.
-t, --test: Check the integrity of the files, but don't actually compress them.
-v, --verbose: Verbose mode. Show the compression ratio for each file processed. Add more -v's to increase the verbosity.
-z, --compress: Force compression, even if invoked as bunzip2 or bzcat.
--repetitive-fast, --repetitive-best: Sometimes useful in versions earlier than 0.9.5 (which has an improved sorting algorithm) for providing some control over the algorithm.

bzless

bzless [options] file

Applies less to data files in the bzip2 format without requiring on-disk decompression. See bzip2 and less for usage.

bzmore

bzmore [options] file

Applies more to data files in the bzip2 format without requiring on-disk decompression. See bzip2 and more for usage.

c++

c++ [options] files

See g++.

c++filt

c++filt [options] [symbol]

Decode the specified C++ or Java function name symbol, or read and decode symbols from standard input if no symbol is given. This command reverses the name mangling used by C++ and Java compilers to support function overloading, multiple functions that share the same name.

Options

-_, --strip-underscores

Remove initial underscores from symbol names.

--help

Print usage information, then exit.

-j, --java

Print names using Java syntax.

-n, --no-strip-underscores

Preserve initial underscores on symbol names.

-s format, --format=format

Expect symbols to have been coded in the specified format. Format may be one of the following:

arm: C++ Annotated Reference Manual.
edg: EDG (Intel) compiler.
gnu: Gnu compiler (the default).
gnu-new-abi: Gnu compiler with the new application binary interface (for gcc 3.x.)
hp: HP compiler.
lucid: Lucid compiler.

--version

System administration command. Control PCMCIA sockets or select the current scheme. The current scheme is sent along with the address of any inserted cards to configuration scripts (by default located in /etc/pcmcia). The scheme command displays or changes the scheme. The other commands operate on a named card socket number, or all sockets if no number is given.

cal

cal [options] [[month] year]

Print a 12-month calendar (beginning with January) for the given year, or a one-month calendar of the given month and year. month ranges from 1 to 12. year ranges from 1 to 9999. With no arguments, print a calendar for the current month.

Options

-j: Display Julian dates (days numbered 1 to 365, starting from January 1).
-m: Display Monday as the first day of the week.
-y: Display entire year.

Examples

cal 12 1995
cal 1994 > year_file

cardctl

cardctl [options] command

Commands

config [socket]: Display current socket configuration.
eject [socket]: Prepare the system for the card(s) to be ejected.
ident [socket]: Display card identification information.
insert [socket]: Notify system that a card has been inserted.
reset [socket]: Send reset signal to card.
resume [socket]: Restore power to socket and reconfigure for use.
scheme [name]: Display current scheme or change to specified scheme name.
status [socket]: Display current socket status.
suspend [socket]: Shut down device and cut power to socket.

Options

-c directory: Look for card configuration information in directory instead of /etc/pcmcia.
-f file: Use file to keep track of the current scheme instead of /var/run/pcmcia-scheme.
-s file: Look for current socket information in file instead of /var/run/stab.

cardmgr

cardmgr [options]

System administration command. The PCMCIA card daemon. cardmgr monitors PCMCIA sockets for devices that have been added or removed. When a card is detected, it attempts to get the card's ID and configure it according to the card configuration database (usually stored in /etc/pcmcia/config). By default, cardmgr does two things when it detects a card: it creates a system log entry and it beeps. Two high beeps mean it successfully identified and configured a device. One high beep followed by one low beep means it identified the device, but was unable to configure it successfully. One low beep means it could not identify the inserted card. Information on the currently configured cards can be found in /var/run/stab.

Options

-c directory: Look for the card configuration database in directory instead of /etc/pcmcia.
-d: Use modprobe instead of insmod to load the PCMCIA device driver.
-f: Run in the foreground to process the current cards, then run as a daemon.
-m directory: Look in directory for card device modules. Default is /lib/modules/RELEASE, where RELEASE is the current kernel release.
-o: Configure the cards present in one pass, then exit.
-pfile: Write cardmgr's process ID to file instead of /var/run/cardmgr.pid.
-q: Run in quiet mode. No beeps.
-s file: Write current socket information to file instead of /var/run/stab.
-v: Verbose mode.
-V: Print version number and exit.

cat

cat [options] [files]

Read (concatenate) one or more files and print them on standard output. Read standard input if no files are specified or if - is specified as one of the files; input ends with EOF. You can use the > operator to combine several files into a new file or >> to append files to an existing file.

Options

-A, --show-all: Same as -vET.
-b, --number-nonblank: Number all nonblank output lines, starting with 1.
-e: Same as -vE.
-E, --show-ends: Print $ at the end of each line.
-n, --number: Number all output lines, starting with 1.
-s, --squeeze-blank: Squeeze down multiple blank lines to one blank line.
-t: Same as -vT.
-T, --show-tabs: Print TAB characters as ^I.
-u: Ignored; retained for Unix compatibility.
-v, --show-nonprinting: Display control and nonprinting characters, with the exception of LINEFEED and TAB.

Examples

cat ch1               Display a file
cat ch1 ch2 ch3 > all Combine files
cat note5 >> notes    Append to a file
cat > temp1           Create file at terminal; end with EOF
cat > temp2 << STOP   Create file at terminal; end with STOP

cc [options] files

See gcc.

cdda2wav

cdda2wav [options] [output.wav]

Convert Compact Disc Digital Audio (CDDA) to the WAV format. This process is often called "ripping" a CD-ROM, and is generally performed before using an encoder to convert the file to a compressed music format such as OGG or MP3. By default, cdda2wav reads data from the /dev/cdrom device and outputs one WAV file per track.

Options

Some of the following options use sectors as a unit of measurement. Each sector of data on a CD represents approximately 1/75 second of play time.

-D, --device devicename: Specify the device. The device must work with the -i (--interface) settings.
-A , --auxdevice drivename: Specify a different drive for ioctl purposes.
-I, --interface ifname: Specify the type of interface. For Linux systems, the most appropriate value is usually cooked_ioctl.
-s, --stereo: Record in stereo. Use -m (--mono) to record in mono.
-x, --max: Set recording quality (and amount of hard disk usage) to maximum.
-b, --bits-per-sample n: Set the quality of samples to n bits per sample per channel. Possible values are 8, 12, and 16.
-r, --rate n: Set the sample rate in samples per second. To get a list of possible values, use the -R option.
-R, --dump-rates: Output a list of possible sample rates and dividers. This option is typically used alone.
-P, --set-overlap n: Use n sectors of overlap for jitter correction.
-n, --sectors-per-request n: Read n sectors in each request.
-t, --track tracknumber: Set start track and, optionally, end track. Separate the tracks with the + character.
-i, --index n: Set the start index to n when recording.
-o, --offset n: Start recording n sectors before the beginning of the first track.
-O, --output-format: Choose the output file format. Normal file options are wav, aiff, aifc, au, and sun. You can also use cdr and raw for headerless files dumped into recording devices.
-d, --duration: Set to a number followed by f for frames (sectors) or s for seconds. Set time to zero to record an entire track. For example, to copy two minutes, enter 120s.
-B, --bulk: Copy each track into its own file.
-w, --wait: Wait for a signal before recording anything.
-e, --echo: Copy audio data to a sound device rather than to a file.
-p, --set-pitch n: Adjust the pitch by n percent when copying data to an audio device.
-S, --speed-select n: Specify the speed at which your system will read the CD-ROM. Set the value to the multiple of normal playback speed given as your CD-ROM drive speed (4, 16, 32, and so forth). Setting the speed lower than the maximum can prevent errors in some cases.
-q, --quiet: Quiet mode; the program will not send any data to the screen.
-J, --version: Display version and quit.

Examples

For most systems, you should be able to copy a complete CD to a single WAV file with the following command:

cdda2wav

To copy a complete CD to a set of WAV files, one per track:

cdda2wav -B

cdparanoia

cdparanoia [options] span [outfile]

Like cdda2wav, cdparanoia records Compact Disc audio files as WAV, AIFF, AIFF-C, or raw format files. It uses additional data-verification and sound-improvement algorithms to make the process more reliable, and is used by a number of graphical recording programs as a backend.

Options

-v, --verbose: Verbose mode.
-q, --quiet: Quiet mode.
-e, --stderr-progress: Send all progress messages to stderr instead of stdout; used by wrapper scripts.
-V, --version: Print version information and quit.
-Q, --query: Display CD-ROM table of contents and quit.
-s, --search-for-drive: Search for a drive, even if /dev/cdrom exists.
-h, --help: Display options and syntax.
-p, --output-raw: Output headerless raw data.
-r, --output-raw-little-endian: Output raw data in little-endian byte order.
-R, --output-raw-big-endian: Output raw data in big-endian byte order.
-w, --output-wav: Output in WAV format. This is the default.
-f, --output-aiff: Output in AIFF format.
-a, --output-aifc: Output in AIFF-C format.
-c, --force-cdrom-little-endian: Force cdparanoia to treat the drive as a little-endian device.
-C, --force-cdrom-big-endian: Force cdparanoia to treat the drive as a big-endian device.
-d, --force-cdrom-device devicename: Specify a device name to use instead of the first readable CD-ROM available.
-S, --force-read-speed n: Set the read speed to n on drives that support it. This is useful if you have a slow drive or are low on memory.
-Z, --disable-paranoia: Disable data verification and correction. Causes cdparanoia to behave exactly as cdda2wav would.
-z, --never-skip[=retries]: If a read fails (for example, due to a scratch in the disc), try again and again. If you specify a number, cdparanoia will try that number of times. If you do not, cdparanoia will retry until it succeeds.
-Y, --disable-extra-paranoia: Use data verification and correction only at read boundaries. Not recommended.
-X, --abort-on-skip: If a read fails and must be skipped, skip the entire track and delete any partially completed output file.

Progress symbols

The output during operation cdparanoia includes both smiley faces and more standard progress symbols. They are:

:-): Operation proceeding normally.
:-|: Operation proceeding normally, but with jitter during reads.
:-/: Read drift.
8-|: Repeated read problems in the same place.
:-O: SCSI/ATAPI transport error (hardware problem not related to the disc itself).
:-(: Scratch detected.
;-(: Unable to correct problem.
8-X: Unknown and uncorrectable error.
:^D: Finished.
: Blank space in the progress indicator means that no corrections were necessary.
-: Jitter correction was required.
+: Read errors.
!: Errors even after correction; repeated read errors.
e: Corrected transport errors.
V: An uncorrected error or a skipped read.

The span argument

The cdparanoia command takes exactly one argument, which describes how much of the CD to record. It uses numbers followed by bracketed times to designate track numbers and time within them. For example, the string 1[2:23]-2[5] indicates a recording from the two-minute and twenty-three-second mark of the first track up to the fifth second of the second track. The time format is demarcated by colons, hours:minutes:seconds:.sectors, with the last item, sectors, preceded by a decimal point (a sector is 1/75 of a second). It's best to put this argument within quotes.

If you use the -B option, the span argument is not required.

cdrdao

cdrdao command [options] toc-file

Write all content specified in description file toc-file to a CD-R disk drive in one step. This is called disk-at-once (DAO) mode, as opposed to the more commonly used track-at-once (TAO) mode. DAO mode allows you to change the length of gaps between tracks and define data to be written in these gaps (like hidden bonus tracks or track intros). The toc file can be created by hand or generated from an existing CD using cdrdao's read-toc command. A cue file, as generated by other audio programs, can be used instead of a toc file. The file format for toc files is discussed at length in the cdrdao manpage.

Commands

The first argument must be a command. Note that not all options are available for all commands.

show-toc: Print a summary of the CD to be created.
read-toc: Read from a CD and create a disk image and toc file that will allow creation of duplicates.
read-cddb: Check a CDDB server for data about the CD represented by a given toc file, then write that data to the toc file as CD-TEXT data.
show-data: Print out the data that will be written to the CD-R. Useful for checking byte order.
read-test: Check the validity of the audio files described in the toc file.
disk-info: Display information about the CD-R currently in the drive.
msinfo: Display multisession information. Useful mostly for wrapper scripts.
scanbus: Scan the system bus for devices.
simulate: A dry run: do everything except write the CD.
unlock: Unlock the recorder after a failure. Run this command if you cannot eject the CD after using cdrdao.
write: Write the CD.
copy: Copy the CD. If you use a single drive, you will be prompted to insert the CD-R after reading. An image file will be created unless you use the --on-the-fly flag and two CD drives.

Options

--device bus,id,logicalunit: Set the SCSI address of the CD-R using the bus number, ID number, and logical unit number.
--source-device bus,id,logicalunit: Used only with the copy command. Set the SCSI address of the source device.
--driver driver-id:option-flags: Force cdrdao to use the driver you choose with the driver options named, instead of the driver it autodetects.
--source-driver driver-id:option-flags: Used only with the copy command. Set the source device driver and flags.
speed value: Set the write speed to value. The default is the highest available; use a lower value if higher values give poor results.
--datafile filename: When used with the read-toc command, specifies the data file placed in the toc file. When used with read-cd and copy, specifies the name of the image file created.
read-raw: Used only with the read-cd command. Write raw data to the image file.
--buffers n: Set the number of seconds of data to be buffered. Default is 32; set to a higher number if your read source is unreliable or is slower than the CD-R.
--multi: Record as a multisession disc.
--overburn: If you are using a disc with more storage space than cdrdao detects, use this option to keep writing even when cdrdao thinks you're out of space.
--eject: Eject the disc when done.
--swap: Swap byte order for all samples.
--session n: Used only with the read-toc and read-cd commands when working with multisession CDs. Specifies the number of the session to be processed.
--reload: Allow the drive to be opened before writing without interrupting the process. Used with simulation runs.
--force: Override warnings and perform the action anyway.
--paranoia-mode n: Specifies n, from 0 to 3, for the amount of error correction in the CD read. 0 is none, 3 is full (see cdparanoia for information about error correction). Set error correction to a lower number to increase read speed. The default is 3.
--keepimage: Used only with the copy command. Keeps the image file created during the copy process.
--on-the-fly: Do not create an image file: pipe data directly from source to CD-R.
--with-cddb: Use CDDB to fetch information about the disc and save it as CD-TEXT data. Used with the copy, read-toc, and read-cd commands.
cddb-servers server,server: Enter hosts for servers. Servers may include ports, paths, and proxies; you can list multiple servers separated by spaces or commas.
--cddb-timeout s: Set the timeout for CDDB server connections to s seconds.
--cddb-directory localpath: CDDB data that is fetched will be saved in the directory localpath.
--save: Save current options to the settings file $HOME/.cdrdao.
-n: Do not wait 10 seconds before writing the disc.
-v verbose-level

cdrecord

cdrecord [general-options] dev=device [track-options] 
track1,track2...

Record data or audio compact discs. This program normally requires root access, and has a large number of options and settings. A number of useful examples can be found in the manpage, which is quite extensive.

General options

General option flags go directly after the cdrecord command. Options affecting the track arguments are placed after the device argument and before the track arguments themselves. The general options are:

--version

Print version information and exit.

-v

Verbose mode. Use one v for each level of verbosity: -vv would be very verbose, and -vvv would be even more so.

-V

As with the -v, a verbose mode counter. However, this applies only to SCSI transport messages. This will slow down the application.

--debug=n, -d

Set the debug level to an integer (greater numbers are more verbose), or use multiple -d flags as with the -v and -V flags.

--kdebug=n, --kd=n

Set the kernel's debug notification value to n during SCSI command execution. Works through the scg-driver.

-s, --silent

Silent mode. Do not print any SCSI error commands.

--force

Override errors if possible. May allow you to blank an otherwise broken CD-RW.

--dummy

Perform a dry run, doing all the steps of recording with the laser turned off. This will let you know whether the process is going to work.

--dao

Disk-at-once mode. Works only with MMC drives that support non-raw session-at-once modes.

--multi

Set to record in multisession mode. Must be present on all sessions but the last one for a multisession disc.

--msinfo

Get multisession information from the CD. Used only with multisession discs onto which you can still record more sessions.

--toc

Display the table of contents for the CD currently in the drive. Works for CD-ROM as well as CD-R and CD-RW drives.

--atip

Display the ATIP (Absolute Time In Pregroove) information for a disc. Only some drives allow you to read this information.

--fix

Close ("fixate") the session, preventing future multisession recordings and allowing the disc to be played in standard audio CD players (some can also play a disc that has not been closed).

--nofix

Do not close the disc after writing.

--load

Load media and exit. Works with tray-loading mechanisms only.

--eject

Eject disc after recording. Some hardware may need to eject a disc after a dummy recording and before the actual recording.

--speed=n

Set the speed to n, a multiple of the audio speed. Normally, cdrecord will get this from the CDR_SPEED environment variable. If your drive has trouble with higher numbers, try 0 as a value.

blank=type

Erase data from a CD-RW in one of the following ways:

help: Display a possible list of blanking methods.
all: Erase all information on the disc. May take a long time.
fast: Perform a quick erase of the disc, erasing only the PMA, TOC, and pregap.
track: Blank a track.
unreserve: Unreserve a track previously marked as reserved.
trtail: Blank the tail of a track only.
unclose: Unclose the last session.
session: Blank the last session.

fs=n

Set the fifo buffer size to n, in bytes. You may use k, m, s, or f to specify kilobytes, megabytes, or units of 2048 and 2352 bytes, respectively. The default is 4MB.

timeout=n

Set the timeout to n seconds. Defaults to 40.

driver=name

Lets you specify a driver for your system. Suggested for experts only. The special drivers cdr_simul and dvd_simul are used for simulation and profiling tests.

driveropts=optlist

Specify a comma-separated list of driver options. To get a list of valid options, use driveropts=help and --checkdrive.

--checkdrive

Check to see if there are valid drivers for the current drive. Returns 0 if the drive is valid.

--scanbus

Scan SCSI devices.

--reset

Attempt to reset the SCSI bus. Does not work on all systems.

--useinfo

Use .inf files to override audio options set elsewhere.

mcn=n

Set the Media Catalog Number to n.

The device argument

The device argument should be specified not as a file but as three integers representing the bus, target, and logical unit, as in the cdrdao command. To check the available options, use the --scanbus option.

Track options and arguments

Track options may be mixed with track arguments, and normally apply to the track immediately after them or to all tracks after them. The track arguments themselves should be the files that you will be writing to the CD. Options are:

isrc=n: Set the International Standard Recording Number for the track following this argument.
index=a,b,c: Set the index list for the next track. The values should be increasing comma-separated integers, starting with index 1 and counting in sectors (75ths of a second). For example, you could set three indices in a track with index=0,750,7500 and they would occur at the beginning of the track, after 10 seconds, and after 100 seconds.
--audio: Write all tracks after this track in digital audio format (playable by standard CD players). If you do not use this flag or the --data flag, cdrecord will assume that .au and .wav files are to be recorded as raw audio and that all other files are data.
--swab: Declare that your data is in byte-swapped (little-endian) byte order. This is not normally necessary.
--data: Record subsequent tracks as CD-ROM data. If you do not use this flag or the --audio flag, all files except for those ending in .wav or .au are assumed to be data.
--mode2: Write all subsequent tracks in CD-ROM mode 2 format.
--xa1, --xa2: Write subsequent tracks in CD-ROM XA mode 1 or CD-ROM XA mode 2 format.
--cdi: Write subsequent tracks in CDI format.
--isosize: The size of the next track should match the size of the ISO-9660 filesystem. This is used when duplicating CDs or copying from raw-data filesystems.
--pad: Insert 15 sectors of blank data padding between data tracks. Applies to all subsequent tracks or until you use the --nopad argument, and is overridden by the padsize=n argument.
padsize=n: Insert n sectors of blank data padding after the next track. Applies only to the track immediately after it.
--nopad: Do not insert blank data between data tracks following this flag. This is the default behavior.
tsize=n

cfdisk

cfdisk [options] [device]

System administration command. Partition a hard disk. Normally, device will be /dev/hda, /dev/hdb, /dev/sda, /dev/sdb, /dev/hdc, /dev/hdd, and so on. See also fdisk.

Options

-a: Highlight the current partition with a cursor, not reverse video.
-c cylinders: Specify the number of cylinders.
-g: Ignore driver-provided geometry; guess one instead.
-h heads: Specify the number of heads.
-s sectors: Specify the number of sectors per track.
-v: Print version number and exit.
-z: Do not read the partition table; partition from scratch.
-P format: Display the partition table in format, which must be r (raw data), s (sector order), or t (raw format).

Commands

up arrow, down arrow: Move among partitions.
b: Toggle partition's bootable flag.
d: Delete partition (allow other partitions to use its space).
g: Alter the disk's geometry. Prompt for what to change: cylinders, heads, or sectors (c, h, or s, respectively).
h: Help.
m: Attempt to ensure maximum usage of disk space in the partition.
n: Create a new partition. Prompt for more information.
p: Display the partition table.
q: Quit without saving information.
t: Prompt for a new filesystem type, and change to that type.
u: Change the partition size units, rotating from megabytes to sectors to cylinders and back.
W: Save information.

chage

chage [options] user

Change information about user password expirations. If run without any option flags, chage will prompt for values to be entered; you may also use option flags to change or view information.

Options

-l: This flag is used without any others, and causes chage to display the current password expiration attributes for the user.
-m mindays: Minimum number of days between password changes. Default is zero, meaning that the user may change the password at any time.
-M maxdays: Maximum number of days between password changes.
-d lastday: Date of last password change. This may be expressed as a date in YYYY-MM-DD format, or as the number of days between January 1, 1970 and the last password change.
-I inactive-days: If a password expires and the user does not log in for this number of days, the account will be locked, and the user must contact a system administrator before logging in. Set to 0 to disable the feature.
-E expiredate: Set the date when the account will be locked. This is not a date for password expiration, but for account expiration. It may be expressed as a YYYY-MM-DD date or as a number of days since January 1, 1970.
-W warning: The number of days before password expiration that a user will be warned to change passwords.

chat

chat [options] [script]

System administration command. Set up or initiate dial-up Internet connections; often used in conjunction with pppd, the PPP daemon. On some systems, chat takes the place of the dip program. A chat script is composed of a simple but expressive syntax of paired expect and send strings and sometimes substrings. A script string may contain either text expected from the modem or text to be sent, a chat directive, a substitution character, or a mixture of all three. When reading from a file, lines beginning with # are treated as comments.

Options

-e: Start script with the ECHO directive turned on.
-E: Allow script to read environment variables by using shell $VARIABLE syntax.
-f file: Read chat script from file instead of standard input.
-r file: Send the output of the REPORT directive to file. By default, they are sent to standard error.
-s: Send all error and log information to standard error, even when using the -v option.
-S: Silent mode; send neither error nor log messages to syslogd.
-t n: Set the default timeout value to n seconds. When not specified, the default timeout value is 45 seconds.
-T string: Set the string to be used instead of the \T substitution character. This is usually a phone number.
-U string: Set the string to be used instead of the \U substitution character. This is usually a second phone number.
-v: Verbose mode; log the chat script state and text sent to and received from the modem to syslogd.
-V: Standard error verbose mode; identical to -v, but send information to standard error instead of syslogd.

Chat directives

Scripts are built from paired strings, an expect string and a send string. A null string formed with two single quotes, '', tells chat to expect nothing and just send the send string. A hyphen, -, may be used in an expect string to specify an alternate expect and send in the event the first expect fails. chat will wait, expecting the first part of the string, and if it fails to receive it, it will perform the second part of the string, often a directive. For example:

ogin:-BREAK-ogin:

is interpreted by chat to mean expect the string "ogin:"; if it is not received before the timeout period, send a break signal to the modem, then expect "ogin:" again.

BREAK is an example of a chat directive, which is a special keyword that directs chat to take some action. Most directives are meant for use as expect strings. Some are meant to be special reply strings. BREAK can be used as a reply, or, as the above example shows, can be inserted into an expect substring. The following chat directives are recognized by chat:

ABORT string: If the modem returns the specified string, abort the script. This is often used to capture a modem status sent as a string, such as BUSY or NO CARRIER.
BREAK string: Reply string. Send a break signal to the modem. If the modem returns the specified string, abort the script. This is often used to capture a modem status sent as a string, such as BUSY or NO CARRIER.
CLR_ABORT string: Clear an ABORT string from memory.
CLR_ABORT string: Clear a REPORT string from memory.
ECHO status: Set ECHO to status ON or OFF. When on, chat will echo output from the modem to standard error.
EOT: Reply string. EOT is used as a send string. It instructs chat to send an end-of-file character. This can also be embedded in a string using the character sequence ^D.
REPORT string: When the script receives string, write it and any characters following it to standard error.
HANGUP status: Set HANGUP to status ON or OFF. When on, chat will treat a modem hanging up as an error. When off, it will continue to process the script. You usually want to set this to on after the modem has connected.
SAY string: Print the string to the standard error. This can be used to communicate with the script's user.
TIMEOUT n: Set the timeout value for subsequent expect strings to n seconds.

Substitution characters

'': The null string. When used in place of a send string, chat sends a return character. When used in an expect string, chat expects nothing and just sends the send string.
\b: Backspace character.
\c: Used at the end of a string. Suppresses the newline character automatically added to send strings. Not valid in expect strings.
\d: Pause one second. Not valid in expect strings.
\n: The newline character.
\N, \0: The null character.
\p: Pause one tenth of a second. Not valid in expect strings.
\xd5: Mask this string. Write the string ?????? instead when writing to the system log. Not valid in expect strings.
\r: The carriage return character.
\t: The tab character.
\T: The string specified with the -T option, usually a phone number. Not valid in expect strings.
\U: The string specified with the -U option, usually a second phone number. Not valid in expect strings.
\\: The backslash character.
\ddd: An ASCII character expressed in octal. Not valid in expect strings.
^char: Substitute a control character for char.
@file: Substitute the contents of file. Not valid in expect strings.
$NAME: When using the -E option, substitute the value of the specified environment variable NAME, or substitute nothing if the variable is not set.

Exit codes

0: Script terminated normally.
1: Invalid parameter or expect string. Script failed.
2: Error during execution. Script failed.
3: Expect string timeout with no further instructions. Script halted.
4 and up

chattr

chattr [options] mode files

Modify file attributes. Specific to Linux Second and Third Extended Filesystem (ext2 and ext3). Behaves similarly to symbolic chmod, using +, -, and =. mode is in the form opcode attribute. See also lsattr.

Options

-R: Modify directories and their contents recursively.
-V: Print modes of attributes after changing them.
-v version: Set the file's version.

Opcodes

+: Add attribute.
-: Remove attribute.
=: Assign attributes (removing unspecified attributes).

Attributes

A: Don't update access time on modify.
a: Append only for writing. Can be set or cleared only by a privileged user.
c: Compressed.
d: No dump.
i: Immutable. Can be set or cleared only by a privileged user.
j: Journalled file. This is useful only in cases where you are using an ext3 filesystem mounted with the data="ordered" or data="writeback" attributes. The data="journalled" option for the filesystem causes this operation to be performed for all files in the system and makes this option irrelevant.
S: Synchronous updates.
s: Secure deletion. The contents are zeroed on deletion, and the file cannot be undeleted or recovered in any way.
u: Undeletable. This causes a file to be saved even after it has been deleted, so that a user can undelete it later.

Example

chattr +a myfile     As superuser

checkpc

checkpc [options]

System administration command. Examine and optionally repair the LPRng printer capability database and related files. Entries in this database control the printing and spooling of print jobs. The checkpc command reports incorrect entries in /etc/printcap and ensures that files and directories used by LPRng exist and have the correct permissions.

Options

-a: Don't create missing accounting files specified in :af entries.
-c: Print verbose configuration details.
-D: Run with debugging flags on.
-f: Fix database by creating missing files and changing incorrect file permissions.
-h: Print help message and exit.
-l: Don't create missing logging files specified in :lf entries.
-p: Print information about printcap database.
-r: Remove old job files. Use -A to set the maximum age for job files.
-s: Don't create missing filter status files specified in :ps entries.
-t size[unit]: Truncate log files to specified size. You may specify the unit of that size in k or M for kilobytes or megabytes. The default is megabytes.
-A age[unit]: Report junk or job files older than age. A unit of D, H, M, or S may be used to specify that age represents days, hours, minutes, or seconds. The default is days.
-P printer: Check or fix entries only for the specified printer.
-V: Verbose mode. Report on progress of checkpc including all entries checked and repairs made.

chfn

chfn [options] [username]

Change the information that is stored in /etc/passwd and displayed to the finger query. Without options, chfn enters interactive mode and prompts for changes. To make a field blank, enter the keyword none. Only a privileged user can change information for another user. For regular users, chfn prompts for the user's password before making the change.

Options

-f, --full-name: Specify new full name.
-h, --home-phone: Specify new home phone number.
-o, --office: Specify new office number.
-p, --office-phone: Specify new office phone number.
-u, --usage, --help: Print help message and then exit.
-v, --version: Print version information and then exit.

Example

chfn -f "Ellen Siever" ellen

chgrp

chgrp [options] newgroup files
chgrp [options]

Change the group of one or more files to newgroup. newgroup is either a group ID number or a group name located in /etc/group. Only the owner of a file or a privileged user may change the group.

Options

-c, --changes: Print information about files that are changed.
-f, --silent, --quiet: Do not print error messages about files that cannot be changed.
--help: Print help message and then exit.
-R, --recursive: Traverse subdirectories recursively, applying changes.
--reference=filename: Change the group to that associated with filename. In this case, newgroup is not specified.
-v, --verbose: Verbosely describe ownership changes.
--version: Print version information and then exit.

chmod

chmod [options] mode files
chmod [options] --reference=filename files

Change the access mode (permissions) of one or more files. Only the owner of a file or a privileged user may change the mode. mode can be numeric or an expression in the form of who opcode permission. who is optional (if omitted, default is a); choose only one opcode. Multiple modes are separated by commas.

Options

-c, --changes: Print information about files that are changed.
-f, --silent, --quiet: Do not notify user of files that chmod cannot change.
--help: Print help message and then exit.
-R, --recursive: Traverse subdirectories recursively, applying changes.
--reference=filename: Change permissions to match those associated with filename.
-v, --verbose: Print information about each file, whether changed or not.
--version: Print version information and then exit.

Who

u: User.
g: Group.
o: Other.
a: All (default).

Opcode

+: Add permission.
-: Remove permission.
=: Assign permission (and remove permission of the unspecified fields).

Permissions

r: Read.
w: Write.
x: Execute.
s: Set user (or group) ID.
t: Sticky bit; used on directories to prevent removal of files by non-owners.
u: User's present permission.
g: Group's present permission.
o: Other's present permission.

Alternatively, specify permissions by a three-digit octal number. The first digit designates owner permission; the second, group permission; and the third, other's permission. Permissions are calculated by adding the following octal values:

4: Read.
2: Write.
1: Execute.

Note that a fourth digit may precede this sequence. This digit assigns the following modes:

4: Set user ID on execution to grant permissions to process based on the file's owner, not on permissions of the user who created the process.
2: Set group ID on execution to grant permissions to process based on the file's group, not on permissions of the user who created the process.
1: Set sticky bit.

Examples

Add execute-by-user permission to file:

chmod u+x file

Either of the following will assign read/write/execute permission by owner (7), read/execute permission by group (5), and execute-only permission by others (1) to file:

chmod 751 file
chmod u=rwx,g=rx,o=x file

Any one of the following will assign read-only permission to file for everyone:

chmod =r file
chmod 444 file
chmod a-wx,a+r file

The following makes the executable setuid, assigns read/write/execute permission by owner, and assigns read/execute permission by group and others:

chmod 4755 file

chown

chown [options] newowner files
chown [options] --reference=filename files

Change the ownership of one or more files to newowner. newowner is either a user ID number or a login name located in /etc/passwd. chown also accepts users in the form newowner:newgroup or newowner.newgroup. The last two forms change the group ownership as well. If no owner is specified, the owner is unchanged. With a period or colon but no group, the group is changed to that of the new owner. Only the current owner of a file or a privileged user may change the owner.

Options

-c, --changes: Print information about files that are changed.
--dereference: Follow symbolic links.
-f, --silent, --quiet: Do not print error messages about files that cannot be changed.
-h, --no-dereference: Change the ownership of each symbolic link (on systems that allow it) rather than the referenced file.
-v, --verbose: Print information about all files that chown attempts to change, whether or not they are actually changed.
-R, --recursive: Traverse subdirectories recursively, applying changes.
--reference=filename: Change owner to the owner of filename instead of specifying a new owner explicitly.
--help: Print help message and then exit.
--version: Print version information and then exit.

chpasswd

chpasswd [option]

System administration command. Change user passwords in a batch. chpasswd accepts input in the form of one username:password pair per line. If the -e option is not specified, password is encrypted before being stored.

Option

-e: Passwords given are already encrypted.

chroot

chroot newroot [command]

System administration command. Change root directory for command or, if none is specified, for a new copy of the user's shell. This command or shell is executed relative to the new root. The meaning of any initial / in pathnames is changed to newroot for a command and any of its children. In addition, the initial working directory is newroot. This command is restricted to privileged users.

chsh

chsh [options] [username]

Change your login shell, either interactively or on the command line. Warn if shell does not exist in /etc/shells. Specify the full path to the shell. chsh prompts for your password. Only a privileged user can change another user's shell.

Options

-l, --list-shells: Print valid shells, as listed in /etc/shells, and then exit.
-s shell, --shell shell: Specify new login shell.
-u, --help: Print help message and then exit.
-v, --version: Print version information and then exit.

Example

chsh -s /bin/tcsh

chvt

chvt N

Switch to virtual terminal N (that is, switch to /dev/ttyN). If you have not created /dev/ttyN, it will be created when you use this command. There are keyboard shortcuts for this functionality as well. From a graphical desktop, you can press Ctrl-Alt-F1 through F12 to switch to different virtual terminals. In text mode, you can skip the Ctrl key and just use Alt-F1 through F12. To switch back to graphical mode, use Alt-F7.

cksum

cksum [files]

Compute a cyclic redundancy check (CRC) checksum for all files; this is used to ensure that a file was not corrupted during transfer. Read from standard input if the character - or no files are given. Display the resulting checksum, the number of bytes in the file, and (unless reading from standard input) the filename.

clear

clear

Clear the terminal display.

cmp

cmp [options] file1 file2 [skip1 [skip2]]

Compare file1 with file2. Use standard input if file1 is - or missing. This command is normally used for comparing binary files, although files can be of any type. (See also comm and diff.) skip1 and skip2 are optional offsets in the files at which the comparison is to start.

Options

-c, --print-chars: Print differing bytes as characters.
-i num, --ignore-initial=num: Ignore the first num bytes of input.
-l, --verbose: Print offsets and codes of all differing bytes.
-s, --quiet, --silent: Work silently; print nothing, but return exit codes:
0: Files are identical.
1: Files are different.
2: Files are inaccessible.

Example

Print a message if two files are the same (exit code is 0):

cmp -s old new && echo 'no changes'

col

col [options]

A postprocessing filter that handles reverse linefeeds and escape characters, allowing output from tbl or nroff to appear in reasonable form on a terminal.

Options

-b: Ignore backspace characters; helpful when printing manpages.
-f: Process half-line vertical motions, but not reverse line motion. (Normally, half-line input motion is displayed on the next full line.)
-l n: Buffer at least n lines in memory. The default buffer size is 128 lines.
-x: Normally, col saves printing time by converting sequences of spaces to tabs. Use -x to suppress this conversion.

Examples

Run myfile through tbl and nroff, then capture output on screen by filtering through col and more:

tbl myfile | nroff | col | more

Save manpage output for the ls command in out.print, stripping out backspaces (which would otherwise appear as ^H):

man ls | col -b > out.print

colcrt

colcrt [options] [files]

A postprocessing filter that handles reverse linefeeds and escape characters, allowing output from tbl or nroff to appear in reasonable form on a terminal. Put half-line characters (e.g., subscripts or superscripts) and underlining (changed to dashes) on a new line between output lines.

Options

-: Do not underline.
-2: Double space by printing all half-lines.

colrm

colrm [start [stop]]

Remove specified columns from a file, where a column is a single character in a line. Read from standard input and write to standard output. Columns are numbered starting with 1; begin deleting columns at (including) the start column, and stop at (including) the stop column. Entering a tab increments the column count to the next multiple of either the start or stop column; entering a backspace decrements it by 1.

Example

colrm 3 5 < test1 > test2

column

column [options] [files]

Format input from one or more files into columns, filling rows first. Read from standard input if no files are specified.

Options

-c num: Format output into num columns.
-s char: Delimit table columns with char. Meaningful only with -t.
-t: Format input into a table. Delimit with whitespace, unless an alternate delimiter has been provided with -s.
-x: Fill columns before filling rows.

comm

comm [options] file1 file2

Compare lines common to the sorted files file1 and file2. Three-column output is produced: lines unique to file1, lines unique to file2, and lines common to both files. comm is similar to diff in that both commands compare two files. But comm can also be used like uniq; comm selects duplicate or unique lines between two sorted files, whereas uniq selects duplicate or unique lines within the same sorted file.

Options

-: Read the standard input.
-num: Suppress printing of column num. Multiple columns may be specified and should not be space-separated.
--help: Print help message and exit.
--version: Print version information and exit.

Example

Compare two lists of top-10 movies, and display items that appear in both lists:

comm -12 siskel_top10 ebert_top10

compress

compress [options] files

Compress one or more files, replacing each with the compressed file of the same name with .Z appended. If no file is specified, compress standard input. Each file specified is compressed separately. compress ignores files that are symbolic links. See also gzip and bzip2, which are more commonly used now.

Options

-b maxbits: Limit the maximum number of bits.
-c: Write output to standard output, not to a .Z file.
-d: Decompress instead of compressing. Same as uncompress.
-f: Force generation of an output file even if one already exists.
-r: If any of the specified files is a directory, compress recursively.
-v: Print compression statistics.
-V: Print version and compilation information and then exit.

cp [options] file1 file2
cp [options] files directory

Copy file1 to file2, or copy one or more files to the same names under directory. If the destination is an existing file, the file is overwritten; if the destination is an existing directory, the file is copied into the directory (the directory is not overwritten).

Options

-a, --archive

Preserve attributes of original files where possible. The same as -dpR.

-b, --backup

Back up files that would otherwise be overwritten.

-d, --no-dereference

Do not dereference symbolic links; preserve hard link relationships between source and copy.

-f, --force

Remove existing files in the destination.

-i, --interactive

Prompt before overwriting destination files.

-l, --link

Make hard links, not copies, of nondirectories.

-p, --preserve

Preserve all information, including owner, group, permissions, and timestamps.

-P, --parents

Preserve intermediate directories in source. The last argument must be the name of an existing directory. For example, the command:

cp --parents jphekman/book/ch1 newdir

copies the file jphekman/book/ch1 to the file newdir/jphekman/book/ch1, creating intermediate directories as necessary.

-r, -R, --recursive

Copy directories recursively.

-S backup-suffix, --suffix=backup-suffix

Set suffix to be appended to backup files. This may also be set with the SIMPLE_BACKUP_SUFFIX environment variable. The default is ~. You need to explicitly include a period if you want one before the suffix (for example, specify .bak, not bak).

-s, --symbolic-link

Make symbolic links instead of copying. Source filenames must be absolute.

-u, --update

Do not copy a file to an existing destination with the same or newer modification time.

-v, --verbose

Before copying, print the name of each file.

-V type, --version-control=type

Set the type of backups made. You may also use the VERSION_CONTROL environment variable. The default is existing. Valid arguments are:

t, numbered: Always make numbered backups.
nil, existing: Make numbered backups of files that already have them; otherwise, make simple backups.
never, simple: Always make simple backups.

-x, --one-file-system

Ignore subdirectories on other filesystems.

Example

Copy the contents of the guest directory recursively into the archives/guest/ directory, and display a message for each file copied:

cd /archives && cp -av /home/guest guest

cpio

cpio flags [options]

Copy file archives from or to tape or disk, or to another location on the local machine. Each of the three flags -i, -o, or -p accepts different options.

Flags

-i, --extract [options] [patterns]: Copy in (extract) from an archive files whose names match selected patterns. Each pattern can include Bourne shell filename metacharacters. (Patterns should be quoted or escaped so that they are interpreted by cpio, not by the shell.) If pattern is omitted, all files are copied in. Existing files are not overwritten by older versions from the archive unless -u is specified.
-o, --create [options]: Copy out to an archive a list of files whose names are given on the standard input.
-p, --pass-through [options] directory: Copy (pass) files to another directory on the same system. Destination pathnames are interpreted relative to the named directory.

Comparison of valid options

Options available to the -i, -o, and -p flags are shown here (the - is omitted for clarity):

i:   bcdf mnrtsuv B SVCEHMR IF
o: 0a c         vABL VC HM O F
p: 0a  d lm    uv  L V    R

Options

-0, --null

Expect list of filenames to be terminated with null, not newline. This allows files with a newline in their names to be included.

-a, --reset-access-time

Reset access times of input files after reading them.

-A, --append

Append files to an existing archive, which must be a disk file. Specify this archive with -O or -F.

-b, --swap

Swap bytes and half-words to convert between big-endian and little-endian 32-bit integers.

-B

Block input or output using 5120 bytes per record (default is 512 bytes per record).

--blocksize=size

Set input or output blocksize to size × 512 bytes.

-c

Read or write header information as ASCII characters; useful when source and destination machines are different types.

-C n, --io-size=n

Like -B, but blocksize can be any positive integer n.

-d, --make-directories

Create directories as needed.

-E file, --pattern-file=file

Extract from the archives filenames that match patterns in file.

-f, --nonmatching

Reverse the sense of copying; copy all files except those that match patterns.

-F file, --file=file

Use file as the archive, not stdin or stdout. file can reside on another machine, if given in the form user@hostname:file (where user@ is optional).

--force-local

Assume that file (provided by -F, -I, or -O) is a local file, even if it contains a colon (:) indicating a remote file.

-H type, --format=type

Use type format. Default for copy-out is bin; default for copy-in is autodetection of the format. Valid formats (all caps also accepted) are:

bin: Binary.
odc: Old (POSIX.1) portable format.
newc: New (SVR4) portable format.
crc: New (SVR4) portable format with checksum added.
tar: Tar.
ustar: POSIX.1 tar (also recognizes GNU tar archives).
hpbin: HP-UX's binary (obsolete).
hpodc: HP-UX's portable format.

-I file

Read file as an input archive. May be on a remote machine (see -F).

-k

Ignored. For backward compatibility.

-l, --link

Link files instead of copying.

-L, --dereference

Follow symbolic links.

-m, --preserve-modification-time

Retain previous file modification time.

-M msg, --message=msg

Print msg when switching media, as a prompt before switching to new media. Use variable %d in the message as a numeric ID for the next medium. -M is valid only with -I or -O.

-n, --numeric-uid-gid

When verbosely listing contents, show user ID and group ID numerically.

--no-absolute-filenames

Create all copied-in files relative to the current directory.

--no-preserve-owner

Make all copied files owned by yourself, instead of the owner of the original. Can be used only if you are a privileged user.

-O file

Archive the output to file, which may be a file on another machine (see -F).

--only-verify-crc

For a CRC-format archive, verify the CRC of each file; don't actually copy the files in.

--quiet

Don't print the number of blocks copied.

-r

Rename files interactively.

-R [user][:group], --owner [user][:group]

Reassign file ownership and group information to the user's login ID (privileged users only).

-s, --swap-bytes

Swap bytes of each two-byte half-word.

-S, --swap-half-words

Swap half-words of each four-byte word.

--sparse

For copy-out and copy-pass, write files that have large blocks of zeros as sparse files.

-t, --list

Print a table of contents of the input (create no files). When used with the -v option, resembles output of ls -l.

-u, --unconditional

Unconditional copy; old files can overwrite new ones.

-v, --verbose

Print a list of filenames processed.

-V, --dot

Print a dot for each file read or written (this shows cpio at work without cluttering the screen).

--version

Print version number and then exit.

Examples

Generate a list of files whose names end in .old using find; use the list as input to cpio:

find . -name "*.old" -print | cpio -ocBv > /dev/rst8

Restore from a tape drive all files whose names contain save (subdirectories are created if needed):

cpio -icdv "*save*" < /dev/rst8

Move a directory tree:

find . -depth -print | cpio -padm /mydir

cpp

cpp [options] [ ifile [ ofile ] ]

GNU C language preprocessor. cpp is normally invoked as the first pass of any C compilation by the gcc command. The output of cpp is a form acceptable as input to the next pass of the C compiler. The ifile and ofile options are, respectively, the input and output for the preprocessor; they default to standard input and standard output.

Options

-$

Do not allow $ in identifiers.

-ansi

Use 1990 ISO C standard. This is equivalent to -std=c89.

-dD

-dM

Suppress normal output. Print series of #defines that create the macros used in the source file.

-dN

-dI

Print #include directives in addition to other output.

-fpreprocessed

Treat file as already preprocessed. Skip most processing directives, remove all comments, and tokenize file.

-ftabstop=width

Set distance between tabstops so columns will be reported correctly in warnings and errors. Default is 8.

-fno-show-column

Omit column numbers in warnings and errors.

-gcc

Define _ _GNUC_ _, _ _GNUC_MINOR_ _, and _ _GNUC_PATCHLEVEL_ _ macros.

--help

Print usage message and exit.

-idirafter dir

Search dir for header files when a header file is not found in any of the included directories.

-imacros file

Process macros in file before processing main files.

-include file

Process file before main file.

-iprefix prefix

When adding directories with -iwithprefix, prepend prefix to the directory's name.

-isystem dir

Search dir for header files after searching directories specified with -I but before searching standard system directories.

-iwithprefix dir

Append dir to the list of directories to be searched when a header file cannot be found in the main include path. If -iprefix has been set, prepend that prefix to the directory's name.

-iwithprefixbefore dir

Insert dir at the beginning of the list of directories to be searched when a header file cannot be found in the main include path. If -iprefix has been set, prepend that prefix to the directory's name.

-lang-c, -lang-c++, -lang-objc, -lang-objc++

Expect the source to be in C, C++, Objective C, or Objective C++, respectively.

-lint

Display all lint commands in comments as #pragma lint command.

-nostdinc

Search only specified, not standard, directories for header files.

-nostdinc++

Suppress searching of directories believed to contain C++-specific header files.

-o file

Write output to file. (Same as specifying a second filename in the command line.)

-pedantic

Warn verbosely.

-pedantic-errors

Produce a fatal error in every case in which -pedantic would have produced a warning.

-std=standard

Specify C standard of input file. Accepted values are:

iso9899:1990, c89: 1990 ISO C standard.
iso9899:199409: 1994 amendment to the 1990 ISO C standard.
iso9899:1999, c99, iso9899:199x, c9x: 1999 revised ISO C standard.
gnu89: 1990 C Standard with gnu extensions. The default value.
gnu99, gnu9x: 1999 revised ISO C standard with gnu extensions.

-traditional

Behave like traditional C, not ANSI.

-trigraphs

Convert special three-letter sequences, meant to represent missing characters on some terminals, into the single character they represent.

-undef

Suppress definition of all nonstandard macros.

-v

Print version number, then process file.

-version

--version

Print version number then exit.

-w

Don't print warnings.

-x language

Specify the language of the input file. language may be c, c++, objective-c, or assembler-with-cpp. By default, language is deduced from the filename extension. If the extension is unrecognized, the default is c.

-A name[=def]

Assert name with value def as if defined by #assert. To turn off standard assertions, use -A-.

-A -name[=def]

Cancel assertion name with value def.

-C

Retain all comments except those found on cpp directive lines. By default, cpp strips C-style comments.

-Dname[=def]

Define name with value def as if by a #define. If no =def is given, name is defined with value 1. -D has lower precedence than -U.

-E

Preprocess the source files, but do not compile. Print result to standard output. This option is usually passed from gcc.

-H

Print pathnames of included files, one per line, on standard error.

-Idir

Search in directory dir for #include files whose names do not begin with / before looking in directories on standard list. #include files whose names are enclosed in double quotes and do not begin with / will be searched for first in the current directory, then in directories named on -I options, and last in directories on the standard list.

-I-

Split includes. Search directories specified by -I options preceding this one for header files included with quotes (#include "file.h") but not for header files included with angle brackets (#include <file.h>). Search directories specified by -I options following this one for all header files.

-M [-MG]

Suppress normal output. Print a rule for make that describes the main source file's dependencies. If -MG is specified, assume that missing header files are actually generated files, and look for them in the source file's directory.

-MF file

Print rules generated by -M or -MM to file.

-MD file

-MM

-MMD file

-MQ target

-MT target

Specify the target to use when generating a rule for make. By default the target is based on the name of the main input file.

-P

Preprocess input without producing line-control information used by next pass of the C compiler.

-Uname

Remove any initial definition of name, where name is a reserved symbol predefined by the preprocessor or a name defined on a -D option. Names predefined by cpp are unix and i386 (for Intel systems).

-Wall

Warn both on nested comments and trigraphs.

-Wcomment, -Wcomments

Warn when encountering the beginning of a nested comment.

-Wtraditional

Warn when encountering constructs that are interpreted differently in ANSI than in traditional C.

-Wtrigraph, -Wcomments

Warn when encountering trigraphs, three-letter sequences meant to represent missing characters on some terminals.

Special names

cpp understands various special names, some of which are:

_ _DATE_ _: Current date (e.g., Jan 10 2003).
_ _FILE_ _: Current filename (as a C string).
_ _LINE_ _: Current source line number (as a decimal integer).
_ _TIME_ _: Current time (e.g., 12:00:00).

These special names can be used anywhere, including in macros, just like any other defined names. cpp's understanding of the line number and filename may be changed using a #line directive.

Directives

All cpp directive lines start with # in column 1. Any number of blanks and tabs is allowed between the # and the directive. The directives are:

#assert name (string): Define a question called name, with an answer of string. Assertions can be tested with #if directives. The predefined assertions for #system, #cpu, and #machine can be used for architecture-dependent changes.
#unassert name: Remove assertion for question name.
#define name token-string: Define a macro called name, with a value of token-string. Subsequent instances of name are replaced with token-string.
#define name( arg, ... , arg ) token-string: This allows substitution of a macro with arguments. token-string will be substituted for name in the input file. Each call to name in the source file includes arguments that are plugged into the corresponding args in token-string.
#undef name: Remove definition of the macro name. No additional tokens are permitted on the directive line after name.
#ident string: Put string into the comment section of an object file.
#include "filename", #include<filename>: Include contents of filename at this point in the program. No additional tokens are permitted on the directive line after the final " or >.
#line integer-constant "filename": Cause cpp to generate line-control information for the next pass of the C compiler. The compiler behaves as if integer-constant is the line number of the next line of source code and filename (if present) is the name of the input file. No additional tokens are permitted on the directive line after the optional filename.
#endif: End a section of lines begun by a test directive (#if, #ifdef, or #ifndef). No additional tokens are permitted on the directive line.
#ifdef name: Lines following this directive and up to matching #endif or next #else or #elif will appear in the output if name is currently defined. No additional tokens are permitted on the directive line after name.
#ifndef name: Lines following this directive and up to matching #endif or next #else or #elif will appear in the output if name is not currently defined. No additional tokens are permitted on the directive line after name.
#if constant-expression: Lines following this directive and up to matching #endif or next #else or #elif will appear in the output if constant-expression evaluates to nonzero.
#elif constant-expression: An arbitrary number of #elif directives are allowed between an #if, #ifdef, or #ifndef directive and an #else or #endif directive. The lines following the #elif and up to the next #else, #elif, or #endif directive will appear in the output if the preceding test directive and all intervening #elif directives evaluate to zero, and the constant-expression evaluates to nonzero. If constant-expression evaluates to nonzero, all succeeding #elif and #else directives will be ignored.
#else: Lines following this directive and up to the matching #endif will appear in the output if the preceding test directive evaluates to zero, and all intervening #elif directives evaluate to zero. No additional tokens are permitted on the directive line.
#error: Report fatal errors.
#warning

cron

cron

System administration command. Normally started in a system startup file. Execute commands at scheduled times, as specified in users' files in /var/spool/cron. Each file shares its name with the user who owns it. The files are controlled via the command crontab. The cron command will also read commands from the /etc/crontab file and from the /etc/cron.d/ directory.

crontab

crontab [options] [file]

View, install, or uninstall your current crontab file. A privileged user can run crontab for another user by supplying -u user. A crontab file is a list of commands, one per line, that will execute automatically at a given time. Numbers are supplied before each command to specify the execution time. The numbers appear in five fields, as follows:

Minute              0-59
Hour             0-23
Day of month      1-31
Month            1-12
                 Jan, Feb, Mar, ...
Day of week              0-6, with 0 = Sunday
                 Sun, Mon, Tue, ...

Use a comma between multiple values, a hyphen to indicate a range, and an asterisk to indicate all possible values. For example, assuming these crontab entries:

59 3 * * 5     find / -print | backup_program
0 0 1,15 * *   echo "Timesheets due" | mail user

the first command backs up the system files every Friday at 3:59 a.m., and the second command mails a reminder on the 1st and 15th of each month.

The superuser can always issue the crontab command. Other users must be listed in the file /etc/cron.allow if it exists; otherwise, they must not be listed in /etc/cron.deny. If neither file exists, only the superuser can issue the command.

Options

The -e, -l, and -r options are not valid if any files are specified.

-e: Edit the user's current crontab file (or create one).
-l: Display the user's crontab file on standard output.
-r: Delete the user's crontab file.
-u user: Indicate which user's crontab file will be acted upon.

csh

csh [options] [file [arguments]]

C shell, a command interpreter into which all other commands are entered. On Linux, csh has been replaced with an enhanced version of the shell called tcsh. For more information, see Chapter 8.

csplit

csplit [options] file arguments

Separate file into context-based sections and place sections in files named xx00 through xxn (n < 100), breaking file at each pattern specified in arguments. See also split.

Options

-

Read from standard input.

-b suffix, --suffix-format=suffix

Append suffix to output filename. This option causes -n to be ignored. suffix must specify how to convert the binary integer to readable form by including one of the following: %d, %i, %u, %o, %x, or %X. The value of suffix determines the format for numbers as follows:

%d: Signed decimal.
%i: Same as %d.
%u: Unsigned decimal.
%o: Octal.
%x: Hexadecimal.
%X: Same as %x.

-f prefix, --prefix=prefix

Name new files prefix00 through prefixn (default is xx00 through xxn).

-k, --keep-files

Keep newly created files even when an error occurs (which would normally remove these files). This is useful when you need to specify an arbitrarily large repeat argument, {n}, and you don't want an out-of-range error to cause removal of the new files.

-n num, --digits=num

Use output filenames with numbers num digits long. The default is 2.

-s, -q, --silent, --quiet

Suppress all character counts.

-z, --elide-empty-files

Do not create empty output files. However, number as if those files had been created.

Arguments

Any one or a combination of the following expressions may be specified as arguments. Arguments containing blanks or other special characters should be surrounded by single quotes.

/expr/[offset]: Create file from the current line up to the line containing the regular expression expr. offset should be of the form +n or -n, where n is the number of lines below or above expr.
%expr%[offset]: Same as /expr/, except no file is created for lines previous to line containing expr.
num: Create file from current line up to (but not including) line number num. When followed by a repeat count (number inside { }), put the next num lines of input into another output file.
{n}: Repeat argument n times. May follow any of the preceding arguments. Files will split at instances of expr or in blocks of num lines. If * is given instead of n, repeat argument until input is exhausted.

Examples

Create up to 20 chapter files from the file novel:

csplit -k -f chap. novel '/CHAPTER/' '{20}'

Create up to 100 address files (xx00 through xx99), each four lines long, from a database named address_list:

csplit -k address_list 4 {99}

ctags

ctags [options] files

Create a list of function and macro names defined in a programming source file. More than one file may be specified. ctags understands many programming languages, including C, C++, FORTRAN, Java, Perl, Python, flex, yacc, and bison. The output list (named tags by default) contains lines of the form:

name     file     context

where name is the function or macro name, file is the source file in which name is defined, and context is a search pattern that shows the line of code containing name. After the list of tags is created, you can invoke vi on any file and type:

:set tags=tagsfile
:tag name

This switches the vi editor to the source file associated with the name listed in tagsfile (which you specify with -t).

etags produces an equivalent file for tags to be used with Emacs.

Options

-a: Append tag output to existing list of tags.
-e: Create tag files for use with emacs.
-h extensionlist: Interpret files with filename extensions specified in extensionlist as header files. The default list is ".h.H.hh.hpp.hxx.h++.inc.def". To indicate that files without extensions should be treated as header files, insert an additional period in the list before another period or at the end of the list, or use just a period by itself. To use this option multiple times and have the specified lists ANDed together, use a plus sign as the first character in the list. To restore the default, use the word "default".
-n: Use numeric ex commands to locate tags. Same as --excmd= number.
-o file, -f file, --output=file: Write to file.
--packages-only: Include tag entries for members of structure-like constructs.
-R: Recursively read files in subdirectories of the directory given on the command line.
-u: Don't sort tag entries.
-x: Produce a tabular listing of each function, and its line number, source file, and context.
-B: Search for tags backward through files.
-I tokenlist: Specify a list of tokens to be specially handled. If given as a file, use ex pattern commands to locate tags. Same as --excmd= pattern.
-N: Use ex pattern commands to locate tags. Same as --excmd= pattern.
-S, --ignore-indentation: Normally ctags uses indentation to parse the tag file; this option tells ctags to rely on indentation less.
-T, --typedefs-and-c++: Include tag entries for typedefs, structs, enums, unions, and C++ member functions.
-V, --version: Print the version number and exit.

cut

cut options [files]

Cut out selected columns or fields from one or more files. In the following options, list is a sequence of integers. Use a comma between separate values, and a hyphen to specify a range (e.g., 1-10,15,20 or 50-). See also paste and join.

Options

-b list, --bytes list: Specify list of positions; only bytes in these positions will be printed.
-c list, --characters list: Cut the column positions identified in list.
-d c, --delimiter c: Use with -f to specify field delimiter as character c (default is tab); special characters (e.g., a space) must be quoted.
-f list, --fields list: Cut the fields identified in list.
-n: Don't split multibyte characters.
-s, --only-delimited: Use with -f to suppress lines without delimiters.
--output-delimiter=string: Use string as the output delimiter. By default, the output delimiter is the same as the input delimiter.
--help: Print help message and exit.
--version: Print version information and exit.

Examples

Extract usernames and real names from /etc/passwd:

cut -d: -f1,5 /etc/passwd

Find out who is logged on, but list only login names:

who | cut -d" " -f1

Cut characters in the fourth column of file, and paste them back as the first column in the same file:

cut -c4 file | paste - file

cvs

cvs [options] cvs-command [command-options] [command-args]

CVS (Concurrent Versions System) is a version control system. Like earlier version control systems such as RCS, CVS tracks versions, permits the storage and retrieval of earlier versions, and allows tracking of the history of a file or an entire project. In addition, it permits multiple users on different systems across a network to work in a file simultaneously and merge their changes. All CVS commands start with cvs, followed by any global options, the command to execute, and any command options or arguments. For more information on CVS and its commands, see Chapter 15.

date

date [options] [+format] [date]

Print the current date and time. You may specify a display format. format can consist of literal text strings (blanks must be quoted) as well as field descriptors, whose values will appear as described in the following entries (the listing shows some logical groupings). A privileged user can change the system's date and time.

Options

+format

Display current date in a nonstandard format. For example:

$ date +"%A %j %n%k %p"
Tuesday 248
15 PM

The default is %a %b %e %T %Z %Y (e.g., Tue Sep 5 14:59:37 EDT 2000).

-d date, --date date

Display date, which should be in quotes and may be in the format d days or m months d days to print a date in the future. Specify ago to print a date in the past. You may include formatting (see the following section).

-f datefile, --file=datefile

Like -d, but printed once for each line of datefile.

-I [timespec], --iso-8601[=timespec]

Display in ISO-8601 format. If specified, timespec can have one of the values date (for date only), hours, minutes, or seconds to get the indicated precision.

-r file, --reference=file

Display the time file was last modified.

-R, --rfc-822

Display the date in RFC 822 format.

--help

Print help message and exit.

--version

Print version information and exit.

-s date, --set date

Set the date.

-u, --universal

Set the date to Greenwich Mean Time, not local time.

Format

The exact result of many of these codes is locale-specific and depend upon your language setting, particularly the LANG environment variable. See locale.

%: Literal %.
- (hyphen): Do not pad fields (default: pad fields with zeros).
_ (underscore): Pad fields with space (default: zeros).
%a: Abbreviated weekday.
%b: Abbreviated month name.
%c: Country-specific date and time format.
%d: Day of month (01-31).
%h: Same as %b.
%j: Julian day of year (001-366).
%k: Hour in 24-hour format, without leading zeros (0-23).
%l: Hour in 12-hour format, without leading zeros (1-12).
%m: Month of year (01-12).
%n: Insert a new line.
%p: String to indicate AM or PM.
%r: Time in %I:%M:%S %p (12-hour) format.
%s: Seconds since "the epoch," which is 1970-01-01 00:00:00 UTC (a nonstandard extension).
%t: Insert a tab.
%w: Day of week (Sunday = 0).
%x: Country-specific date format based on locale.
%y: Last two digits of year (00-99).
%z: RFC 822-style numeric time zone.
%A: Full weekday.
%B: Full month name.
%D: Date in %m/%d/%y format.
%H: Hour in 24-hour format (00-23).
%I: Hour in 12-hour format (01-12).
%M: Minutes (00-59).
%S: Seconds (00-59).
%T: Time in %H:%M:%S format.
%U: Week number in year (00-53); start week on Sunday.
%V: Week number in year (01-52); start week on Monday.
%W: Week number in year (00-53); start week on Monday.
%X: Country-specific time format based on locale.
%Y: Four-digit year (e.g., 1996).
%Z: Time zone name.

Strings for setting date

Strings for setting the date may be numeric or nonnumeric. Numeric strings consist of time, day, and year in the format MMDDhhmm[[CC]YY][.ss]. Nonnumeric strings may include month strings, time zones, a.m., and p.m.

time: A two-digit hour and two-digit minute (hhmm); hh uses 24-hour format.
day: A two-digit month and two-digit day of month (MMDD); default is current day and month.
year: The year specified as either the full four-digit century and year or just the two-digit year; the default is the current year.

Examples

Set the date to July 1 (0701), 4 a.m. (0400), 1995 (95):

date 0701040095

The command:

date +"Hello%t Date is %D %n%t Time is %T"

produces a formatted date as follows:

Hello     Date is 05/09/93
     Time is 17:53:39

dd options

Make a copy of an input file (if) using the specified conditions, and send the results to the output file (or standard output if of is not specified). Any number of options can be supplied, although if and of are the most common and are usually specified first. Because dd can handle arbitrary blocksizes, it is useful when converting between raw physical devices.

Options

bs=n

Set input and output blocksize to n bytes; this option overrides ibs and obs.

cbs=n

Set the size of the conversion buffer (logical record length) to n bytes. Use only if the conversion flag is ascii, ebcdic, ibm, block, or unblock.

conv=flags

Convert the input according to one or more (comma-separated) flags listed next. The first five flags are mutually exclusive.

ascii: EBCDIC to ASCII.
ebcdic: ASCII to EBCDIC.
ibm: ASCII to EBCDIC with IBM conventions.
block: Variable-length records (i.e., those terminated by a newline) to fixed-length records.
unblock: Fixed-length records to variable-length records.
lcase: Uppercase to lowercase.
ucase: Lowercase to uppercase.
noerror: Continue processing after read errors.
notrunc: Don't truncate output file.
swab: Swap each pair of input bytes.
sync: Pad input blocks to ibs with trailing zeros.

count=n

Copy only n input blocks.

ibs=n

Set input blocksize to n bytes (default is 512).

if=file

Read input from file (default is standard input).

obs=n

Set output blocksize to n bytes (default is 512).

of=file

Write output to file (default is standard output).

seek=n

Skip n output-sized blocks from start of output file.

skip=n

Skip n input-sized blocks from start of input file.

--help

Print help message and then exit.

--version

Print the version number and then exit.

You can multiply size values (n) by a factor of 1024, 512, or 2 by appending the letter k, b, or w, respectively. You can use the letter x as a multiplication operator between two numbers.

Examples

Convert an input file to all lowercase:

dd if=caps_file of=small_file conv=lcase

Retrieve variable-length data and write it as fixed-length to out:

data_retrieval_cmd | dd of=out conv=sync,block

deallocvt

deallocvt N

Deallocate and destroy the unused virtual console /dev/ttyN. Multiple consoles may be named with additional spaces and integers: deallocvt 1 4 will deallocate the /dev/tty1 and /dev/tty4. Consoles are considered unused if they are not in the foreground, have no open processes, and have no selected text. The command will not destroy consoles that are still active.

debugfs

debugfs [[option] device]

System administration command. Provide direct access to data structure of an ext2 filesystem in order to debug problems with the device. device is the special file corresponding to the device containing the ext2 filesystem (e.g., /dev/hda3). debugfs may be used on a mounted filesystem device.

Option

-b blocksize: Use the specified blocksize for the filesystem.
-c: Catastrophic mode. Open the filesystem in read-only mode, do not read the inode and group bitmaps initially.
-f file: Read commands from file. Exit when done executing commands.
-i: Specify file system device is an ext2 image file created by e2image.
-s block: Read the superblock from the specified block.
-w: Open the filesystem in read-write mode.
-R command: Execute the given command (see list below) then exit.
-V: Print version number, then exit.

Commands

cat file: Dump the contents of an inode to standard output.
cd directory: Change the current working directory to directory.
chroot directory: Change the root directory to be the specified inode.
close: Close the currently open filesystem.
clri file: Clear the contents of the inode corresponding to file.
dump file out_file: Dump the contents of an inode to out_file.
expand_dir directory: Expand directory.
feature [[-]feature]: Set filesystem feature listed on the command line, then print current feature settings. Use - to clear a feature.
find_free_block [goal]: Find first free block starting from goal (if specified) and allocate it.
find_free_inode [dir [mode]]: Find a free inode and allocate it.
freeb block: Mark block as not allocated.
freei file: Free the inode corresponding to file.
help: Print a list of commands understood by debugfs.
icheck block: Do block-to-inode translation.
initialize device blocksize: Create an ext2 filesystem on device.
kill_file file: Remove file and deallocate its blocks.
lcd directory: Change current working directory on native filesystem.
ln source_file dest_file: Create a link.
logdump [-ac] [-bblock] [-iinode] [-fjournal_file] [out_file]: Print the ext3 journal for the filesytem. Use options to specify the location of the journal by block, inode, or filename, or to specify a file to which the journal should be printed.
ls [-l] [-d] [pathname]: Emulate the ls command. Use -l for verbose format and -d to list deleted entries.
modify_inode file: Modify the contents of the inode corresponding to file.
mkdir directory: Make directory.
mknod file [p|[[c|b] major minor]]: Create a special device file.
ncheck inode: Do inode-to-name translation.
open [-b blocksize] [-c] [-f] [-i] [-w] [-s block] device: Open a filesystem.
pwd: Print the current working directory.
quit: Quit debugfs.
rdump directory dest_directory: Recursively dump directory and its contents to dest_directory on the native filesystem.
rm file: Remove file.
rmdir directory: Remove directory.
setb block: Mark block as allocated.
seti file: Mark in use the inode corresponding to file.
set_super_value [-l] field value: Set superblock field to value. Use -l to print a list of valid fields.
show_super_stats [-h]: List the contents of the superblock and block group descriptors. Use -h to list only the superblock contents.
stat file: Dump the contents of the inode corresponding to file.
testb block: Test whether block is marked as allocated.
testi file: Test whether the inode corresponding to file is marked as allocated.
unlink file: Remove a link.
write source_file file

depmod

depmod [options] modules

System administration command. Create a dependency file for the modules given on the command line. This dependency file can be used by modprobe to automatically load the relevant modules. The normal use of depmod is to include the line /sbin/depmod -a in one of the files in /etc/rc.d so that the correct module dependencies will be available after booting the system.

Options

-a, --all: Create dependencies for all modules listed in /etc/modules.conf.
-b dir, --basedir dir: Specify a base directory to use instead of /lib/modules.
-e, --errsyms: Print a list of all unresolved symbols.
-d: Debug mode. Show all commands being issued.
-h, --help: Print help message, then exit.
-n, --show: Write dependency file to standard output.
-q, --quiet: Don't display error messages about missing symbols.
-r, --root: Allow root to load modules not owned by root.
-s, --syslog: Write error messages to the syslog daemon instead of to standard error.
-v: Print a list of all processed modules.
-A, --quick: Check timestamps and update the dependency file if anything has changed.
-C file, --config file: Use the specified configuration file instead of /etc/modules.conf. May also be set using the MODULECONF environment variable.
-F file, --kernelsyms file: Use the specified kernel symbol file to build dependencies. Usually this is either a copy of a system's System.map file or the output of /proc/ksyms.
-V, --version: Print version number.

Files

/etc/modules.conf: Information about modules: which ones depend on others, and which directories correspond to particular types of modules.
/sbin/insmod, /sbin/rmmod: Programs that depmod relies on.

devdump

devdump isoimage

Interactively display the contents of the device or filesystem image isoimage. devdump displays the first 256 bytes of the first 2048-byte sector and waits for commands. The prompt shows the extent number (zone) and offset within the extent, and the contents display at the top of the screen.

Commands

+: Search forward for the next instance of the search string.
a: Search backward within the image.
b: Search forward within the image.
f: Prompt for a new search string.
g: Prompt for a new starting block and go there.
q: Exit.

df [options] [name]

Report the amount of free disk space available on all mounted filesystems or on the given name. (df cannot report on unmounted filesystems.) Disk space is shown in 1KB blocks (default) or 512-byte blocks (if the environment variable POSIXLY_CORRECT is set). name can be a device name (e.g., /dev/hd*), the directory name of a mounting point (e.g., /usr), or a directory name (in which case df reports on the entire filesystem in which that directory is mounted).

Options

-a, --all: Include empty filesystems (those with 0 blocks).
--block-size=n: Show space as n-byte blocks.
-h, --human-readable: Print sizes in a format friendly to human readers (e.g., 1.9G instead of 1967156).
-H, --si: Like -h, but show as power of 1000 rather than 1024.
-i, --inodes: Report free, used, and percent-used inodes.
-k, --kilobytes: Print sizes in kilobytes.
-l, --local: Show local filesystems only.
-m, --megabytes: Print sizes in megabytes.
--no-sync: Show results without invoking sync first (i.e., without flushing the buffers). This is the default.
-P, --portability: Use POSIX output format (i.e., print information about each filesystem on exactly one line).
--sync: Invoke sync (flush buffers) before getting and showing sizes.
-t type, --type=type: Show only type filesystems.
-T, --print-type: Print the type of each filesystem in addition to the sizes.
-x type, --exclude-type=type: Show only filesystems that are not of type type.
--help: Print help message and then exit.
--version: Print the version and then exit.

diff

diff [options] [diroptions] file1 file2

Compare two text files. diff reports lines that differ between file1 and file2. Output consists of lines of context from each file, with file1 text flagged by a < symbol and file2 text by a > symbol. Context lines are preceded by the ed command (a, c, or d) that would be used to convert file1 to file2. If one of the files is -, standard input is read. If one of the files is a directory, diff locates the filename in that directory corresponding to the other argument (e.g., diff my_dir junk is the same as diff my_dir/junk junk). If both arguments are directories, diff reports lines that differ between all pairs of files having equivalent names (e.g., olddir/program and newdir/program); in addition, diff lists filenames unique to one directory, as well as subdirectories common to both. See also cmp.

Options

-a, --text: Treat all files as text files. Useful for checking to see if binary files are identical.
-b, --ignore-space-change: Ignore repeating blanks and end-of-line blanks; treat successive blanks as one.
-B, --ignore-blank-lines: Ignore blank lines in files.
-c: Context diff: print 3 lines surrounding each changed line.
-C n, --context[=n]: Context diff: print n lines surrounding each changed line. The default context is 3 lines.
-d, --minimal: To speed up comparison, ignore segments of numerous changes and output a smaller set of changes.
-D symbol, --ifdef=symbol: When handling C files, create an output file that contains all the contents of both input files, including #ifdef and #ifndef directives that reflect the directives in both files.
-e, --ed: Produce a script of commands (a, c, d) to re-create file2 from file1 using the ed editor.
-F regexp, --show-function-line[=regexp]: For context and unified diff, show the most recent line containing regexp before each block of changed lines.
-H: Speed output of large files by scanning for scattered small changes; long stretches with many changes may not show up.
--help: Print brief usage message.
--horizon-lines=n: In an attempt to find a more compact listing, keep n lines on both sides of the changed lines when performing the comparison.
-i, --ignore-case: Ignore case in text comparison. Uppercase and lowercase are considered the same.
-I regexp, --ignore-matching-lines=regexp: Ignore lines in files that match the regular expression regexp.
-l, --paginate: Paginate output by passing it to pr.
-L label, --label label, --label=label: For context and unified diff, print label in place of the filename being compared. The first such option applies to the first filename and the second option to the second filename.
--left-column: For two-column output (-y), show only left column of common lines.
-n, --rcs: Produce output in RCS diff format.
-N, --new-file: Treat nonexistent files as empty.
-p, --show-c-function: When handling files in C or C-like languages such as Java, show the function containing each block of changed lines. Assumes -c, but can also be used with a unified diff.
-P, --unidirectional-new-file: If two directories are being compared and the first lacks a file that is in the second, pretend that an empty file of that name exists in the first directory.
-q, --brief: Output only whether files differ.
-r, --recursive: Compare subdirectories recursively.
-s, --report-identical-files: Indicate when files do not differ.
-S filename, --starting-file=filename: For directory comparisons, begin with the file filename, skipping files that come earlier in the standard list order.
--suppress-common-lines: For two-column output (-y), do not show common lines.
-t, --expand-tabs: Produce output with tabs expanded to spaces.
-T, --initial-tab: Insert initial tabs into output to line up tabs properly.
-u: Unified diff: print old and new versions of lines in a single block, with 3 lines surrounding each block of changed lines.
-U n, --unified[=n]: Unified diff: print old and new versions of lines in a single block, with n lines surrounding each block of changed lines. The default context is 3 lines.
-v, --version: Print version number of this version of diff.
-w, --ignore-all-space: Ignore all whitespace in files for comparisons.
-W n, --width=n: For two-column output (-y), produce columns with a maximum width of n characters. Default is 130.
-x regexp, --exclude=regexp: Do not compare files in a directory whose names match regexp.
-X filename, --exclude-from=filename: Do not compare files in a directory whose names match patterns described in the file filename.
-y, --side-by-side: Produce two-column output.
-n

diff3

diff3 [options] file1 file2 file3

Compare three files and report the differences. No more than one of the files may be given as - (indicating that it is to be read from standard input). The output is displayed with the following codes:

= = = =: All three files differ.
= = = =1: file1 is different.
= = = =2: file2 is different.
= = = =3: file3 is different.

diff3 is also designed to merge changes in two differing files based on a common ancestor file (i.e., when two people have made their own set of changes to the same file). diff3 can find changes between the ancestor and one of the newer files and generate output that adds those differences to the other new file. Unmerged changes occur where both of the newer files differ from each other and at least one of them differs from the ancestor. Changes from the ancestor that are the same in both of the newer files are called merged changes. If all three files differ in the same place, it is called an overlapping change.

This scheme is used on the command line with the ancestor being file2, the second filename. Comparison is made between file2 and file3, with those differences then applied to file1.

Options

-3, --easy-only: Create an ed script to incorporate into file1 unmerged, nonoverlapping differences between file1 and file3.
-a, --text: Treat files as text.
-A, --show-all: Create an ed script to incorporate all changes, showing conflicts in bracketed format.
-e, --ed: Create an ed script to incorporate into file1 all unmerged differences between file2 and file3.
-E, --show-overlap: Create an ed script to incorporate unmerged changes, showing conflicts in bracketed format.
-x, --overlap-only: Create an ed script to incorporate into file1 all differences where all three files differ (overlapping changes).
-X: Same as -x, but show only overlapping changes, in bracketed format.
-m, --merge: Create file with changes merged (not an ed script).
-L label, --label=label: Use label to replace filename in output.
-i: Append the w (save) and q (quit) commands to ed script output.
-T, --initial-tab: To line tabs up properly in output, begin lines with a tab instead of two spaces.
-v, --version: Print version information and then exit.

dig

dig [@server] [options] [name] [type] [class] [query-options]
dig @server name type
dig -h

The dig command is used to query DNS servers; it is more flexible than the deprecated nslookup command. If you use it without any options or arguments, it will search for the root server. The standard arguments are:

server: The server to query. If no server is supplied, dig will check the name servers listed in /etc/resolv.conf. The address may be an IPv4 dotted address or an IPv6 colon-delimited address. It may also be a hostname, which dig will resolve (through the name servers in /etc/resolv.conf).
name: The domain name to look up.
type: The type of query to perform, such as A, ANY, MX, SIG, and so forth. The default is A, but you may use any valid BIND9 query type.

Options

You may use the following option flags with dig:

-b address: Set the source IP address for the query.
-c class: Set the class of query. The default value is IN (internet), but you can choose HS for Hesiod or CH for CHAOSNET.
-f filename: Operate in batch mode, performing the queries in the file you specify.
-p portnumber: Choose the port number for the query. The default value is the standard DNS port, 53.
-t type: Set the type of query, as with the query argument. The default value is A, but you may use any valid BIND9 query.
-x addr: Use the -x flag for reverse lookups, specifying an IPv4 or IPv6 address. You do not need the name, class, or type arguments if you use the -x flag.
-k filename: Specify a TSIG key file; used for signed transactions. You can also use the -y key, although this is less secure.
-y keyname:keyvalue: Enter the actual key name and value when conducting a signed transaction. Because the key and value can be seen in the output of ps, this is not recommended for use on multiuser systems; use -k instead.

Query options

There are a large number of query options for dig. Each query option is preceded by +, and many have an opposite version beginning with no. For example, the tcp flag is passed as +tcp, and negated with +notcp. Because there are so many options, only a few are discussed here. For greater detail, see the dig manpage.

+tcp, +notcp: Use (or do not use) the TCP protocol instead of the default UDP.
+domain=searchdomain: Perform a search in the domain specified; this is equivalent to using the +search option and having "searchdomain" as the sole entry in the search list or domain directive of /etc/resolv.conf.
+search, +nosearch: Use (or do not use) the search list provided in /etc/resolv.conf. The default is not to use the search list.
+time=T: Timeout for queries, in seconds. The default is 5, and the minimum is 1.
+tries=N: The number of times to retry UDP queries. The default is 3, and the minimum is 1.

dip

dip [options] [chat scriptfile]

System administration command. Set up or initiate dial-up Internet connections. dip can be used to establish connections for users dialing out or dialing in. Commands can be used in interactive mode or placed in a script file for use in dial-out connections. To establish dial-in connections, dip is often used as a shell, and may be executed using the commands diplogin or diplogini.

Options

-a: In dial-in mode, prompt for username and password. Same as the diplogini command.
-i: Initiate a login shell for a dial-in connection. Same as the diplogin command.
-k: Kill the most recent dip process or the process running on the device specified by the -l option.
-l device: Used with the -k option. Specifies a tty device.
-m mtu: Maximum Transfer Unit. The default is 296.
-p protocol: The protocol to use: SLIP, CSLIP, PPP, or TERM.
-t: Command mode. This is usually done for testing.
-v: Verbose mode.

Commands

Most of these commands can be used either in interactive mode or in a script file.

beep times: Beep the terminal the specified number of times.
bootp: Retrieve local and remote IP addresses using the BOOTP protocol.
break: Send a BREAK.
chatkey keyword code: Map a modem response keyword to a numeric code.
config [interface|routing] [pre|up|down|post] arguments: Modify interface characteristics or the routing table before the link comes up, when it is up, when it goes down, or after it is down. The syntax for arguments is the same as for arguments for the ifconfig or route commands.
databits 7|8: Set the number of data bits.
dec $variable [value]: Decrement $variable by value. The default is 1.
default: Set default route to the IP address of the host connected to.
dial phonenumber [timeout]: Dial phonenumber. Abort if remote modem doesn't answer within timeout seconds. Set $errlvl according to the modem response.
echo on|off: Enable or disable the display of modem commands.
exit [n]: Exit the script. Optionally return the number n as the exit status.
flush: Clear the input buffer.
get $variable [ask|remote [timeout]] value: Set $variable to value. If ask is specified, prompt the user for a value. If remote is specified, retrieve the value from the remote system. Abort after timeout seconds.
goto label: Jump to the section identified by label.
help: List available commands.
if expr goto label: Jump to the section identified by label if the expression evaluates to true. An expression compares a variable to a constant using one of these operators: =, !=, <, >, <=, or >=.
inc $variable [value]: Increment $variable by value. The default is 1.
init string: Set the string used to initialize the modem. The default is ATE0 Q0 V1 X1.
mode protocol: Set the connection protocol. Valid values are SLIP, CSLIP, PPP, and TERM. The default is SLIP.
netmask mask: Set the subnet mask.
parity E|O|N: Set the line parity to even, odd, or none.
password: Prompt user for password.
proxyarp: Install a proxy ARP entry in the local ARP table.
print $variable: Display the content of $variable.
psend command: Execute command in a shell, and send output to the serial device. Commands are executed using the user's real UID.
port device: Specify the serial device the modem is attached to.
quit: Exit with a nonzero exit status. Abort the connection.
reset: Reset the modem.
securid: Prompt user for the variable part of an ACE System SecureID password, and send it together with the stored prefix to the remote system.
securidf prefix: Store the fixed part of an ACE System SecureID password.
send string: Send string to the serial device.
shell command: Execute command in a shell using the user's real UID.
skey [timeout]: Wait for an S/Key challenge, then prompt user for the secret key. Generate and send the response. Abort if challenge is not received within timeout seconds. S/Key support must be compiled into dip.
sleep time: Wait time seconds.
speed bits-per-second: Set the port speed. Default is 38400.
stopbits 1|2: Set the number of stop bits.
term: Enable terminal mode. Pass keyboard input directly to the serial device.
timeout time: Set the number of seconds the line can be inactive before the link is closed.
wait text [timeout]

dir

dir [options] [file]

List directory contents. dir is equivalent to the command ls -C -b (list files in columns, sorted vertically, special characters escaped) and it takes the same arguments as ls. This is an alternate invocation of the ls command and is provided for the convenience of those converting from Microsoft Windows and the DOS shell.

dircolors

dircolors [options] [file]

Set the color options for ls by changing the LS_COLORS environment variable. If you specify a file, dircolors will read it to determine which colors to use. Otherwise, it will use a default set of colors.

Options

The program takes three options in addition to the standard --help and --version flags:

-p, --print-database: Display the default colors. You can copy this information into a file and change it to suit your preferences, and then run the program with the file as its argument to set the colors to your new values.
-c, --csh, --c-shell: Use csh (C shell) syntax when setting the LS_COLORS variable.
-b, --sh, --bourne-shell: Use the Bourne shell syntax when setting the LS_COLORS variable.

dirname

dirname pathname

Print pathname, excluding the last level. Useful for stripping the actual filename from a pathname. If there are no slashes (no directory levels) in pathname, dirname prints . to indicate the current directory. See also basename.

dmesg

dmesg [options]

System administration command. Display the system control messages from the kernel ring buffer. This buffer stores all messages since the last system boot, or the most recent ones if the buffer has been filled.

Options

-c: Clear buffer after printing messages.
-nlevel: Set the level of system message that will display on console.
-sbuffersize: Specify buffersize of kernel ring buffer. This is useful if you have changed the kernel default.

dnsdomain-name

dnsdomainname

TCP/IP command. Print the system's DNS domain name. See also hostname.

dnssec-keygen

dnssec-keygen [options] domain-name

System administration command. Generate encrypted Secure DNS (DNSSEC) or Transaction Signatures (TSIG) keys for domain-name. When the key is completed, dnssec-keygen prints the key identifier to standard output and creates public and private key files whose names are based on the key identifier and the filename extensions .key and .private. It creates both files even when using an asymmetric algorithm like HMAC-MD5. For more information on Secure DNS, see DNS and BIND (O'Reilly), or read RFC 2535.

Options

-a algorithm: Specify the cryptographic algorithm to use. Accepted values are RSAMD5, RSA, DSA, DH, or HMAC-MD5.
-b bitsize: Specify the key bitsize. Accepted values depend on the encryption algorithm used.
-c class: The domain record for which the key is being generated should contain class. When this option is not given, a class of IN is assumed.
-e: Use a large exponent when generating an RSA key.
-g generator: Specified the number to use as a generator when creating a DH (Diffie Hellman) key. Accepted values are 2 and 5.
-h: Print a help message, then exit.
-n type: The owner of the key must be of the specified type. Accepted values are ZONE, HOST, ENTITY, or USER.
-p protocol: Specify the protocol value for the generated key. Accepted values are given in RFC 2535 and other DNS Security RFCs. By default the value is either 2 (email) or 3 (DNSSEC).
-r device: Specify the device to use as a source of randomness when creating keys. This can be a device file, a file containing random data, or the string keyboard to specify keyboard input. By default, /dev/random will be used when available, and keyboard input will be used when it is not.
-s type: Specify whether the key can be used for authentication, confirmation, both, or neither. Accepted values for type are AUTHCONF, NOAUTHCONF, NOAUTH, or NOCONF.

dnssec-makekeyset

dnssec-makekeyset [options] key-identifiers

System administration command. Generate a domain keyset from one or more DNS Security keys generated by dnssec-keygen. Keysets can be sent to parent zone administrators to be signed with the zone key. The keyset is written to a file with the name keyset-domainname. For more information on Secure DNS, see DNS and BIND (O'Reilly), or read RFC 2535.

Options

-a: Verify all generated signatures.
-e end-time: Specify the date and time the records will expire. The end-time may be specified in yyyymmddhhmmss notation, or as +N seconds from the start-time. The default is 30 days from start-time.
-h: Print help message, then exit.
-p: Use pseudo-random data to sign the zone key.
-r device: Specify the device to use as a source of randomness when creating keys. This can be a device file, a file containing random data, or the string keyboard to specify keyboard input. By default, /dev/random will be used when available, and keyboard input will be used when it is not.
-s start-time: Specify the date and time the records become valid. The end-time may be specified in yyyymmddhhmmss notation, or as +N seconds from the current time. The default is the current time.
-t ttl: Specify the TTL (time to live) in seconds for the KEY and SIG records. Default is 3600 seconds.

dnssec-signkey

dnssec-signkey [options] keyset key-identifiers

System administration command. Sign a secure DNS keyset with the key signatures specified in the list of key-identifiers. A zone administrator would use this command to sign a child zone's keyset with the parent zone's keys. For more information on Secure DNS, see DNS and BIND (O'Reilly), or read RFC 2535.

Options

-a: Verify generated signatures.
-c class: Specify the DNS class of the keyset.
-e end-time: Specify the date and time the records will expire. The end-time may be specified in yyyymmddhhmmss notation, or as +N seconds from the start-time. The default is 30 days from start-time.
-h: Print help message, then exit.
-p: Use pseudo-random data to sign the zone key.
-r device: Specify the device to use as a source of randomness when creating keys. This can be a device file, a file containing random data, or the string keyboard to specify keyboard input. By default, /dev/random will be used when available, and keyboard input will be used when it is not.
-s start-time: Specify the date and time the records become valid. The end-time may be specified in yyyymmddhhmmss notation, or given as +N seconds from the current time. The default is the current time.

dnssec-signzone

dnssec-signzone [options] zonefile [key-identifiers]

System administration command. Sign a secure DNS zonefile with the signatures in the specified list of key-identifiers. If signed keysets associated with the zone are found in the current directory, include their signatures in the signed zone file. The dnssec-signzone command writes the signed zone information to a file named db-domainname.signed. This file should be referenced in a zone statement in a named.conf file. For more information on Secure DNS, see DNS and BIND (O'Reilly), or read RFC 2535.

Options

-a: Verify generated signatures.
-c class: Specify the DNS class of the keyset.
-d directory: Search directory for signed key files.
-e end-time: Specify the date and time the records will expire. The end-time may be specified in yyyymmddhhmmss notation, or given as +N seconds from the start-time. The default is 30 days from start-time.
-h: Print help message, then exit.
-i days: When signing a previously signed zone, replace any records due to expire within the specified number of days. The default is one quarter of the number of days between the signature's start-time and end-time.
-n threads: Specify the number of threads to use when signing the zone file. The default is one for each detected CPU.
-o origin: Specify the zone origin. The name of the zone file is the default origin.
-p: Use pseudo-random data to sign the zone key.
-r device: Specify the device to use as a source of randomness when creating keys. This can be a device file, a file containing random data, or the string keyboard to specify keyboard input. By default, /dev/random will be used when available, and keyboard input will be used when it is not.
-s start-time: Specify the date and time the records become valid. The end-time may be specified in yyyymmddhhmmss notation, or given as +N seconds from the current time. The default is the current time.
-t: Print statistics when complete.

domainname

domainname [name]

NFS/NIS command. Set or display name of current NIS domain. With no argument, domainname displays the name of the current NIS domain. Only a privileged user can set the domain name by giving an argument; this is usually done in a startup script.

dosfsck

dosfsck [options] device
fsck.msdos [options] device

System administration command. Similar to fsck, but specifically intended for MS-DOS filesystems. When checking an MS-DOS filesystem, fsck calls this command. Normally dosfsck stores all changes in memory, then writes them when checks are complete.

Options

-a: Automatically repair the system; do not prompt the user.
-d file: Drop the named file from the file allocation table. Force checking, even if kernel has already marked the filesystem as valid. dosfsck will normally exit without checking if the system appears to be clean.
-f: Save unused cluster chains to files.
-l: List pathnames of files being processed.
-r: Repair the system, prompting user for advice.
-t: Mark unreadable clusters as bad.
-u file: Attempt to undelete the named file.
-v: Verbose mode.
-w: Write changes to disk immediately.
-y: When queried, answer "yes."
-A: Filesystem is an Atari version of MS-DOS.
-F: Flush buffer caches before checking.
-V: Repeat test to verify all errors have been corrected.

du [options] [directories]

Print disk usage (as the number of 1KB blocks used by each named directory and its subdirectories; default is the current directory).

Options

-a, --all: Print disk usage for all files, not just subdirectories.
-b, --bytes: Print sizes in bytes.
-c, --total: In addition to normal output, print grand total of all arguments.
-D, --dereference-args: Follow symbolic links, but only if they are command-line arguments.
-h, --human-readable: Print sizes in human-readable format.
-H, --si: Like -h, but show as power of 1000 rather than 1024.
-k, --kilobytes: Print sizes in kilobytes (this is the default).
-l, --count-links: Count the size of all files, whether or not they have already appeared (i.e., via a hard link).
-L, --dereference: Follow symbolic links.
--exclude=pattern: Exclude files that match pattern.
--max-depth=num: Report sizes for directories only down to num levels below the starting point (which is level 0).
-m, --megabytes: Print sizes in megabytes.
-s, --summarize: Print only the grand total for each named directory.
-S, --separate-dirs: Do not include the sizes of subdirectories when totaling the size of parent directories.
-x, --one-file-system: Display usage of files in current filesystem only.
-X, --exclude-from=file: Exclude files that match any pattern in file.
--help: Print help message and then exit.
--version: Print the version and then exit.

dumpe2fs

dumpe2fs device

System administration command. Print information about device's superblock and blocks group.

Options

-b: List blocks marked as bad.
-f: Force display of filesystems with unknown feature flags.
-h: Display superblock information only.
-i: Specify device is an image file created by e2image.
-ob superblock: Specify location of the superblock.
-oB blocksize: Specify blocksize to use when examining filesystem.
-x: Print block numbers in hexadecimal.
-V: Print version number and exit.

dumpkeys

dumpkeys [options]

Print information about the keyboard driver's translation tables to standard output. Further information is available in the manual pages under keytables.

Options

-1, --separate-lines

Print one line for each modifier/keycode pair and prefix plain to each unmodified keycode.

-ccharset, --charset=charset

Specify character set with which to interpret character code values. The default character set is iso-8859-1. The full list of valid character sets is available with the --help option.

--compose-only

Print compose key combinations only. Requires compose key support in the kernel.

-f, --full-table

Output in canonical, not short, form: for each key, print a row with modifier combinations divided into columns.

--funcs-only

Print function key string definitions only; do not print key bindings or string definitions.

-h, --help

Print help message and the version.

-i, --short-info

Print in short-info format, including information about acceptable keycode keywords in the keytable files; the number of actions that can be bound to a key; a list of the ranges of action codes (the values to the right of a key definition); and the number of function keys that the kernel supports.

--keys-only

Print key bindings only; do not print string definitions.

-l, --long-info

Print the same information as in --short-info, plus a list of the supported action symbols and their numeric values.

-n, --numeric

Print action code values in hexadecimal notation; do not attempt to convert them to symbolic notation.

-S num, --shape=num

Print using num to determine table shape. Values of num are:

0: Default.
1: Same as --full-table.
2: Same as --separate-lines.
3: One line for each keycode up to the first hole, then one line per modifier/keycode pair.

e2fsck

e2fsck [options] device
fsck.ext2 [options] device

System administration command. Similar to fsck, but specifically intended for Linux Second Extended Filesystems. When checking a second extended filesystem, fsck calls this command. This command is also used for the third extended filesystem (ext3), which is a journaling version of the second extended filesystem.

Options

-b superblock: Use superblock instead of the default superblock.
-d: Debugging mode.
-f: Force checking, even if kernel has already marked the filesystem as valid. e2fsck will normally exit without checking if the system appears to be clean.
-l file: Consult file for a list of bad blocks, in addition to checking for others.
-n: Ensure that no changes are made to the filesystem. When queried, answer "no."
-p: "Preen." Repair all bad blocks noninteractively.
-t: Display timing statistics.
-v: Verbose.
-y: When queried, answer "yes."
-B size: Expect to find the superblock at size; if it's not there, exit.
-F: Flush buffer caches before checking.
-L file: Consult file for list of bad blocks instead of checking filesystem for them.

e2image

e2image [option] device file

System administration command. Store disaster recovery data for ext2 filesystem on device to image file file. Weekly filesystem images can be an important part of a disaster recovery plan.

Option

-r: Create a raw image file that can be checked and debugged using filesystem utilities such as e2fsck or debugfs. Raw images are created as sparse files. Either compress the image file before moving it, or use the -sparse=always option when copying it with cp.

e2label

e2label device [label]

System administration command. Display the filesystem label on an ext2 filesystem device. Change filesystem label to label if specified.

echo

echo [options] [string]

Send (echo) the input string to standard output. This is the /bin/echo command. echo also exists as a command built into the C shell and bash. The following character sequences have special meanings:

\a: Alert (bell).
\b: Backspace.
\c: Suppress trailing newline.
\f: Form feed.
\n: Newline.
\r: Carriage return.
\t: Horizontal tab.
\v: Vertical tab.
\\: Literal backslash.
\nnn: The octal character whose ASCII code is nnn.

Options

-e: Enable character sequences with special meaning. (In some versions, this option is not required in order to make the sequences work.)
-E: Disable character sequences with special meaning.
-n: Suppress printing of newline after text.
--help: Print help message and then exit.
--version: Print version information and then exit.

Examples

/bin/echo "testing printer" | lp
/bin/echo "TITLE\nTITLE" > file ; cat doc1 doc2 >> file
/bin/echo "Warning: ringing bell \a"

egrep

egrep [options] [regexp] [files]

Search one or more files for lines that match an extended regular expression regexp. egrep doesn't support the regular expressions $, $, \n, \<, \>, \{, or \}, but does support the other expressions, as well as the extended set +, ?, |, and ( ). Remember to enclose these characters in quotes. Regular expressions are described in Chapter 9. Exit status is 0 if any lines match, 1 if none match, and 2 for errors.

See grep for the list of available options. Also see fgrep.

Examples

Search for occurrences of Victor or Victoria in file:

egrep 'Victor(ia)*' file
egrep '(Victor|Victoria)' file

Find and print strings such as old.doc1 or new.doc2 in files, and include their line numbers:

egrep -n '(old|new)\.doc?' files

eject

eject [options] [device]

Eject removable media such as a CD-ROM, floppy, tape, or JAZ or ZIP disk. You may name the device by /dev or /mnt filename. The /dev and /mnt prefixes are optional for any items in the /dev and /mnt directories. If no device is named, it is assumed that "cdrom" should be ejected.

Options

The eject command takes the following option flags:

-h: Display help information.
-v, --verbose: Verbose mode: display additional information about actions.
-d, --default: List the default device name rather than doing anything.
-a, --auto on|1|off|0: Set the auto-eject mode to on or off (equivalent to 1 or 0). If auto-eject mode is on, the device is ejected when closed or unmounted.
-c, --changerslot slotnumber: If using a CD-ROM changer, select a CD from one of the slots. Slots are enumerated starting with 0, and the CD-ROM drive must not be playing music or mounted to read data.
-t, --trayclose: Close the CD-ROM drive. Not all drives will respond to this command.
-x, --cdspeed speed: Set the speed multiplier for the CD-ROM to an integer, usually a power of 2. Not all devices support this command. Setting the speed to 0 indicates that the drive should operate at its maximum speed.
-n, --noop: Do not perform any actions; merely display the actions that would be performed.
-r, --cdrom: Use CD-ROM commands to eject the drive. Normally, the system will try all methods (CD-ROM, SCSI, floppy, tape) to eject.
-s, --scsi: Use SCSI commands to eject the drive. Normally, the system will try all methods (CD-ROM, SCSI, floppy, tape) to eject.
-f, --floppy: Use floppy commands to eject the drive. Normally, the system will try all methods (CD-ROM, SCSI, floppy, tape) to eject.
-q, --tape: Use tape commands to eject the drive. Normally, the system will try all methods (CD-ROM, SCSI, floppy, tape) to eject.
-p, --proc: Use the mounted files listed in /proc/mounts rather than in /etc/mtab.
-V, --version: Display version information, then quit.

elvtune

elvtune [options] devices

System administration command. Set the latency in the elevator algorithm used to schedule I/O activities for the specified block devices. If no options are given, print the current settings for devices.

Options

-b N: Set the maximum coalescing factor allowed on writes when reads are pending to N.
-h: Print help message, then exit.
-r N: Set the maximum read latency (basically, the number of sectors to read before writes are allowed) to N. The default is 8192.
-v: Print version number, then exit.
-w N: Set the maximum write latency (sectors to write before allowing a read) to N. The default is 16384.

emacs

emacs [options] [files]

A text editor and all-purpose work environment. For more information, see Chapter 10.

env

env [option] [variable=value ... ] [command]

Display the current environment or, if an environment variable is specified, set it to a new value and display the modified environment. If command is specified, execute it under the modified environment.

Options

-, -i, --ignore-environment: Ignore current environment entirely.
-u name, --unset name: Unset the specified variable.
--help: Print help message and then exit.
--version: Print version information and then exit.

etags

etags [options] files

Create a list of function and macro names defined in a programming source file. etags generates tags for use by emacs. (ctags produces an equivalent tags file for use with vi.) More than one file may be specified. etags understands many programming languages, including C, C++, FORTRAN, Java, Perl, Python, flex, yacc, and bison. The output list (named TAGS by default) contains lines of the form:

name     file     context

M-x visit-tags-table

You will be prompted for the name of the tag table; the default is TAGS. To switch to the source file associated with the name listed in tagsfile, type:

M-x find-tag

You will be prompted for the tag you would like Emacs to search for.

Options

-a, --append: Append tag output to existing list of tags.
-d, --defines: Include tag entries for C preprocessor definitions.
-i file, --include=file: Add a note to the tags file that file should be consulted in addition to the normal input file.
-l language, --language=language: Consider the files that follow this option to be written in language. Use the -h option for a list of languages and their default filename extensions.
-o file, --output=file: Write to file.
-r regexp, --regex=regexp: Include a tag for each line that matches regexp in the files following this option.
-C, --c++: Expect .c and .h files to contain C++, not C, code.
-D, --no-defines: Do not include tag entries for C preprocessor definitions.
-H, -h, --help: Print usage information.
-R, --noregex: Don't include tags based on regular-expression matching for the files that follow this option.
-S, --ignore-indentation: Normally etags uses indentation to parse the tag file; this option tells it to rely on it less.
-V, --version: Print the version number.

ex [options] file

An interactive command-based editor. For more information, see Chapter 11.

expand

expand [options] [files]

Convert tabs in given files (or standard input, if the file is named -) to appropriate number of spaces; write results to standard output.

Options

-tabs, -t tabs, --tabs tabs: tabs is a comma-separated list of integers that specify the placement of tab stops. If exactly one integer is provided, the tab stops are set to every integer spaces. By default, tab stops are 8 spaces apart. With -t and --tabs, the list may be separated by whitespace instead of commas.
-i, --initial: Convert tabs only at the beginning of lines.
--help: Print help message and then exit.
--version: Print version information and then exit.

expr

expr arg1 operator arg2 [ operator arg3 ... ]

Evaluate arguments as expressions and print the results. Arguments and operators must be separated by spaces. In most cases, an argument is an integer, typed literally or represented by a shell variable. There are three types of operators: arithmetic, relational, and logical, as well as keyword expressions. Exit status for expr is 0 (expression is nonzero and nonnull), 1 (expression is 0 or null), or 2 (expression is invalid).

Arithmetic operators

Use these to produce mathematical expressions whose results are printed:

+: Add arg2 to arg1.
-: Subtract arg2 from arg1.
*: Multiply the arguments.
/: Divide arg1 by arg2.
%: Take the remainder when arg1 is divided by arg2.

Addition and subtraction are evaluated last, unless they are grouped inside parentheses. The symbols *, (, and ) have meaning to the shell, so they must be escaped (preceded by a backslash or enclosed in single quotes).

Relational operators

Use these to compare two arguments. Arguments can also be words, in which case comparisons are defined by the locale. If the comparison statement is true, the result is 1; if false, the result is 0. Symbols > and < must be escaped.

=, = =: Are the arguments equal?
!=: Are the arguments different?
>: Is arg1 greater than arg2?
>=: Is arg1 greater than or equal to arg2?
<: Is arg1 less than arg2?
<=: Is arg1 less than or equal to arg2?

Logical operators

Use these to compare two arguments. Depending on the values, the result can be arg1 (or some portion of it), arg2, or 0. Symbols | and & must be escaped.

|: Logical OR; if arg1 has a nonzero (and nonnull) value, the result is arg1; otherwise, the result is arg2.
&: Logical AND; if both arg1 and arg2 have a nonzero (and nonnull) value, the result is arg1; otherwise, the result is 0.
:: Like grep; arg2 is a pattern to search for in arg1. arg2 must be a regular expression. If part of the arg2 pattern is enclosed in  (escaped parentheses), the result is the portion of arg1 that matches; otherwise, the result is simply the number of characters that match. By default, a pattern match always applies to the beginning of the first argument (the search string implicitly begins with a ^). Start the search string with .* to match other parts of the string.

Keywords

index string character-list: Return the first position in string that matches the first possible character in character-list. Continue through character-list until a match is found, or return 0.
length string: Return the length of string.
match string regex: Same as string : regex.
quote token: Treat token as a string, even if it would normally be a keyword or an operator.
substr string start length: Return a section of string, beginning with start, with a maximum length of length characters. Return null when given a negative or nonnumeric start or length.

Examples

Division happens first; result is 10:

expr 5 + 10 / 2

Addition happens first; result is 7 (truncated from 7.5):

expr \( 5 + 10 \) / 2

Add 1 to variable i. This is how variables are incremented in shell scripts:

i=`expr $i + 1`

Print 1 (true) if variable a is the string "hello":

expr $a = hello

Print 1 (true) if b plus 5 equals 10 or more:

expr $b + 5 \>= 10

Find the 5th, 6th, and 7th letters of the word character:

expr substr character 5 3

In the examples that follow, variable p is the string "version.100". This command prints the number of characters in p:

expr $p : '.*'           Result is 11

Match all characters and print them:

expr $p : '\(.*\)'       Result is "version.100"

Print the number of lowercase letters at the beginning of p:

expr $p : '[a-z]*'       Result is 7

Match the lowercase letters at the beginning of p:

expr $p : '\([a-z]*\)'   Result is "version"

Truncate $x if it contains five or more characters; if not, just print $x. (Logical OR uses the second argument when the first one is 0 or null, i.e., when the match fails.)

expr $x : '\(.....\)' \| $x

In a shell script, rename files to their first five letters:

mv $x `expr $x : '\(.....\)' \| $x`

(To avoid overwriting files with similar names, use mv -i.)

false

false

A null command that returns an unsuccessful (nonzero) exit status. Normally used in bash scripts. See also true.

fdformat

fdformat [option] device

Low-level format of a floppy disk. The device for a standard format is usually /dev/fd0 or /dev/fd1.

Option

-n: Do not verify format after completion.

fdisk

fdisk [options] [device]

System administration command. Maintain disk partitions via a menu. fdisk displays information about disk partitions, creates and deletes disk partitions, and changes the active partition. It is possible to assign a different operating system to each of the four possible primary partitions, though only one partition is active at any given time. You can also divide a physical partition into several logical partitions. The minimum recommended size for a Linux system partition is 40MB. Normally, device will be /dev/hda, /dev/hdb, /dev/sda, /dev/sdb, /dev/hdc, /dev/hdd, and so on. See also cfdisk.

Options

-b sectorsize: Set the size of individual disk sectors. May be 512, 1024, or 2048. Most systems now recognize sector sizes, so this is not necessary.
-l: List partition tables and exit.
-u: Report partition sizes in sectors instead of cylinders.
-s partition: Display the size of partition, unless it is a DOS partition.
-v: Print version number, then exit.

Commands

a: Toggle a bootable flag on current partition.
b: Edit disklabel of a BSD partition.
c: Toggle DOS compatibility flag.
d: Delete current partition.
l: List all partition types.
m: Main menu.
n: Create a new partition; prompt for more information.
o: Create an empty DOS partition table.
p: Print a list of all partitions and information about each.
q: Quit; do not save.
t: Replace the type of the current partition.
u: Modify the display/entry units, which must be cylinders or sectors.
v: Verify: check for errors, and display a summary of the number of unallocated sectors.
w: Save changes and exit.
x: Switch to expert commands.

fetchmail

fetchmail [options] [servers...]

System administration command. Retrieve mail from mail servers and forward it to the local mail delivery system. fetchmail retrieves mail from servers that support the common mail protocols POP2, POP3, IMAP2bis, and IMAP4. Messages are delivered via SMTP through port 25 on the local host and through your system's mail delivery agent (such as sendmail), where they can be read through the user's mail client. fetchmail settings are stored in the ~/.fetchmailrc file. Parameters and servers can also be set on the command line, which will override settings in the .fetchmailrc file. fetchmail is compatible with the popclient program, and users can use both without having to adjust file settings.

Options

-a, --all

Retrieve all messages from server, even ones that have already been seen but are left on the server. The default is to retrieve only new messages.

-auth type

Specify an authentication type. type can be: password, kerberos_v5, kerberos, gssapi, cram-md5, otp, ntlm, ssh, or any. When using the default value, any, fetchmail will use the highest authentication available. In decreasing order of security: gssapi, kerberos, cram, x-otp, ntlm, then login. Using ssh suppresses authentication. Use ssh when using an end-to-end secure connection.

-B n, --fetchlimit n

Set the maximum number of messages (n) accepted from a server per query.

-b n, --batchlimit n

Set the maximum number of messages sent to an SMTP listener per connection. When this limit is reached, the connection will be broken and reestablished. The default of 0 means no limit.

-bsmtp file

Append fetched mail to the specified batched sendmail (BSMTP) file. If file is -, send to standard output.

-c, --check

Check for mail on a single server without retrieving or deleting messages. Works with IMAP, but not well (if at all) with other protocols.

-D [domain], --smtpaddress [domain]

Specify the domain name placed in RCPT TO lines sent to SMTP. The default is the local host.

-d n, --daemon n

Detach from current process and run as a daemon, fetching mail every n seconds. A user may run only one fetchmail daemon process. See option --quit.

-E header, --envelope header

Change the header assumed to contain the mail's envelope address (usually "X-Envelope-to:") to header.

-e n, --expunge n

Tell an IMAP server to EXPUNGE (i.e., purge messages marked for deletion) after n deletes. A setting of 0 indicates expunging only at the end of the session. Normally, an expunge occurs after each delete.

-F, --flush

For POP3 and IMAP servers, remove previously retrieved messages from the server before retrieving new ones.

-f file, --fetchmailrc file

Specify a nondefault name for the fetchmail configuration file.

--fetchdomains hosts

Specify the domains to which mail should be sent when operating in ETRN or ODMR mode.

-I specification, --interface specification

Require that the mail server machine is up and running at a specified IP address (or range) before polling. The specification is given as interface/ipaddress/mask. The first part indicates the type of TCP connection expected (sl0, ppp0, etc.), the second is the IP address, and the third is the bit mask for the IP, assumed to be 255.255.255.255.

-i file, --idfile file

Store POP3 UIDs in file instead of the default .fetchids file.

--invisible

Supress Received header and and spoof the MTA so it looks like mail comes directly from the mailserver host.

-K, --nokeep

Delete all retrieved messages from the mail server.

-k, --keep

Keep copies of all retrieved messages on the mail server.

-L file, --logfile file

Redirect status messages to the specified file. This option is primarily for use in debugging. See the --syslog option.

-l size, --limit size

Set the maximum message size that will be retrieved from a server. Messages larger than this size will be left on the server and marked unread.

-lmtp

Deliver fetched mail via LMTP instead of SMTP. The server, specified with the -S option, must explicitly include the port to be used.

-M interface, --monitor interface

In daemon mode, monitor the specified TCP/IP interface for any activity besides itself, and skip the poll if there is no other activity. Useful for PPP connections that automatically time out with no activity.

-m command, --mda command

Pass mail directly to mail delivery agent instead of sending to port 25. The command is the path and options for the mailer, such as /usr/lib/sendmail -oem. A %T in the command will be replaced with the local delivery address, and an %F will be replaced with the message's From address.

-N, --nodetach

Run command in the foreground. Useful for debugging a configuration file that normally would run fetchmail as a daemon. Also causes fetchmail to ignore -L or --syslog options.

-n, --norewrite

Do not expand local mail IDs to full addresses. This option will disable expected addressing and should be used only to find problems.

--nobounce

Do not bounce error messages back to the sender; send them to the postmaster instead.

--nosyslog

Turn off logging to syslogd. This option overrides resource file settings and the -L option.

-P n, --port n

Specify a port to connect to on the mail server. The default port numbers for supported protocols are usually sufficient.

-p proto, --protocol proto

Specify the protocol to use when polling a mail server. proto can be:

AUTO: Attempt IMAP, POP3, then POP2.
POP2: Post Office Protocol 2.
POP3: Post Office Protocol 3.
APOP: POP3 with MD5 authentication.
KPOP: POP3 with Kerberos v4 authentication on port 1109.
RPOP: POP3 with RPOP authentication.
SDPS: Demon Internet's Standard Dial-up POP3 Service.
IMAP: IMAP2bis, IMAP4, or IMAP4rev1. fetchmail autodetects their capabilities.
ETRN: Extended SMTP with Extended TURN command.
ODMR: On Demand Mail Relaying.

--plugin command

Use external program to establish the TCP connection. The command is the path and options for the external program. Use escape codes %h and %p in command to pass the hostname and port as arguments to the external program. When using this command, fetchmail will write to the program's standard input and read from its standard output.

--plugout command

Same as the --plugin option, but used to establish SMTP connections.

--plugout principal

Authenticate using the specified service principal. Used with POP3 or IMAP with Kerberos authentication.

--postmaster name

If unable to deliver mail, deliver it to name. Set name to "" to have undeliverable mail discarded.

-Q string, --qvirtual string

Remove the prefix string, which is the local user's hostid, from the address in the envelope header (such as "Delivered-To:").

-q, --quit

Kill a running daemon process before performing any other commands.

-r folder, --folder folder

Retrieve the specified mail folder from the mail server.

-S hostlist, -smtphost hostlist

Attempt to forward mail to one of the SMTP hosts listed in the comma-separated hostlist. The hosts are tried in the order they are given. The host may be a domain name, IP address, or the directory path to an LMTP socket. Port numbers can be appended to domain names and IP addresses using /port notation.

-s, --silent

Suppress status messages during a fetch.

--showdots

Always print progress dots. By default fetchmail prints progress dots only when the current tty is standard output.

--smtpname user

Specify the user and domain name to use in RCPT TO lines sent to SMTP. user should be in the form user@domain. By default, fetchmail uses the local user and domain.

-syslog

Redirect status and error messages to the syslog daemon.

--ssl

Encrypt connection to mail server using Secure Socket Layer.

--sslcert file

Specify the file containing the client-side public SSL certificate.

--sslkey file

Specify the file containing the client-side private SSL key.

--sslproto proto

Specify a specific SSL protocol to use. proto may be ssl2, ssl3, or tls1.

--sslcertck

Fail unless the server's certificate has been signed by a local list of trusted certificates. proto may be ssl2, ssl3, or tls1.

--sslcertpath directory

Specify the directory containing trusted certificates to be used with --sslcertck.

--sslfingerprint hash

Fail unless the server's key fingerprint matches the specified fingerprint hash. hash is an MD5 hash of the server's key given in hexadecimal notation, using colons to separate groups of two digits. Letter hex digits must be in uppercase.

-t n, --timeout n

Set the non-response timeout to n seconds.

--tracepolls

Add information about the account and server being polled to the Received header of each message received.

-U, --uidl

For POP3, track the age of kept messages via unique ID listing.

-u name, --username name

Specify the user name to use when logging into the mail server.

-V, --version

Print the version information for fetchmail and display the options set for each mail server. Perform no fetch.

-v, --verbose

Display all status messages during a fetch.

-w n, --warnings n

When issuing warnings about oversized messages, wait n seconds after each warning before sending another warning.

-Z nnn, --antispam nnn

Specify the SMTP error nnn to signal a spam block from the client. If nnn is -1, this option is disabled. Multiple SMTP codes may be given as a comma-separated list. By default fetchmail discards messages with error codes 571, 550, 501, and 554.

fgconsole

fgconsole

Print the number of the current virtual console. For example, if you are using /dev/tty1, the command would return 1.

fgrep

fgrep [options] pattern [files]

Search one or more files for lines that match a literal text string pattern. Exit status is 0 if any lines match, 1 if not, and 2 for errors.

See grep for the list of available options. Also see egrep.

Examples

Print lines in file that don't contain any spaces:

fgrep -v ' ' file

Print lines in file that contain the words in the file spell_list:

fgrep -f spell_list file

file

file [options] files

Classify the named files according to the type of data they contain. file checks the magic file (usually /usr/share/magic) to identify some file types.

Options

-b: Brief mode; do not prepend filenames to output lines.
-c: Check the format of the magic file (files argument is invalid with -c). Usually used with -m.
-f file: Read the names of files to be checked from file.
-L: Follow symbolic links. By default, symbolic links are not followed.
-m file: Search for file types in file instead of /usr/share/magic.
-n: Flush standard output after checking a file.
-s: Check files that are block or character special files in addition to checking ordinary files.
-v: Print the version.
-z: Attempt checking of compressed files.

Many file types are understood. Output lists each filename, followed by a brief classification such as:

ascii text
c program text
c-shell commands
data
empty
iAPX 386 executable
directory
[nt]roff, tbl, or eqn input text
shell commands
symbolic link to ../usr/etc/arp

Example

List all files that are deemed to be troff/nroff input:

file * | grep roff

find

find [pathnames] [conditions]

An extremely useful command for finding particular groups of files (numerous examples follow this description). find descends the directory tree beginning at each pathname and locates files that meet the specified conditions. The default pathname is the current directory. The most useful conditions include -print (which is the default if no other expression is given), -name and -type (for general use), -exec and -size (for advanced use), and -mtime and -user (for administrators).

Conditions may be grouped by enclosing them in  (escaped parentheses), negated with ! (use \! in tcsh), given as alternatives by separating them with -o, or repeated (adding restrictions to the match; usually only for -name, -type, or -perm). Note that "modification" refers to editing of a file's contents, whereas "change" means a modification, or permission or ownership changes. In other words, -ctime is more inclusive than -atime or -mtime.

Conditions and actions

-atime +n | -n | n: Find files that were last accessed more than n (+n), less than n (-n), or exactly n days ago. Note that find changes the access time of directories supplied as pathnames.
-ctime +n | -n | n: Find files that were changed more than n (+n), less than n (-n), or exactly n days ago. A change is anything that changes the directory entry for the file, such as a chmod.
-depth: Descend the directory tree, skipping directories and working on actual files first, and then the parent directories. Useful when files reside in unwritable directories (e.g., when using find with cpio).
-exec command { } \;: Run the Linux command, from the starting directory on each file matched by find (provided command executes successfully on that file, i.e., returns a 0 exit status). When command runs, the argument { } substitutes the current file. Follow the entire sequence with an escaped semicolon (\;). In some shells, the braces may need to be escaped as well.
-follow: Follow symbolic links and track the directories visited (don't use with -type l).
-group gname: Find files belonging to group gname. gname can be a group name or a group ID number.
-inum n: Find files whose inode number is n.
-links n: Find files having n links.
-mount, -xdev: Search only for files that reside on the same filesystem as pathname.
-mtime +n | -n | n: Find files that were last modified more than n (+n), less than n (-n), or exactly n days ago. A modification is a change to a file's data.
-name pattern: Find files whose names match pattern. Filename metacharacters may be used but should be escaped or quoted.
-newer file: Find files that were modified more recently than file; similar to -mtime. Affected by -follow only if it occurs after -follow on the command line.
-ok command { }\;: Same as -exec, but prompts user to respond with y before command is executed.
-perm nnn: Find files whose permission flags (e.g., rwx) match octal number nnn exactly (e.g., 664 matches -rw-rw-r--). Use a minus sign before nnn to make a "wildcard" match of any unspecified octal digit (e.g., -perm -600 matches -rw-******, where * can be any mode).
-print: Print the matching files and directories, using their full pathnames. Return true.
-regex pattern: Like -path, but uses grep-style regular expressions instead of the shell-like globbing used in -name and -path.
-size n[c]: Find files containing n blocks, or if c is specified, n characters long.
-type c: Find files whose type is c. c can be b (block special file), c (character special file), d (directory), p (fifo or named pipe), l (symbolic link), s (socket), or f (plain file).
-user user: Find files belonging to user (name or ID).
-daystart: Calculate times from the start of the day today, not 24 hours ago.
-maxdepth num: Do not descend more than num levels of directories.
-mindepth num: Begin applying tests and actions only at levels deeper than num levels.
-noleaf: Normally, find assumes that each directory has at least two hard links that should be ignored (a hard link for its name and one for "."; i.e., two fewer "real" directories than its hard link count indicates). -noleaf turns off this assumption, a useful practice when find runs on non-Unix-style filesystems. This forces find to examine all entries, assuming that some might prove to be directories into which it must descend (a time-waster on Unix).
-amin +n | -n | n: Find files last accessed more than n (+n), less than n (-n), or exactly n minutes ago.
-anewer file: Find files that were accessed after file was last modified. Affected by -follow when after -follow on the command line.
-cmin +n | -n | n: Find files last changed more than n (+n), less than n (-n), or exactly n minutes ago.
-cnewer file: Find files that were changed after they were last modified. Affected by -follow when after -follow on the command line.
-empty: Continue if file is empty. Applies to regular files and directories.
-false: Return false value for each file encountered.
-fstype type: Match files only on type filesystems. Acceptable types include minix, ext, ext2, xia, msdos, umsdos, vfat, proc, nfs, iso9660, hpfs, sysv, smb, and ncpfs.
-gid num: Find files with numeric group ID of num.
-ilname pattern: A case-insensitive version of -lname.
-iname pattern: A case-insensitive version of -name.
-ipath pattern: A case-insensitive version of -path.
-iregex pattern: A case-insensitive version of -regex.
-lname pattern: Search for files that are symbolic links, pointing to files named pattern. pattern can include shell metacharacters and does not treat / or . specially. The match is case-insensitive.
-mmin +n | -n | n: Find files last modified more than n (+n), less than n (-n), or exactly n minutes ago.
-nouser: The file's user ID does not correspond to any user.
-nogroup: The file's group ID does not correspond to any group.
-path pattern: Find files whose names match pattern. Expect full pathnames relative to the starting pathname (i.e., do not treat / or . specially).

Examples

List all files (and subdirectories) in your home directory:

find $HOME -print

List all files named chapter1 in the /work directory:

find /work -name chapter1

List all files beginning with memo owned by ann:

find /work -name 'memo*' -user ann -print

Search the filesystem (begin at root) for manpage directories:

find / -type d -name 'man*' -print

Search the current directory, look for filenames that don't begin with a capital letter, and send them to the printer:

find . \! -name '[A-Z]*' -exec lpr {  }\;

Find and compress files whose names don't end with .gz:

gzip `find . \! -name '*.gz' -print`

Remove all empty files on the system (prompting first):

find / -size 0 -ok rm {  } \;

Search the system for files that were modified within the last two days (good candidates for backing up):

find / -mtime -2 -print

Recursively grep for a pattern down a directory tree:

find /book -print | xargs grep '[Nn]utshell'

If the files kt1 and kt2 exist in the current directory, their names can be printed with the command:

$ find . -name 'kt[0-9]'
./kt1
./kt2

Since the command prints these names with an initial ./ path, you need to specify the ./ when using the -path option:

$ find . -path './kt[0-9]'
./kt1
./kt2

The -regex option uses a complete pathname, like -path, but treats the following argument as a regular expression rather than a glob pattern (although in this case the result is the same):

$ find . -regex './kt[0-9]'
./kt1
./kt2

finger

finger [options] users

Display data about one or more users, including information listed in the files .plan and .project in each user's home directory. You can specify each user either as a login name (exact match) or as a first or last name (display information on all matching names). Networked environments recognize arguments of the form user@host and @host.

Options

-l: Force long format (default): everything included by the -s option and home directory, home phone, login shell, mail status, .plan, .project, and .forward.
-m: Suppress matching of users' "real" names.
-p: Omit .plan and .project files from display.
-s: Show short format: login name, real name, terminal name, write status, idle time, office location, and office phone number.

fingerd

in.fingerd [options]

TCP/IP command. Remote user information server. fingerd provides a network interface to the finger program. It listens for TCP connections on the finger port and, for each connection, reads a single input line, passes the line to finger, and copies the output of finger to the user on the client machine. fingerd is started by inetd and must have an entry in inetd's configuration file, /etc/inetd.conf.

Options

-f: Allow finger forwarding in the form of user@host1@host2.
-p command, -L path: Use alternate finger program specified by command.
-l: Log finger requests.
-t n: Set timeout period to n seconds.
-u: Reject requests in the form of @host.
-w: Include additional information, such as uptime and the name of the operating system.

flex

flex [options] [file]

flex (Fast Lexical Analyzer Generator) is a faster variant of lex. It generates a lexical analysis program (named lex.yy.c) based on the regular expressions and C statements contained in one or more input files. See also bison, yacc, and the O'Reilly book lex & yacc.

Options

-b: Generate backup information to lex.backup.
-d: Debug mode.
-f: Use faster compilation (limited to small programs).
-h: Help summary.
-i: Scan case-insensitively.
-l: Maximum lex compatibility.
-o file: Write output to file instead of lex.yy.c.
-p: Print performance report.
-s: Exit if the scanner encounters input that does not match any of its rules.
-t: Print to standard output. (By default, flex prints to lex.yy.c.)
-v: Print a summary of statistics.
-w: Suppress warning messages.
-B: Generate batch (noninteractive) scanner.
-F: Use the fast scanner table representation.
-I: Generate an interactive scanner (default).
-L: Suppress #line directives in lex.yy.c.
-P prefix: Change default yy prefix to prefix for all globally visible variable and function names.
-V: Print version number.
-7: Generate a 7-bit scanner.
-8: Generate an 8-bit scanner (default).
-+: Generate a C++ scanner class.
-C: Compress scanner tables but do not use equivalence classes.
-Ca: Align tables for memory access and computation. This creates larger tables but gives faster performance.
-Ce: Construct equivalence classes. This creates smaller tables and sacrifices little performance (default).
-Cf: Generate full scanner tables, not compressed.
-CF: Generate faster scanner tables, like -F.
-Cm: Construct metaequivalence classes (default).
-Cr: Bypass use of the standard I/O library; use read( ) system calls instead.

fmt

fmt [options] [files]

Convert text to specified width by filling lines and removing newlines. Concatenate files on the command line, or read text from standard input if - (or no file) is specified. By default, preserve blank lines, spacing, and indentation. fmt attempts to break lines at the end of sentences and avoid breaking lines after a sentence's first word or before its last.

Options

-c, --crown-margin: Crown margin mode. Do not change indentation of each paragraph's first two lines. Use the second line's indentation as the default for subsequent lines.
-p prefix, --prefix=prefix: Format only lines beginning with prefix.
-s, --split-only: Suppress line-joining.
-t, --tagged-paragraph: Tagged paragraph mode. Same as crown mode when the indentations of the first and second lines differ. If the indentation is the same, treat the first line as its own separate paragraph.
-u, --uniform-spacing: Reduce spacing to a maximum of one space between words and two between sentences.
-w width, --width=width: Set output width to width. The default is 75.
--help: Print help message and then exit.
--version: Print version information and then exit.

fold

fold [option] [files]

Break the lines of the named files so that they are no wider than the specified width (default is 80). fold breaks lines exactly at the specified width, even in the middle of a word. Reads from standard input when given - as a file.

Options

-b, --bytes: Count bytes, not columns (i.e., consider tabs, backspaces, and carriage returns to be one column).
-s, --spaces: Break at spaces only, if possible.
-w, --width width, -width: Set the maximum line width to width. The flags -w 6, --width 6, and -6 will all set the maximum width to six columns.

formail

formail [options]

Filter standard input into mailbox format. Useful for splitting mail digests or passing the contents of a mail file to another program such as a spam filter for additional processing. If no sender is apparent, provide the sender foo@bar. By default, escape bogus From lines with >.

Options

+skip: Do not split first skip messages.
-total: Stop after splitting total messages.
-a headerfield: Append headerfield to header, unless it already exists. If headerfield is Message-ID or Resent-Message-ID with no contents, generate a unique message ID.
-b: Do not escape bogus From lines.
-c: When header fields are more than one line long, concatenate the lines.
-d: Do not assume that input must be in strict mailbox format. This option disables recognition of the Content-Length field so you can split digests or use nonstandard mailbox formats
-e: Allow messages to begin one immediately after the other; do not require empty space between them.
-f: Do not edit non-mailbox-format lines. By default, formail prepends From to such lines.
-i headerfield: Append headerfield whether or not it already exists. Rename each existing headerfield to Old-headerfield, unless it is empty.
-k: For use only with -r. Keep the body as well as the fields specified by -r.
-m minfields: Require at least minfields before recognizing the beginning of a new message. Default is 2.
-n: Allow simultaneous formail processes to run.
-p prefix: Escape lines with prefix instead of >.
-q: Do not display write errors, duplicate messages, and mismatched Content-Length fields. This is the default; use -q- to turn it off.
-r: Throw away all existing fields, retaining only X-Loop, and generate autoreply header instead. You can preserve particular fields with the -i option.
-s: Must be the last option; everything following it will be assumed to be its arguments. Divide input to separate mail messages, and pipe them to the program specified or concatenate them to standard output (by default).
-t: Assume sender's return address to be valid. (By default, formail favors machine-generated addresses.)
-u headerfield: Delete all but the first occurrence of headerfield.
-x headerfield: Display the contents of headerfield on a single line.
-z: When necessary, add a space between field names and contents. Remove ("zap") empty fields.
-A headerfield: Append headerfield whether or not it already exists.
-B: Assume that input is in BABYL rmail format.
-D maxlen idcache: Remember old message IDs (in idcache, which will grow no larger than approximately maxlen). When splitting, refuse to output duplicate messages. Otherwise, return true on discovering a duplicate. With -r, look at the sender's mail address instead of the message ID.
-I headerfield: Append headerfield whether or not it already exists. Remove existing fields.
-R oldfield newfield: Change all fields named oldfield to newfield.
-U headerfield: Delete all but the last occurrence of headerfield.
-Y: Format in traditional Berkeley style (i.e., ignore Content-Length fields).
-X headerfield

free

free [options]

Display statistics about memory usage: total free, used, physical, swap, shared, and buffers used by the kernel.

Options

-b: Calculate memory in bytes.
-k: Default. Calculate memory in kilobytes.
-m: Calculate memory in megabytes.
-o: Do not display "buffer adjusted" line. The -o switch disables the display "-/+ buffers" line that shows buffer memory subtracted from the amount of memory used and added to the amount of free memory.
-s time: Check memory usage every time seconds.
-t: Display all totals on one line at the bottom of output.
-V: Display version information.

fsck

fsck [options] [filesystem] ...

System administration command. Call the filesystem checker for the appropriate system type to check and repair unmounted filesystems. If a filesystem is consistent, the number of files, number of blocks used, and number of blocks free are reported. If a filesystem is inconsistent, fsck prompts before each correction is attempted. fsck's exit code can be interpreted as the sum of all conditions that apply:

1: Errors were found and corrected.
2: Reboot suggested.
4: Errors were found but not corrected.
8: fsck encountered an operational error.
16: fsck was called incorrectly.
128: A shared library error was detected.

Options

--: Pass all subsequent options to filesystem-specific checker. All options that fsck doesn't recognize will also be passed.
-s: Serial mode. Check one filesystem at a time.
-t fstype: Specify the filesystem type. Do not check filesystems of any other type.
-A: Check all filesystems listed in /etc/fstab. The root filesystem is checked first.
-C: Display completion (progress) bar.
-N: Suppress normal execution; just display what would be done.
-P: Meaningful only with -A: check root filesystem in parallel with other systems. This option is potentially dangerous.
-R: Meaningful only with -A: check all filesystems listed in /etc/fstab except the root filesystem.
-T: Suppress printing of title.
-V: Verbose mode.

fsck.minix

fsck.minix [options] device

System administration command. Similar to fsck, but specifically intended for Linux MINIX filesystems.

Options

-a: Automatic mode; repair without prompting.
-f: Force checking, even if kernel has already marked the filesystem. fsck.minix will normally exit without checking if the system appears to be clean.
-l: List filesystems.
-m: Enable MINIX-like "mode not cleared" warnings.
-r: Interactive mode; prompt before making any repairs.
-s: Display information about superblocks.
-v: Verbose mode.

ftp

ftp [options] [hostname]

Transfer files to and from remote network site hostname. ftp prompts the user for a command. The commands are listed after the options. Some of the commands are toggles, meaning they turn on a feature when it is off and vice versa. Note that versions may have different options.

Options

-d: Enable debugging.
-g: Disable filename globbing.
-i: Turn off interactive prompting.
-n: No autologin upon initial connection.
-v: Verbose. Show all responses from remote server.

Commands

![command [args]]: Invoke an interactive shell on the local machine. If arguments are given, the first is taken as a command to execute directly, with the rest of the arguments as that command's arguments.
$macro-name [args]: Execute the macro macro-name that was defined with the macdef command. Arguments are passed to the macro unglobbed.
account [passwd]: Supply a supplemental password that will be required by a remote system for access to resources once a login has been successfully completed. If no argument is given, the user will be prompted for an account password in a non-echoing mode.
append local-file [remote-file]: Append a local file to a file on the remote machine. If remote-file is not given, the local filename is used after being altered by any ntrans or nmap setting. File transfer uses the current settings for type, format, mode, and structure.
ascii: Set the file transfer type to network ASCII (default).
bell: Sound a bell after each file transfer command is completed.
binary: Set file transfer type to support binary image transfer.
bye: Terminate FTP session and then exit ftp.
case: Toggle remote computer filename case mapping during mget. The default is off. When case is on, files on the remote machine with all-uppercase names will be copied to the local machine with all-lowercase names.
cd remote-directory: Change working directory on remote machine to remote-directory.
cdup: Change working directory of remote machine to its parent directory.
chmod [mode] [remote-file]: Change file permissions of remote-file. If options are omitted, the command prompts for them.
close: Terminate FTP session and return to command interpreter.
cr: Toggle carriage return stripping during ASCII-type file retrieval.
delete remote-file: Delete file remote-file on remote machine.
debug [debug-value]: Toggle debugging mode. If debug-value is specified, it is used to set the debugging level.
dir [remote-directory] [local-file]: Print a listing of the contents in the directory remote-directory and, optionally, place the output in local-file. If no directory is specified, the current working directory on the remote machine is used. If no local file is specified or - is given instead of the filename, output comes to the terminal.
disconnect: Synonym for close.
form format: Set the file transfer form to format. Default format is file.
get remote-file [local-file]: Retrieve the remote-file and store it on the local machine. If the local filename is not specified, it is given the same name it has on the remote machine, subject to alteration by the current case, ntrans, and nmap settings. If local file is -, output comes to the terminal.
glob: Toggle filename expansion for mdelete, mget, and mput. If globbing is turned off, the filename arguments are taken literally and not expanded.
hash: Toggle hash sign (#) printing for each data block transferred.
help [command]: Print help information for command. With no argument, ftp prints a list of commands.
idle [seconds]: Get/set idle timer on remote machine. seconds specifies the length of the idle timer; if omitted, the current idle timer is displayed.
image: Same as binary.
lcd [directory]: Change working directory on local machine. If directory is not specified, the user's home directory is used.
ls [remote-directory] [local-file]: Print listing of contents of directory on remote machine, in a format chosen by the remote machine. If remote-directory is not specified, current working directory is used.
macdef macro-name: Define a macro. Subsequent lines are stored as the macro macro-name; a null line terminates macro input mode. When $i is included in the macro, loop through arguments, substituting the current argument for $i on each pass. Escape $ with \.
mdelete remote-files: Delete the remote-files on the remote machine.
mdir remote-files local-file: Like dir, except multiple remote files may be specified.
mget remote-files: Expand the wildcard expression remote-files on the remote machine and do a get for each filename thus produced.
mkdir directory-name: Make a directory on the remote machine.
mls remote-files local-file: Like nlist, except multiple remote files may be specified, and the local file must be specified.
mode [mode-name]: Set file transfer mode to mode-name. Default mode is stream mode.
modtime [file-name]: Show last modification time of the file on the remote machine.
mput [local-files]: Expand wildcards in local-files given as arguments and do a put for each file in the resulting list.
newer remote-file [local-file]: Get file if remote file is newer than local file.
nlist [remote-directory] [local-file]: Print list of files in a directory on the remote machine to local-file (or to the screen if local-file is not specified). If remote-directory is unspecified, the current working directory is used.
nmap [inpattern outpattern]: Set or unset the filename mapping mechanism. The mapping follows the pattern set by inpattern, a template for incoming filenames, and outpattern, which determines the resulting mapped filename. The sequences $1 through $9 are treated as variables; for example, the inpattern $1.$2, along with the input file readme.txt, would set $1 to readme and $2 to txt. An outpattern of $1.data would result in an output file of readme.data. $0 corresponds to the complete filename. [string1, string2] is replaced by string1 unless that string is null, in which case it's replaced by string2.
ntrans [inchars [outchars ]]: Set or unset the filename character translation mechanism. Characters in a filename matching a character in inchars are replaced with the corresponding character in outchars. If no arguments are specified, the filename mapping mechanism is unset. If arguments are specified:

Characters in remote filenames are translated during mput and put commands issued without a specified remote target filename.

Characters in local filenames are translated during mget and get commands issued without a specified local target filename.
open host [port]: Establish a connection to the specified host FTP server. An optional port number may be supplied, in which case ftp will attempt to contact an FTP server at that port.
prompt: Toggle interactive prompting.
proxy ftp-command: Execute an FTP command on a secondary control connection (i.e., send commands to two separate remote hosts simultaneously).
put local-file [remote-file]: Store a local file on the remote machine. If remote-file is left unspecified, the local filename is used after processing according to any ntrans or nmap settings in naming the remote file. File transfer uses the current settings for type, file, structure, and transfer mode.
pwd: Print name of the current working directory on the remote machine.
quit: Synonym for bye.
quote arg1 arg2...: Send the arguments specified, verbatim, to the remote FTP server.
recv remote-file [local-file]: Synonym for get.
reget remote-file [local-file]: Retrieve a file (like get), but restart at the end of local-file. Useful for restarting a dropped transfer.
remotehelp [command-name]: Request help from the remote FTP server. If command-name is specified, remote help for that command is returned.
remotestatus [filename]: Show status of the remote machine or, if filename is specified, of filename on remote machine.
rename [from] [to]: Rename file from on remote machine to to.
reset: Clear reply queue.
restart marker: Restart the transfer of a file from a particular byte count.
rmdir [directory-name]: Delete a directory on the remote machine.
runique: Toggle storing of files on the local system with unique filenames. When this option is on, rename files as .1 or .2, and so on, as appropriate, to preserve unique filenames, and report each such action. Default value is off.
send local-file [remote-file]: Synonym for put.
sendport: Toggle the use of PORT commands.
site [command]: Get/set site-specific information from/on remote machine.
size filename: Return size of filename on remote machine.
status: Show current status of ftp.
struct [struct-name]: Set the file transfer structure to struct-name. By default, stream structure is used.
sunique: Toggle storing of files on remote machine under unique filenames.
system: Show type of operating system running on remote machine.
tenex: Set file transfer type to that needed to talk to TENEX machines.
trace: Toggle packet tracing.
type [type-name]: Set file transfer type to type-name. If no type is specified, the current type is printed. The default type is network ASCII.
umask [mask]: Set user file-creation mode mask on the remote site. If mask is omitted, the current value of the mask is printed.
user username [password] [account]: Identify yourself to the remote FTP server. ftp will prompt the user for the password (if not specified and the server requires it) and the account field.
verbose: Toggle verbose mode.
? [command]: Same as help.

ftpd

in.ftpd [options]

TCP/IP command. Internet File Transfer Protocol server. The server uses the TCP protocol and listens at the port specified in the ftp service specification. ftpd is started by inetd and must have an entry in inetd's configuration file, /etc/inetd.conf. There are several FTP daemons available. On many Linux distributions the default is wu-ftpd, which we document here.

Options

-a: Read access information from configuration file /etc/ftpaccess.
-d, -v: Write debugging information to syslogd.
-i: Log all files received in the transfer log /var/log/xferlog.
-l: Log each FTP session in syslogd.
-o: Log all files sent in the transfer log /var/log/xferlog.
-pport: Use port as the FTP control port instead of reading the appropriate port from /etc/services. Works only in standalone mode.
-q: Use PID files to record the process IDs of running daemons. This is the default. These files are needed to determine the current number of users.
-rdir: Change system root (chroot) to specified directory when loaded.
-s: Run ftpd standalone in the foreground.
-ttimeout: Set default timeout period to timeout seconds.
-uumask: Set default umask to umask.
-w: Record user logins in the wtmp file. This is the default.
-x: Used with options -i and -o. Log file transfers to syslogd as well as the tranfer log.
-z option: Set Transport Security Layer (TSL) option for Secure Socket Layers. See wu-ftpd documentation for more details.
-A: Do not read access information from configuration file /etc/ftpaccess. This is the default.
-I: Do not use ident to determine client's remote username.
-L: Log all commands sent to ftpd in syslogd. This option is overriden by option -a.
-Pport: Use port as the FTP data port instead of reading the appropriate port from /etc/services.
-Q: Do not use PID files to record the process IDs of running daemons. Without PID files, there is no imposed limit to the number of concurrent users.
-S: Run ftpd standalone in the background.
-Tmaxtimeout: Set maximum timeout period in seconds. Default limit is 15 minutes.
-U: Record user logins in the utmp file. By default, logins are not recorded.
-V: Print version, then exit.
-W: Do not record user logins in the wtmp file.
-X

fuser

fuser [options] [files | filesystems]

Identifies and outputs the process IDs of processes that are using the files or local filesystems. Each process ID is followed by a letter code: c if process is using file as the current directory; e if executable; f if an open file; m if a shared library; and r if the root directory. Any user with permission to read /dev/kmem and /dev/mem can use fuser, but only a privileged user can terminate another user's process. fuser does not work on remote (NFS) files.

If more than one group of files is specified, the options may be respecified for each additional group of files. A lone dash (-) cancels the options currently in force, and the new set of options applies to the next group of files. Like a number of other administrator commands, fuser is usually installed to the /sbin directory. You may need to add that directory to your path or execute the command as /sbin/fuser.

Options

-: Return all options to defaults.
-signal: Send signal instead of SIGKILL.
-a: Display information on all specified files, even if they are not being accessed by any processes.
-i: Request user confirmation to kill a process. Ignored if -k is not also specified.
-k: Send SIGKILL signal to each process.
-l: List signal names.
-m: Expect files to exist on a mounted filesystem; include all files accessing that filesystem.
-n space: Set the namespace checked for usage. Acceptable values are file for files, udp for local UPD ports, and tcp for local TCP ports.
-s: Silent.
-u: User login name, in parentheses, also follows process ID.
-v: Verbose.
-V: Display version information.

g++

g++ [options] files

Invoke gcc with the options necessary to make it recognize C++. g++ recognizes all the file extensions gcc does, in addition to C++ source files (.C, .cc, or .cxx files) and C++ preprocessed files (.ii files). See also gcc.

gawk

gawk [options] 'script' [var=value...] [files]
gawk [options] -f scriptfile [var=value...] [files]

The GNU version of awk, a program that does pattern matching, record processing, and other forms of text manipulation. For more information, see Chapter 13.

gcc

gcc [options] files

GNU Compiler Collection. gcc, formerly known as the GNU C Compiler, compiles multiple languages (C, C++, Objective-C, Ada, FORTRAN, and Java) to machine code. Here we document its use to compile C, C++, or Objective-C code. gcc compiles one or more programming source files; for example, C source files (file.c), assembler source files (file.s), or preprocessed C source files (file.i). If the file suffix is not recognizable, assume that the file is an object file or library. gcc normally invokes the C preprocessor, compiles the process code to assemble language code, assembles it, and then links it with the link editor. This process can be stopped at one of these stages using the -c, -S, or -E option. The steps may also differ depending on the language being compiled. By default, output is placed in a.out. In some cases, gcc generates an object file having a .o suffix and a corresponding root name.

Preprocessor and linker options given on the gcc command line are passed on to these tools when they are run. These options are briefly described here, but some are more fully described under entries for cpp, as, and ld. The options that follow are divided into general, preprocessor, linker, and warning options. gcc accepts many system-specific options not covered here.

Note: gcc is the GNU form of cc; on most Linux systems, the command cc will invoke gcc. The command g++ will invoke gcc with the appropriate options for interpreting C++.

General options

-a

Provide profile information for basic blocks.

-aux-info file

Print prototyped declarations and information on their origins to file.

-ansi

Enforce full ANSI conformance.

-b machine

Compile for use on machine type.

-c

Create linkable object file for each source file, but do not call linker.

-dumpmachine

Print compiler's default target machine, then exit.

-dumpspecs

Print built-in specification strings, then exit.

-dumpversion

Set the specified compiler option. Many of these control debugging, optimization of code, and special language options. Use the --help -v options for a full listing.

-foption

-g

Include debugging information for use with gdb.

-glevel

Provide level amount of debugging information. level must be 1, 2, or 3, with 1 providing the least amount of information. The default is 2.

--help

Print most common basic options, then exit. When used with option -v, print options for all of gcc's subprocesses. For options specific to a target, use --target-help.

-moption

Set the specified machine specific option. Use the --target-help option for a full listing.

-o file

Specify output file as file. Default is a.out.

-p

Provide profile information for use with prof.

-pass-exit-codes

On error, return highest error code as the exit code instead of 1.

-pedantic

Warn verbosely.

-pedantic-errors

Generate an error in every case in which -pedantic would have produced a warning.

-pg

Provide profile information for use with gprof.

-print-file-name=file

Print the full path to the library specified by filename file, then exit. This is the library gcc would use for linking.

-print-search-dirs

Print installation directory and the default list of directories gcc will search to find programs and libraries, then exit.

-pipe

Transfer information between stages of compiler by pipes instead of temporary files.

-save-temps

Save temporary files in the current directory when compiling.

-std=standard

Specify C standard of input file. Accepted values are:

iso9899:1990, c89: 1990 ISO C standard.
iso9899:199409: 1994 amendment to the 1990 ISO C standard.
iso9899:1999, c99, iso9899:199x, c9x: 1999 revised ISO C standard.
gnu89: 1990 C Standard with GNU extensions (the default value).
gnu99, gnu9x: 1999 revised ISO C standard with GNU extensions.

-time

Print statistics on the execution of each subprocess.

-v

Verbose mode. Print subprocess commands to standard error as they are executed. Include gcc version number and preprocessor version number. To generate the same output without executing commands, use the option -###.

-w

Suppress warnings.

-x language

Expect input file to be written in language, which may be c, objective-c, c-header, c++, ada, f77, ratfor, assembler, java, cpp-output, c++-cpp-output, objc-cpp-output, f77-cpp-output, assembler-with-cpp, or ada. If none is specified as language, guess the language by filename extension.

-Bpath

Specify the path directory in which the compiler files are located.

-E

Preprocess the source files, but do not compile. Print result to standard output. This option is useful to meaningfully pass some cpp options that would otherwise break gcc, such as -C, -M, or -P.

-Idir

Include dir in list of directories to search for include files. If dir is -, search those directories specified by -I before the -I- only when #include "file" is specified, not #include <file>.

-Ldir

Search dir in addition to standard directories.

-O[level]

Optimize. level should be 1, 2, 3, or 0 (the default is 1). 0 turns off optimization; 3 optimizes the most.

-S

Compile source files into assembler code, but do not assemble.

-V version

Attempt to run gcc version version.

-Wa,options

Pass options to the assembler. Multiple options are separated by commas.

-Wl,options

Pass options to the linker. Multiple options are separated by commas.

-Wp,options

Pass options to the preprocessor. Multiple options are separated by commas.

-Xlinker options

Pass options to the linker. A linker option with an argument requires two -Xlinkers, the first specifying the option and the second specifying the argument. Similar to -Wl.

Preprocessor options

gcc will pass the following options to the preprocessor:

-$: Do not allow $ in identifiers.
-dD, -dI, -dM, -dN: Suppress normal output; print preprocessor instructions instead. See cpp for details.
-idirafter dir: Search dir for header files when a header file is not found in any of the included directories.
-imacros file: Process macros in file before processing main files.
-include file: Process file before main file.
-iprefix prefix: When adding directories with -iwithprefix, prepend prefix to the directory's name.
-isystem dir: Search dir for header files after searching directories specified with -I but before searching standard system directories.
-iwithprefix dir: Append dir to the list of directories to be searched when a header file cannot be found in the main include path. If -iprefix has been set, prepend that prefix to the directory's name.
-iwithprefixbefore dir: Insert dir at the beginning of the list of directories to be searched when a header file cannot be found in the main include path. If -iprefix has been set, prepend that prefix to the directory's name.
-nostdinc: Search only specified, not standard, directories for header files.
-nostdinc++: Suppress searching of directories believed to contain C++-specific header files.
-trigraphs: Convert special three-letter sequences, meant to represent missing characters on some terminals, into the single character they represent.
-undef: Suppress definition of all nonstandard macros.
-A name[=def]: Assert name with value def as if defined by #assert. To turn off standard assertions, use -A-.
-A -name[=def]: Cancel assertion name with value def.
-C: Retain all comments except those found on cpp directive lines. By default, the preprocessor strips C-style comments.
-Dname[=def]: Define name with value def as if by #define. If no =def is given, name is defined with value 1. -D has lower precedence than -U.
-H: Print pathnames of included files, one per line, on standard error.
-M, -MG, -MF, -MD, -MMD, -MQ, -MT: Suppress normal output and print Makefile rules describing file dependencies. Print a rule for make that describes the main source file's dependencies. If -MG is specified, assume that missing header files are actually generated files, and look for them in the source file's directory. Most of these options imply -E. See cpp for further details.
-Uname

Linker options

gcc will pass the following options to the linker:

-llib: Link to lib.
-nostartfiles: Force linker to ignore standard system startup files.
-nostdlib: Suppress linking to standard library files.
-s: Remove all symbol table and relocation information from the executable.
-shared: Create a shareable object.
-shared-libgcc: Link to a shared version of libgcc if available.
-static: Suppress linking to shared libraries.
-static-libgcc: Link to a static version of libgcc if available.
-u symbol: Force the linker to search libraries for a definition of symbol, and to link to the libraries found.

Warning options

-pedantic: Warn verbosely.
-pedantic-errors: Produce a fatal error in every case in which -pedantic would have produced a warning.
-w: Don't print warnings.
-W: Warn more verbosely than normal.
-Waggregate-return: Warn if any functions that return structures or unions are defined or called.
-Wall: Enable -W, -Wchar-subscripts, -Wcomment, -Wformat, -Wimplicit, -Wmain, -Wmissing-braces, -Wparentheses, -Wreturn-type, -Wsequence-point, -Wswitch, -Wtemplate-debugging, -Wtrigraphs, -Wuninitialized, -Wunknown-pragmas, and -Wunused.
-Wcast-align: Warn when encountering instances in which pointers are cast to types that increase the required alignment of the target from its original definition.
-Wcast-qual: Warn when encountering instances in which pointers are cast to types that lack the type qualifier with which the pointer was originally defined.
-Wchar-subscripts: Warn when encountering arrays with subscripts of type char.
-Wcomment: Warn when encountering the beginning of a nested comment.
-Wconversion: Warn in particular cases of type conversions.
-Werror: Exit at the first error.
-Wformat: Warn about inappropriately formatted printfs and scanfs.
-Wimplicit: Warn when encountering implicit function or parameter declarations.
-Winline: Warn about illegal inline functions.
-Wmain: Warn about malformed main functions.
-Wmissing-braces: Enable more verbose warnings about omitted braces.
-Wmissing-declarations: Warn if a global function is defined without a previous declaration.
-Wmissing-prototypes: Warn when encountering global function definitions without previous prototype declarations.
-Wnested-externs: Warn if an extern declaration is encountered within a function.
-Wno-import: Don't warn about use of #import.
-Wparentheses: Enable more verbose warnings about omitted parentheses.
-Wpointer-arith: Warn when encountering code that attempts to determine the size of a function or void.
-Wredundant-decls: Warn if anything is declared more than once in the same scope.
-Wreturn-type: Warn about violations of sequence point rules defined in the C standard.
-Wreturn-type: Warn about functions defined without return types or with improper return types.
-Wshadow: Warn when a local variable shadows another local variable.
-Wstrict-prototypes: Insist that argument types be specified in function declarations and definitions.
-Wswitch: Warn about switches that skip the index for one of their enumerated types.
-Wtraditional: Warn when encountering code that produces different results in ANSI C and traditional C.
-Wtrigraphs: Warn when encountering trigraphs.
-Wuninitialized: Warn when encountering uninitialized automatic variables.
-Wundef: Warn when encountering a non-macro identifier in an #if directive.
-Wunknown-pragmas: Warn when encountering a #pragma directive not understood by gcc.
-Wunused: Warn about unused variables, functions, labels, and paramaters.

Pragma directives

#pragma interface [header-file]: Used in header files to force object files to provide definition information via references instead of including it locally in each file. C++-specific.
#pragma implementation [header-file]: Used in main input files to force generation of full output from header-file (or, if it is not specified, from the header file with the same base name as the file containing the pragma directive). This information will be globally visible. Normally the specified header file contains a #pragma interface directive.

gdb

gdb [options] [program [core|pid]]

GDB (GNU DeBugger) allows you to step through the execution of a program in order to find the point at which it breaks. It fully supports C and C++, and provides partial support for FORTRAN, Java, Chill, assembly, and Modula-2. The program to be debugged is normally specified on the command line; you can also specify a core or, if you want to investigate a running program, a process ID.

Options

-b bps: Set line speed of serial device used by GDB to bps.
-batch: Exit after executing all the commands specified in .gdbinit and -x files. Print no startup messages.
-c file, -core=file: Consult file for information provided by a core dump.
-cd=directory: Use directory as gdb's working directory.
-d directory, -directory=directory: Include directory in path that is searched for source files.
-e file, -exec=file: Use file as an executable to be read in conjunction with source code. May be used in conjunction with -s to read the symbol table from the executable.
-f, -fullname: Show full filename and line number for each stack frame.
-h, -help: Print help message, then exit.
-n, -nx: Ignore .gdbinit file.
-q, -quiet: Suppress introductory and copyright messages.
-s file, -symbols=file: Consult file for symbol table. With -e, also uses file as the executable.
-tty=device: Set standard in and standard out to device.
-write: Allow gdb to write into executables and core files.
-x file, -command=file: Read gdb commands from file.

Common commands

These are just some of the more common gdb commands; there are too many to list them all.

bt: Print the current location within the program and a stack trace showing how the current location was reached. (where does the same thing.)
break: Set a breakpoint in the program.
cd: Change the current working directory.
clear: Delete the breakpoint where you just stopped.
commands: List commands to be executed when a breakpoint is hit.
c: Continue execution from a breakpoint.
delete: Delete a breakpoint or a watchpoint; also used in conjunction with other commands.
display: Cause variables or expressions to be displayed when program stops.
down: Move down one stack frame to make another function the current one.
frame: Select a frame for the next continue command.
info: Show a variety of information about the program. For instance, info breakpoints shows all outstanding breakpoints and watchpoints.
jump: Start execution at another point in the source file.
kill: Abort the process running under gdb's control.
list: List the contents of the source file corresponding to the program being executed.
next: Execute the next source line, executing a function in its entirety.
print: Print the value of a variable or expression.
ptype: Show the contents of a datatype, such as a structure or C++ class.
pwd: Show the current working directory.
quit: Exit gdb.
reverse-search: Search backward for a regular expression in the source file.
run: Execute the program.
search: Search for a regular expression in the source file.
set variable: Assign a value to a variable.
signal: Send a signal to the running process.
step: Execute the next source line, stepping into a function if necessary.
undisplay: Reverse the effect of the display command; keep expressions from being displayed.
until: Finish the current loop.
up: Move up one stack frame to make another function the current one.
watch: Set a watchpoint (i.e., a data breakpoint) in the program.
whatis

getkeycodes

getkeycodes

Print the kernel's scancode-to-keycode mapping table.

gpm

gpm [options]

System administration command. Provide a mouse server and cut-and-paste utility for use on the Linux console. gpm acts like a daemon, responding to both mouse events and client input. If no clients are connected to the active console, gpm provides cut-and-paste services.

Options

-2: Force two buttons. If there is a middle button, it is treated as the right button.
-3: Force three buttons. With a three-button mouse, the left button makes a selection, the right button extends the selection, and the middle button pastes it. Using this option with a two-button mouse results in being unable to paste.
-a accel: Set the acceleration for a single motion longer than the delta specified with the -d option.
-A [limit]: Start up with pasting disabled for security. If specified, limit gives the time in seconds during which a selection can be pasted. If too much time has passed, the paste is not allowed.
-b baud: Specify the baud rate.
-B seq: Set a three-digit button sequence, mapping the left, middle, and right buttons to buttons 1, 2, and 3. The default is 123. The sequence 321 is useful if you are left-handed, or 132 for a two-button mouse.
-d delta: Set the delta value for use with -a. When a mouse motion event is longer than the specified delta, use accel as a multiplier. delta must be 2 or greater.
-D: Debugging mode. When set, gpm does not put itself into the background, and it logs messages to standard error instead of syslog.
-g num: For a glidepoint device, specify the button to be emulated by a tap. num must be 1, 2, or 3 and refers to the button number before any remapping is done by the -B option. Applies to mman and ps2 protocol decoding.
-h: Print a help message and exit.
-i interval: Specify the upper time limit, in milliseconds, between mouse clicks for the clicks to be considered a double or triple click.
-k: Kill a running gpm. For use with a bus mouse to kill gpm before running X. See also -R.
-l charset: Specify the inword( ) lookup table, which determines what characters can appear in a word. charset is a list of characters. The list can include only printable characters. Specify a range with -, and use \ to escape the following character or to specify an octal character.
-m filename: Specify the mouse file to open. The default is /dev/mouse.
-M: Enable the use of more than one mouse. Options appearing before -M apply to the first mouse; those appearing after it apply to the second mouse. Forces the use of -R.
-o extra-options: Specify a comma-separated list of additional mouse-specific options. See the gpm info page for a description of the mouse types and the possible options.
-p: Keep the pointer visible while text is being selected. The default is not to show the pointer.
-r num: Specify the responsiveness. A higher number causes the cursor to move faster.
-R name: Act as a repeater and pass any mouse data received while in graphical mode to the fifo /dev/gpmdata in the protocol specified by name (default is msc). In addition to certain of the protocol types available with -t, you can specify raw to repeat the data with no protocol translation.
-s num: Specify the sample rate for the mouse device.
-S [commands]: Enable special-command processing (see the next section). Custom commands can be specified as a colon-separated list to associate commands with the left button, middle button, and right button. If a command is omitted, it defaults to sending a signal to init.
-t type: Specify the mouse protocol type. Use -t help for a list of types; those marked with an asterisk (*) can be used with -R.
-v: Print version information and exit.
-V [increment]: Make gpm more or less verbose by the specified increment. The default verbosity level is 5 and the default increment is 1. A larger value of increment causes more messages to be logged. The increment can be negative, but must be specified with no space (e.g., -V-3).

Special commands

Special commands, activated with the -S option, are associated with each mouse button. You can also use -S to customize the commands. To execute a special command, triple-click the left and right buttons (hold down one of the buttons and triple-click the other). A message appears on the console and the speaker beeps twice. At that point, release the buttons and press the desired button within three seconds to activate the associated special command. The default special commands are:

Left button: Reboot by signalling init.
Middle button: Shut down the system with /sbin/shutdown -h now.
Right button

gprof

gprof [options] [object_file]

Display the profile data for an object file. The file's symbol table is compared with the call graph profile file gmon.out (previously created by compiling with gcc -pg). Many of gprof's options take a symbol specification argument, or symspec, to limit the option to specified files or functions. The symspec may be a filename, a function, or a line number. It can also be given as filename:function or filename:linenumber to specify a function or line number in a specific file. gprof expects filenames to contain a period and functions to not contain a period.

Options

-a, --no-static: Do not display statically declared functions. Since their information might still be relevant, append it to the information about the functions loaded immediately before.
-b, --brief: Do not display information about each field in the profile.
-c, --static-call-graph: Consult the object file's text area to attempt to determine the program's static call graph. Display static-only parents and children with call counts of 0.
--demangle[=style], --no-demangle: Specify whether C++ symbols should be demangled or not. They are demangled by default. If profiling a program built by a different compiler, you may need to specify the mangling style.
--function-ordering: Print suggested function order based on profiling data.
--file-ordering file: Print suggested link line order for .o files based on profiling data. Read function name to object file mappings from file. This file can be created using the nm command.
-i, --file-info: Print summary information on data files, then exit.
-k from to: Remove arcs between the routines from and to.
-m n, --min-count[=n]: Don't print count statistics for symbols executed less than n times.
-n[symspec], --time[=symspec]: Propogate time statistics in call graph analysis.
-p[symspec], --flat-profile[=symspec]: Print profile statistics.
-q[symspec], --graph[=symspec]: Print call graph analysis.
-s, --sum: Summarize profile information in the file gmon.sum.
-v, --version: Print version and exit.
-w n, --width=n: Print function index formatted to width n.
-x, --all-lines: When printing annotated source, annotate every line in a basic block, not just the beginning.
-y, --separate-files: Print annotated-source output to separate files instead of standard output. The annotated source for each source file is printed to filename-ann.
-z, --display-unused-functions: Include zero-usage calls.
-A[symspec], --annotated-source[=symspec]: Print annotated source code.
-C[symspec], --exec-counts[=symspec]: Print statistics on the number of times each function is called. When used with option -l, count basic-block execution.
-F routine: Print only information about routine. Do not include time spent in other routines.
-I dirs, --directory-path=dirs: Set directory path to search for source files. The dirs argument may be given as a colon-separated list of directories.
-J[symspec], --no-annotated-source[=symspec]: Don't print annotated source code.
-L, --print-path: Print the path information when printing filenames.
-N[symspec], --no-time[=symspec]: Don't propogate time statistics in call graph analysis.
-P[symspec], --no-flat-profile[=symspec]: Don't print profile statistics
-Q[symspec], --no-graph[=symspec]: Don't print call graph analysis.
-T, --traditional: Print output in BSD style.
-Z[symspec], --no-exec-counts[=symspec]: Don't print statistics on the number of times each function is called.

grep

grep [options] pattern [files]

Search one or more files for lines that match a regular expression pattern. Regular expressions are described in Chapter 9. Exit status is 0 if any lines match, 1 if none match, and 2 for errors. See also egrep and fgrep.

Options

-a, --text

Don't suppress output lines with binary data; treat as text.

-b, --byte-offset

Print the byte offset within the input file before each line of output.

-c, --count

Print only a count of matched lines. With -v or --revert-match option, count nonmatching lines.

-d action, --directories=action

Define an action for processing directories. Possible actions are:

read: Read directories like ordinary files (default).
skip: Skip directories.
recurse: Recursively read all files under each directory. Same as -r.

-e pattern, --regexp=pattern

Search for pattern. Same as specifying a pattern as an argument, but useful in protecting patterns beginning with -.

-f file, --file=file

Take a list of patterns from file, one per line.

-h, --no-filename

Print matched lines but not filenames (inverse of -l).

-i, --ignore-case

Ignore uppercase and lowercase distinctions.

-l, --files-with-matches

List the names of files with matches but not individual matched lines; scanning per file stops on the first match.

--mmap

Try to use memory mapping (mmap) to read input in order to save time.

-n, --line-number

Print lines and their line numbers.

-q, --quiet, --silent

Suppress normal output in favor of quiet mode; scanning stops on the first match.

-r, --recursive

Recursively read all files under each directory. Same as -d recurse.

-s, --no-messages

Suppress error messages about nonexistent or unreadable files.

-v, --invert-match

Print all lines that don't match pattern.

-w, --word-regexp

Match on whole words only. Words are divided by characters that are not letters, digits, or underscores.

-x, --line-regexp

Print lines only if pattern matches the entire line.

-A num, --after-context=num

Print num lines of text that occur after the matching line.

-B num, --before-context=num

Print num lines of text that occur before the matching line.

-C[num], --context[=num], -num

Print num lines of leading and trailing context. Default context is 2 lines.

-E, -extended-regexp

Act like egrep, recognizing extended regular expressions such as (UN|POS)IX to find UNIX and POSIX.

-F, --fixed-strings

Act like fgrep, recognizing only fixed strings instead of regular expressions. Useful when searching for characters that grep normally recognizes as metacharacters.

-G, --basic-regexp

Expect the regular expressions traditionally recognized by grep (the default).

-H, --with-filename

Display, before each line found, the name of the file containing the line. This is done by default if multiple files are submitted to a single grep command.

-V, --version

Print the version number and then exit.

-Z, --null

When displaying filenames, follow each with a zero byte instead of a colon.

Examples

List the number of users who use tcsh:

grep -c /bin/tcsh /etc/passwd

List header files that have at least one #include directive:

grep -l '^#include' /usr/include/*

List files that don't contain pattern:

grep -c pattern files | grep :0

groff

groff [options] [files]
troff [options] [files]

Frontend to the groff document-formatting system, which normally runs troff along with a postprocessor appropriate for the selected output device. Options without arguments can be grouped after a single dash (-). A filename of - denotes standard input.

Options

-a: Generate an ASCII approximation of the typeset output.
-b: Print a backtrace.
-C: Enable compatibility mode.
-dcs, -dname=s: Define the character c or string name to be the string s.
-e: Preprocess with eqn, the equation formatter.
-E: Don't print any error messages.
-ffam: Use fam as the default font family.
-Fdir: Search dir for subdirectories with DESC and font files before the default /usr/lib/groff/font.
-h: Print a help message.
-i: Read standard input after all files have been processed.
-l: Send the output to a print spooler (as specified by the print command in the device description file).
-Larg: Pass arg to the spooler. Each argument should be passed with a separate -L option.
-mname: Read the macro file tmac.name.
-Mdir: Search directory dir for macro files before the default directory /usr/lib/groff/tmac.
-nnum: Set the first page number to num.
-N: Don't allow newlines with eqn delimiters; equivalent to eqn's -N option.
-olist: Output only pages specified in list, a comma-separated list of page ranges.
-p: Preprocess with pic.
-Parg: Pass arg to the postprocessor. Each argument should be passed with a separate -P option.
-rcn, -name=n: Set the number register c or name to n. c is a single character and n is any troff numeric expression.
-R: Preprocess with refer.
-s: Preprocess with soelim.
-S: Use safer mode (i.e., pass the -S option to pic and use the -msafer macros with troff).
-t: Preprocess with tbl.
-Tdev: Prepare output for device dev; the default is ps.
-v: Make programs run by groff print out their version number.
-V: Print the pipeline on stdout instead of executing it.
-wname: Enable warning name. You can specify multiple -w options. See the troff manpage for a list of warnings.
-Wname: Disable warning name. You can specify multiple -W options. See the troff manpage for a list of warnings.
-z: Suppress troff output (except error messages).
-Z: Do not postprocess troff output. Normally groff automatically runs the appropriate postprocessor.

Devices

ascii: Typewriter-like device.
dvi: T_EX dvi format.
latin1: Typewriter-like devices using the ISO Latin-1 character set.
ps: PostScript.
X75: 75-dpi X11 previewer.
X100: 100-dpi X11 previewer.
lj4: HP LaserJet4-compatible (or other PCL5-compatible) printer.

Environment variables

GROFF_COMMAND_PREFIX: If set to be X, groff will run Xtroff instead of troff.
GROFF_FONT_PATH: Colon-separated list of directories in which to search for the devname directory.
GROFF_TMAC_PATH: Colon-separated list of directories in which to search for the macro files.
GROFF_TMPDIR: If set, temporary files will be created in this directory; otherwise, they will be created in TMPDIR (if set) or /tmp (if TMPDIR is not set).
GROFF_TYPESETTER: Default device.
PATH

groffer

groffer [viewing_options] [man_options] [groff_options] 
[file-spec...]
groffer filespec

Groffer displays manpages and groff documents. It accepts the option flags from both man and groff. The filespec argument can be a filename or a manpage or section specified in the format man:page or man:section. For more information, see groff and man.

groupadd

groupadd [options] group

System administration command. Create new group account group. Options -f and -r are added by RedHat and may not be available on all distributions.

Options

-f: Exit with error if group being added already exists. If a gid requested with -g already exists and the -o option has not been specified, assign a different gid as if -g had not been specified.
-ggid: Assign numerical group ID. (By default, the first available number above 500 is used.) The value must be unique unless the -o option is used.
-o: Accept a nonunique gid with the -g option.
-r: Add a system account. Assign the first available number lower than 499.

groupdel

groupdel group

System administration command. Remove group from system account files. You may still need to find and change permissions on files that belong to the removed group.

groupmod

groupmod [options] group

System administration command. Modify group information for group.

Options

-g gid: Change the numerical value of the group ID. Any files that have the old gid must be changed manually. The new gid must be unique unless the -o option is used.
-n name: Change the group name to name.
-o: Override. Accept a nonunique gid.

groups

groups [options] [users]

Show the groups that each user belongs to (default user is the owner of the current group). Groups are listed in /etc/passwd and /etc/group.

Options

--help: Print help message.
--version: Print version information.

grpck

grpck [option] [files]

System administration command. Remove corrupt or duplicate entries in the /etc/group and /etc/gshadow files. Generate warnings for other errors found. grpck will prompt for a "yes" or "no" before deleting entries. If the user replies "no," the program will exit. If run in a read-only mode, the reply to all prompts is "no." Alternate group and gshadow files can be checked. If other errors are found, the user will be encouraged to run the groupmod command.

Option

-r: Read-only mode.

Exit codes

0: Success.
1: Syntax error.
2: One or more bad group entries found.
3: Could not open group files.
4: Could not lock group files.
5: Could not write group files.

grpconv

grpconv
grpunconv

System administration command. Like pwconv, the grpconv command creates a shadowed group file to keep your encrypted group passwords safe from password-cracking programs. grpconv creates the /etc/gshadow file based on your existing /etc/groups file and replaces your encrypted password entries with x. If you add new entries to the /etc/groups file, you can run grpconv again to transfer the new information to /etc/gshadow. It will ignore entries that already have a password of x and convert those that do not. grpunconv restores the encrypted passwords to your /etc/groups file and removes the /etc/gshadow file.

gs [options] [files]

GhostScript, an interpreter for Adobe Systems' PostScript and PDF (Portable Document Format) languages. Used for document processing. With - in place of files, standard input is used.

Options

-- filename arg1 ...: Take the next argument as a filename, but use all remaining arguments to define ARGUMENTS in userdict (not systemdict) as an array of those strings before running the file.
-gnumber1xnumber2: Specify width and height of device; intended for systems like the X Window System.
-q: Quiet startup.
-rnumber, -rnumber1xnumber2: Specify X and Y resolutions (for the benefit of devices, such as printers, that support multiple X and Y resolutions). If only one number is given, it is used for both X and Y resolutions.
-Dname=token, -dname=token: Define a name in systemdict with the given definition. The token must be exactly one token (as defined by the token operator) and must not contain any whitespace.
-Dname, -dname: Define a name in systemdict with a null value.
-Idirectories: Add the designated list of directories at the head of the search path for library files.
-Sname=string, -sname=string: Define a name in systemdict with a given string as value.

Special names

-dDISKFONTS: Causes individual character outlines to be loaded from the disk the first time they are encountered.
-dNOBIND: Disables the bind operator. Useful only for debugging.
-dNOCACHE: Disables character caching. Useful only for debugging.
-dNODISPLAY: Suppresses the normal initialization of the output device. May be useful when debugging.
-dNOPAUSE: Disables the prompt and pause at the end of each page.
-dNOPLATFONTS: Disables the use of fonts supplied by the underlying platform (e.g., the X Window System).
-dSAFER: Disables the deletefile and renamefile operators and the ability to open files in any mode other than read-only.
-dWRITESYSTEMDICT: Leaves systemdict writable.
-sDEVICE=device: Selects an alternate initial output device.
-sOUTPUTFILE=filename: Selects an alternate output file (or pipe) for the initial output device.

gunzip

gunzip [options] [files]

Uncompress files compressed by gzip. See gzip for a list of options.

gzexe

gzexe [option] [files]

Compress executables. When run, these files automatically uncompress, thus trading time for space. gzexe creates backup files (filename~), which should be removed after testing the original.

Option

-d: Decompress files.

gzip

gzip [options] [files]
gunzip [options] [files]
zcat [options] [files]

Compress specified files (or read from standard input) with Lempel-Ziv coding (LZ77). Rename compressed file to filename.gz; keep ownership modes and access/modification times. Ignore symbolic links. Uncompress with gunzip, which takes all of gzip's options except those specified. zcat is identical to gunzip -c and takes the options -fhLV, described here. Files compressed with the compress command can be decompressed using these commands.

Options

-n, --fast, --best: Regulate the speed of compression using the specified digit n, where -1 or --fast indicates the fastest compression method (less compression) and -9 or --best indicates the slowest compression method (most compression). The default compression level is -6.
-a, --ascii: ASCII text mode: convert end-of-lines using local conventions. This option is supported only on some non-Unix systems.
-c, --stdout, --to-stdout: Print output to standard output, and do not change input files.
-d, --decompress, --uncompress: Same as gunzip.
-f, --force: Force compression. gzip would normally prompt for permission to continue when the file has multiple links, its .gz version already exists, or it is reading compressed data to or from a terminal.
-h, --help: Display a help screen and then exit.
-l, --list: Expects to be given compressed files as arguments. Files may be compressed by any of the following methods: gzip, deflate, compress, lzh, or pack. For each file, list uncompressed and compressed sizes (the latter being always -1 for files compressed by programs other than gzip), compression ratio, and uncompressed name. With -v, also print compression method, the 32-bit CRC of the uncompressed data, and the timestamp. With -N, look inside the file for the uncompressed name and timestamp.
-L, --license: Display the gzip license and quit.
-n, --no-name: When compressing, do not save the original filename and timestamp by default. When decompressing, do not restore the original filename if present, and do not restore the original timestamp if present. This option is the default when decompressing.
-N, --name: Default. Save original name and timestamp. When decompressing, restore original name and timestamp.
-q, --quiet: Print no warnings.
-r, --recursive: When given a directory as an argument, recursively compress or decompress files within it.
-S suffix, --suffix suffix: Append .suffix. Default is gz. A null suffix while decompressing causes gunzip to attempt to decompress all specified files, regardless of suffix.
-t, --test: Test compressed file integrity.
-v, --verbose: Print name and percent size reduction for each file.
-V, --version

halt

halt [options]

System administration command. Insert a note in the file /var/log/wtmp; if the system is in runlevel 0 or 6, stop all processes; otherwise, call shutdown -h.

Options

-d: Suppress writing to /var/log/wtmp.
-f: Call halt even when shutdown -nf would normally be called (i.e., force a call to halt, even when not in runlevel 0 or 6).
-h: Place hard drives in standby mode before halt or power off.
-i: Shut down network interfaces before halt.
-n: No sync before reboot or halt.
-p: Perform power off when halting system.
-n: Suppress normal call to sync.
-w: Suppress normal execution; simply write to /var/log/wtmp.

hdparm

hdparm [options] [device]

Read or set the hard drive parameters. This command can be used to tune hard drive performance; it is mostly used with IDE drives, but can also be used with SCSI drives.

Options

The hdparm command accepts many option flags, including some that can result in filesystem corruption if misused. Flags can be used to set or get a parameter. To get a parameter, just pass the flag without a value. To set a parameter, follow the flag with a space and the appropriate value.

-a [n]: Get or set the number of sectors to read ahead in the disk. The default is 8 sectors (4KB); a larger value is more efficient for large, sequential reads, and a smaller value is better for small, random reads. Many IDE drives include this functionality in the drive itself, so this feature is not always necessary.
-A: Enable or disable the IDE read-ahead feature. Usually on by default.
-b [n]: Get or set the bus state for the drive.
-B: Get the Advanced Power Management (APM) data if the drive supports it.
-c [n]: Get or set 32-bit I/O values for IDE drives. Acceptable values are 0 (32-bit support off), 1 (32-bit support on), and 3 (on, but only with a sync sequence).
-C: Check the power status of the drive. This will tell you unknown, active/idle, standby, or sleeping. Use -S, -y, -Y, and -Z to set the power status.
-d [n]: Get or set the using_dma flag for the drive, which may be 0 or 1.
-D: Enable or disable defect handling features that are controlled by the hard drive itself.
-E n: Set CD-ROM read speed to n times normal audio playback speed. Not normally necessary.
-f: Flush and sync the buffer cache on exit.
-g: Query and display drive size and geometry information, such as number of cylinders, heads, and sectors.
-h: Display a short help message.
-i: Display the drive identification information obtained at boot time. If the drive has changed since boot, this information may not be current.
-I: Display more detailed identification information for the drive.
-k [n]: Get or set the keep_settings_over_reset variable. Valid settings are 0 and 1, and a value of 1 will keep the -dmu options when rebooting (soft reset only).
-K [n]: Get or set the keep_features_over_reset variable. Valid settings are 0 and 1, and a value of 1 will keep settings for the flags -APSWXZ over a soft reset.
-L n: Set the door lock flag for the drive. Used for Syquest, ZIP, and JAZ drives.
-m [n]: Get or set the number of sectors used for multiple sector count reading. A value of 0 disables the feature, and values of 2, 4, 8, 16, and 32 are common. Drives that try to support this feature and fail may suffer corruption and data loss.
-n [n]: Set to 0 or 1 to disable or enable the "ignore write errors" flag. This can cause massive data loss if used incorrectly, and is for development purposes only.
-p n: Tune the IDE interface to use PIO mode n, usually an integer between 0 and 5. Incorrect values can result in massive data loss. Support for the PIO mode setting feature varies between IDE chips, so tuning it is not for the faint of heart.
-P n: Set the internal prefetch sector count. Not all drives support the feature.
-q: Suppress output for the flag after this one, unless it is the -i, -v, -t, or -T flag.
-r [n]: Get or set the flag for read-only on the device. A value of 1 marks the device as read-only.
-R: This option should be used by experts only. It registers an IDE interface. See the -U option for further details.
-S n: Set the amount of time a disk is inactive before it spins down and goes into standby mode. Settings from 1 to 240 represent chunks of five seconds (for timeout values between 5 seconds and 20 minutes); values from 241 to 251 are increments of 30 minutes (for 30 minutes to 5.5 hours). A value of 252 sets the timeout to 21 minutes, 253 to the vendor default, and 255 to 20 minutes and 15 seconds.
-T: Time cache reads to determine performance.
-t: Time device reads to determine performance.
-u [n]: Get or set the interrupt-unmask value for the drive. A value of 1 lets the drive unmask other interrupts and can improve performance; used with older kernels and hardware it can cause data loss.
-U: Unregister an IDE interface. Use this feature and the -R feature only with hot-swappable hardware, such as very high-end servers and some laptops. It can damage or hang other systems and should be used with caution.
-v: Display all appropriate settings for device except -i.
-W: Enable or disable the write-cache feature for the drive. The default varies between drive manufacturers.
-X n: Set the IDE transfer mode. Possible values include 34 (multiword DMA mode2 transfers) and 66 (UltraDMA mode2 transfers), or any PIO mode number plus 8. This option is suggested for experts only, and is useful only with newer EIDE/IDE/ATA2 drives. Often used in combination with -d.
-y: Put the IDE drive into standby (spin-down) mode, saving power.
-Y: Put the IDE drive into sleep mode.
-z: Force kernel to reread the partition table.
-Z

head

head [options] [files]

Print the first few lines (default is 10) of one or more files. If files is missing or -, read from standard input. With more than one file, print a header for each file.

Options

-c num[b|k|m], --bytes num [b|k|m]: Print first num bytes or, if num is followed by b, k, or m, first num 512-byte blocks, 1-kilobyte blocks, or 1-megabyte blocks.
--help: Display help and then exit.
-n num, --lines num, -num: Print first num lines. Default is 10.
-q, --quiet, --silent: Quiet mode; never print headers giving filenames.
-v, --verbose: Print filename headers, even for only one file.
--version: Output version information and then exit.

Examples

Display the first 20 lines of phone_list:

head -20 phone_list

Display the first 10 phone numbers having a 202 area code:

grep '(202)' phone_list | head

hexdump

hexdump [options] file

Display specified file or input in hexadecimal, octal, decimal, or ASCII format. Option flags are used to specify the display format.

Options

-b

Use a one-byte octal display, meaning the input offset is in hexadecimal and followed by sixteen three-column octal data bytes, filled in with zeroes and separated by spaces.

-c

Use a one-byte character display, meaning the input offset is in hexadecimal and followed by sixteen three-column entries, filled in with zeroes and separated with spaces.

-C

Canonical mode. Display hexadecimal offset, two sets of eight columns of hexadecimal bytes, then a | followed by the ASCII representation of those same bytes.

-d

Use a two-byte decimal display. The input offset is again in hexadecimal, but the display has only eight entries per line, of five columns each, containing two bytes of unsigned decimal format.

-e format_string

Choose a format string to be used to transform the output data. Format strings consist of:

Iteration count: The iteration count is optional. It determines the number of times to use the transformation string. The number should be followed by a slash character (/) to distinguish it from the byte count.
Byte count: The number of bytes to be interpreted by the conversion string. It should be preceded by a slash character to distinguish it from the iteration count.
Format characters: The actual format characters should be surrounded by quotation marks and are interpreted as fprintf (see printf) formatting strings, although the *, h, l, n, p, and q options will not work as expected. Format string usage is discussed at greater length in the hexdump manpage.

-f filename

Choose a file that contains several format strings. The strings should be separated by newlines; the # character marks a line as a comment.

-n length

Limit the number of bytes of input to be interpreted.

-o

Two-byte octal display, meaning a hexadecimal offset followed by eight five-column data entries of two bytes each, in octal format.

-s offset

Skip to specified offset. The offset number is assumed to be decimal unless it starts with 0x or 0X (hexadecimal), or O (octal). Numbers may also be designated in megabytes, kilobytes, or half-kilobytes with the addition of m, k, or b at the end of the number.

-v

Display all input data, even if it is the same as the previous line. Normally, a duplicate line is replaced by an asterisk (*).

-x

Display data in a two-byte hexadecimal format. The offset is, as usual, in hexadecimal, and is followed by eight space-separated entries, each of which contains four-column, two-byte chunks of data in hexadecimal format.

host

host [options] name [server]

System administration command. Print information about hosts or zones in DNS. Hosts may be IP addresses or hostnames; host converts IP addresses to hostnames by default and appends the local domain to hosts without a trailing dot. Default servers are determined in /etc/resolv.conf. For more information about hosts and zones, read Chapters 1 and 2 of DNS and BIND (O'Reilly).

Options

-a: Same as -t ANY.
-c class: Search for specified resource record class (IN, CH, CHAOS, HS, HESIOD, or ANY). Default is IN.
-d: Verbose output. Same as -v.
-l: Perform reverse lookups for IPv6 addresses using IP6.INT domain and "nibble" labels instead of IP6.ARPA and binary labels.
-n: Perform zone transfer. Same as -t AXFR.
-r: Do not ask contacted server to query other servers, but require only the information that it has cached.
-t type: Look for type entries in the resource record. type may be any recognized query type, such as A, AXFR, CNAME, NS, SOA, SIG, or ANY. If name is a hostname, host will look for A records by default. If name is an IPv4 or IPv6 address, it will look for PTR records.
-v: Verbose. Include all fields from resource record, even time-to-live and class, as well as "additional information" and "authoritative nameservers" (provided by the remote nameserver).
-w: Never give up on queried server.
-C: Display SOA records from all authoritative name servers for the specified zone.
-N n: Consider names with fewer than n dots in them to be relative. Search for them in the domains listed in the search and domain directives of /etc/resolv.conf. The default is usually 1.
-R n: Retry query a maximum of n times. The defalt is 1.
-T: Use TCP instead of UDP to query name server. This is implied in queries that require TCP, such as AXFR requests.
-W n: Wait a maximum of n seconds for reply.

hostid

hostid

Print the ID number in hexadecimal of the current host.

hostname

hostname [option] [nameofhost]

Set or print name of current host system. A privileged user can set the hostname with the nameofhost argument.

Options

-a, --alias: Display the alias name of the host (if used).
-d, --domain: Print DNS domain name.
-f, --fqdn, --long: Print fully qualified domain name.
-F file, --file file: Consult file for hostname.
-h, --help: Print a help message and then exit.
-i, --ip-address: Display the IP address(es) of the host.
-n, --node: Display or set the DECnet node name.
-s, --short: Trim domain information from the printed name.
-v, --verbose: Verbose mode.
-V, --version: Print version information and then exit.
-y, --yp, --nis: Display the NIS domain name. A privileged user can set a new NIS domain name with nameofhost.

htdigest

htdigest [-c] filename realm username

Create or update user authentication files used by the Apache web server. The -c option is used if you wish to create the file, and will overwrite any existing files rather than update them. The three arguments are the file you wish to use as the authentication file, the realm name to which the user belongs, and the username you will update in the password file. You will be prompted for a password when you run the command.

The Apache manual contains information about authentication mechanisms, including more detail about using htdigest and the ways in which you can control access to the resources served by Apache.

hwclock

hwclock [option]

System administration command. Read or set the hardware clock. This command maintains change information in /etc/adjtime, which can be used to adjust the clock based on how much it drifts over time. hwclock replaces the clock command. The single-letter options are included for compatibility with the older command.

Options

You may specify only one of the following options:

-a, --adjust: Adjust the hardware clock based on information in /etc/adjtime and set the system clock to the new time.
--getepoch: Print the kernel's hardware clock epoch value, then exit.
-r, --show: Print the current time stored in the hardware clock.
-s, --hctosys: Set the system time in accordance with the hardware clock.
--setepoch, --epoch=year: Set the hardware clock's epoch to year.
--set --date=date: Set the hardware clock to the specified date, a string appropriate for use with the date command.
-v, --version: Print version and exit.
-w, --systohc: Set the hardware clock in accordance with the system time.

The following may be used with the above options.

--debug: Print information about what hwclock is doing.
--localtime: The hardware clock is stored in local time.
--noadjfile: Disable /etc/adjtime facilities.
--test: Do not actually change anything. This is good for checking syntax.
-u, --utc: The hardware clock is stored in Universal Coordinated Time.

iconv

iconv [options] files

Convert the contents of one or more files from one character encoding to another and write the results to standard output.

Options

-c: Omit invalid output characters.
-f code1, --from-code=code1: Convert input characters from the code1 encoding.
-?, --help: Print help message and exit.
-l, --list: Print a list of valid encodings to standard output.
-o file, --output=file: Write the converted output to file instead of standard output.
-s, --silent: Operate silently; don't print warning messages.
-t code2, --to-code=code2: Convert input characters to the code2 encoding.
--usage: Print a brief usage message showing only the command syntax and then exit.
-V, --version: Print version information and exit.
--verbose: Operate verbosely; print progress messages.

id [options] [username]

Display information about yourself or another user: user ID, group ID, effective user ID and group ID if relevant, and additional group IDs.

Options

-g, --group: Print group ID only.
-G, --groups: Print supplementary groups only.
-n, --name: With -u, -g, or -G, print user or group name, not number.
-r, --real: With -u, -g, or -G, print real, not effective, user ID or group ID.
-u, --user: Print user ID only.
--help: Print help message and then exit.
--version: Print version information.

identd

in.identd [options] [kernelfile [kmemfile]]

TCP/IP command. Provide the name of the user whose process is running a specified TCP/IP connection. You may specify the kernel and its memory space.

Options

-b: Run standalone; not for use with inetd.
-d: Allow debugging requests.
-ggid: Attempt to run in the group gid. Useful only with -b.
-h: Print help message, then exit.
-i: Run as a daemon, one process per request.
-l: Run using init.
-m: Allow multiple requests per session.
-n: Return user IDs instead of usernames.
-o: When queried for the type of operating system, always return OTHER.
-pport: Listen at port instead of the default, port 113.
-tseconds: Exit if no new requests have been received before seconds seconds have passed. Note that, with -i or -w, the next new request will result in identd being restarted. Default is infinity (never exit).
-uuid: Attempt to run as uid. Useful only with -b.
-w: Run as a daemon, one process for all requests.
-Cfile: Read configuration information from file instead of /etc/identd.conf.
-E: Enable DES encryption using the last key from key file /etc/identd.key.
-Kn: Use a maximum of n threads to perform kernel lookups. Default is 8.
-Lfacility: Use the specified syslog facility instead of daemon.key.
-N: Do not provide a username or user ID if the file .noident exists in the user's home directory.
-Pfile: Store the process number for the identd daemon in file. By default it's /etc/identd.pid.
-V: Print version and exit.

ifconfig

ifconfig [interface]
ifconfig [interface address_family parameters addresses]

TCP/IP command. Assign an address to a network interface and/or configure network interface parameters. ifconfig is typically used at boot time to define the network address of each interface on a machine. It may be used at a later time to redefine an interface's address or other parameters. Without arguments, ifconfig displays the current configuration for a network interface. Used with a single interface argument, ifconfig displays that particular interface's current configuration.

Arguments

interface: String of the form name unit, for example, en0.
address_family: Since an interface may receive transmissions in differing protocols, each of which may require separate naming schemes, you can specify the address_family to change the interpretation of the remaining parameters. You may specify inet (for TCP/IP, the default), ax25 (AX.25 Packet Radio), ddp (Appletalk Phase 2), or ipx (Novell).
parameters

imake

imake options

C preprocessor (cpp) interface to the make utility. imake ("include make") solves the portability problem of make by allowing machine dependencies to be kept in a central set of configuration files, separate from the descriptions of the various items to be built. The targets are contained in the Imakefile, a machine-independent description of the targets to be built, written as cpp macros. imake uses cpp to process the configuration files and the Imakefile, and to generate machine-specific Makefiles, which can then be used by make.

One of the configuration files is a template file, a master file for imake. This template file (default is Imake.tmpl) #includes the other configuration files that contain machine dependencies such as variable assignments, site definitions, and cpp macros, and directs the order in which the files are processed. Each file affects the interpretation of later files and sections of Imake.tmpl. Comments may be included in imake configuration files, but the initial # needs to be preceded with an empty C comment:

/**/#

For more information, see cpp and make. Also check out the Nutshell Handbook Software Portability with imake (O'Reilly).

Options

-e: Execute the generated Makefile. Default is to leave this to the user.
-f filename: Name of per-directory input file. Default is Imakefile.
-s filename: Name of make description file to be generated. If filename is a -, the output is written to stdout. The default is to generate, but not execute, a Makefile.
-v: Print the cpp command line used to generate the Makefile.
-C filename: Use the specified name for the temporary input file for cpp instead of the default Imakefile.c.
-Ddefine: Set directory-specific variables. This option is passed directly to cpp.
-Idirectory: Directory in which imake template and configuration files may be found. This option is passed directly to cpp.
-Ttemplate: Name of master template file used by cpp. This file is usually located in the directory specified with the -I option. The default file is Imake.tmpl.
-Udefine: Unset directory-specific variables. This option is passed directly to cpp.

Tools

Following is a list of tools used with imake:

makedepend [options] files

Create header file dependencies in Makefiles. make depend reads the named input source files in sequence and parses them to process #include, #define, #undef, #ifdef, #ifndef, #endif, #if, and #else directives so that it can tell which #include directives would be used in a compilation. makedepend determines the dependencies and writes them to the Makefile. make then knows which object files must be recompiled when a dependency has changed. makedepend has the following options:

-- options --: Ignore any unrecognized options following a double hyphen. A second double hyphen terminates this action. Recognized options between the hyphens are processed normally.
-a: Append dependencies to any existing ones instead of replacing existing ones.
-ffilename: Write dependencies to filename instead of to Makefile.
-m: Print a warning when encountering a multiple inclusion.
-o suffix: Specify an object file suffix to use instead of the default .o.
-p prefix: Specify a prefix to prepend to object names. The prefix may be a directory.
-sstring: Use string as delimiter in file, instead of # DO NOT DELETE THIS LINE -- make depend depends on it.
-v: Verbose. List all files included by main source file.
-w n: Format output no wider than n characters. Default is 78.
-Dname: Define name with the given value (first form) or with value 1 (second form).
-Idir: Add directory dir to the list of directories searched.
-Ydir: Search only dir for include files. Ignore standard include directories.

mkdirhier dir...

Create directory dir and all missing parent directories during file installation operations.

xmkmf [option] [topdir] [curdir]

Bootstrap a Makefile from an Imakefile. topdir specifies the location of the project root directory. curdir (usually omitted) is specified as a relative pathname from the top of the build tree to the current directory. The -a option is equivalent to the following command sequence:

% xmkmf
% make Makefiles
% make includes
% make depend

Configuration files

Following is a list of the imake configuration files:

Imake.tmpl: Master template for imake. Imake.tmpl includes all the other configuration files, plus the Imakefile in the current directory.
Imake.params: Contains definitions that apply across sites and vendors.
Imake.rules: Contains cpp macro definitions that are configured for the current platform. The macro definitions are fed into imake, which runs cpp to process the macros. Newlines (line continuations) are indicated by the string @@\ (double at sign, backslash).
site.def: Contains site-specific (as opposed to vendor-specific) information, such as installation directories, what set of programs to build, and any special versions of programs to use during the build. The site.def file changes from machine to machine.
Project.tmpl: File containing X-specific variables.
Library.tmpl: File containing library rules.
Server.tmpl: File containing server-specific rules.
.cf: The .cf files are the vendor-specific VendorFiles that live in Imake.vb. A .cf file contains platform-specific definitions, such as version numbers of the operating system and the compiler and workarounds for missing commands. The definitions in .cf files override the defaults, defined in Imake.params.

The Imakefile

The Imakefile is a per-directory file that indicates targets to be built and installed and rules to be applied. imake reads the Imakefile and expands the rules into Makefile target entries. An Imakefile may also include definitions of make variables and list the dependencies of the targets. The dependencies are expressed as cpp macros, defined in Imake.rules. Whenever you change an Imakefile, you need to rebuild the Makefile and regenerate header file dependencies. For more information on imake, see Software Portability with imake (O'Reilly).

imapd

imapd

TCP/IP command. The Interactive Mail Access Protocol (IMAP) server daemon. imapd is invoked by inetd and listens on port 143 for requests from IMAP clients. IMAP allows mail programs to access remote mailboxes as if they were local. IMAP is a richer protocol than POP because it allows a client to retrieve message-level information from a server mailbox instead of the entire mailbox. IMAP can be used for online and offline reading. The popular Pine mail client contains support for IMAP.

inetd

inetd [options] [configuration_file]

TCP/IP command. The internet services daemon. (On some systems this command is replaced by xinetd.) Initialized at bootup, inetd creates sockets on behalf of other services and listens to them simultaneously. When it receives an incoming connection request, it spawns the appropriate server and passes it the connection.

The following servers are commonly started by inetd: bootpd, bootpgw, fingerd, ftpd, imapd, rexecd, rlogind, rshd, talkd, telnetd, and tftpd. In addition to launching other services, inetd runs a few basic services of its own, including daytime, which returns the system's time of day, and chargen, which generates a string of characters.

Configuration file

inetd reads information on the services it should support from the specified configuration_file, or from the default configuration file /etc/inetd.conf. inetd rereads its configuration file when it receives a hangup signal, SIGHUP. Services may be added, deleted, or modified when the configuration file is reread. Lines beginning with # are treated as comments. Each entry in the configuration file is a single line composed of the following fields:

service: The service name as found in /etc/services.
type: Socket type, either stream for TCP-based services or dgram for UDP-based services.
protocol: The transport protocol used by the service. This must be a protocol found in /etc/protocols. It's usually either tcp or udp.
wait: For dgram sockets, this field specifies whether inetd should wait until the service is done to listen on the socket again, or should resume listening right away. The value can be either wait or nowait. Single-threaded servers like most RPC servers should use wait. Multithreaded servers should use nowait.
user: The user ID the process should run under. May be given a name or number. To specify a group name as well, append a dot (.) to the user ID, followed by the group ID.
server: The full path to the server program to be executed. For inetd's own services, the value of this field is internal. Many entries specify the TCP logging tool tcpd in this field to wrap the server whose command is given in the next field.
cmdline: The command-line arguments to be passed to the server, beginning with the name of the server program itself (argv[0]). inetd's internal services have no command lines.

Options

-d: Turn on socket-level debugging and print debugging information to stdout.
-q length: Specify the maximum number of pending connections to allow in a socket queue. The default is 128. The minimum value is 8.

Files

/etc/inetd.conf: Default configuration file.
/var/run/inetd.pid: inetd's process ID.

info

`info [options] [topics]

GNU hypertext reader. Display online documentation previously built from Texinfo input. Info files are arranged in a hierarchy and can contain menus for subtopics. When entered without options, the command displays the top-level info file (usually /usr/local/info/dir). When topics are specified, find a subtopic by choosing the first topic from the menu in the top-level info file, the next topic from the new menu specified by the first topic, and so on. The initial display can also be controlled by the -f and -n options. If a specified topic has no info file but does have a manpage, info displays the manpage; if there is neither, the top-level info file is displayed.

Options

-d directories, --directory directories: Search directories, a colon-separated list, for info files. If this option is not specified, use the INFOPATH environment variable or the default directory (usually /usr/local/info).
--dribble file: Store each keystroke in file, which can be used in a future session with the --restore option to return to this place in info.
-f file, --file file: Display specified info file.
-n node, --node node: Display specified node in the info file.
-o file, --output file: Copy output to file instead of displaying it at the screen.
--help: Display brief help.
--restore file: When starting, execute keystrokes in file.
--subnodes: Display subtopics.
--version: Display version.
--vi-keys: Use vi-like key bindings.

init

init [bootflags] [runlevel]

System administration command. Initialize system.

Boot flags

-a: Set the AUTOBOOT environment variable to yes. The boot loader will do this automatically when booting with the default command line.
-b: Boot directly into a single user shell for emergency recovery.
-z characters: The specified characters are ignored, but will make the command line take up a bit more room on the stack. init uses the extra space to show the curent runlevel when running the ps command.

Files

init is the first process run by any Unix machine at boot time. It verifies the integrity of all filesystems and then creates other processes, using fork and exec, as specified by /etc/inittab. Which processes may be run are controlled by runlevel. All process terminations are recorded in /var/run/utmp and /var/log/wtmp. When the runlevel changes, init sends SIGTERM and then, after 20 seconds, SIGKILL to all processes that cannot be run in the new runlevel.

Runlevels

The current runlevel may be changed by telinit, which is often just a link to init. The default runlevels vary from distribution to distribution, but these are standard:

0: Halt the system.
1, s, S: Single-user mode.
6: Reboot the system.
q, Q: Reread /etc/inittab.

Check the /etc/inittab file for runlevels on your system.

insmod

insmod [options] file [symbol=value ...]

System administration command. Load the module file into the kernel, changing any symbols that are defined on the command line. If the module file is named file.o or file.mod, the module will be named file.

Options

-e file, --persist=file: Read persistent data from file. If module has no persistent data, this option is ignored. If the file parameter is the null string "", use default file location.
-f, --force: Force loading of module, even if problems are encountered.
-h, --help: Print help message, then exit.
-k, --autoclean: Mark module to be removed when inactive.
-m, --map: Print a load map to standard output.
-n, --noload: Do everything needed to load file, but do not load it. Used to debug command line.
-o name, --name=name: Name module name instead of using the object file's name.
-p, --probe: Check to see that the module can be successfully loaded.
-q, --quiet: Don't print warnings or error messages.
-r, --root: Load modules not owned by the root account. By default these are rejected. This is a security risk.
-s, --syslog: Send messages to syslog instead of standard output.
-v, --verbose: Print additional information about progress of insmod.
-x, --noexport: If module does not explicitly export its own symbol table, do not export modules' external symbols.
-y, --noksymoops: Do not add symbols used for debugging Oops to ksyms. These are required if the module has persistent data.
-L, --lock: Set a file lock on the module.
-N, --numeric-only: When checking the module version against the kernel version, only check the numeric part. This is the default for kernel version 2.5 or later.
-O file, --blob=file: Save binary blob of what is loaded into the kernel to file.
-P prefix, --prefix=prefix: Specify symbol versions to prefix to module names.
-S, --Kallsyms: Always load modules with kallsyms data, even when the kernel does not support it.
-X, --export: If module does not explicitly export its own symbol table, export all modules' external symbols. This is the default behavior.
-V, --version: Print version, then exit.
-Y, --ksymoops: Add symbols used for debugging Oops to ksyms. These are required if the module has persistent data.

install

install [options] [source] destination

System administration command. Used primarily in Makefiles to update files. install copies files into user-specified directories. Similar to cp, but attempts to set permission modes, owner, and group. The source may be a file or directory, or a list of files and directories. The destination should be a single file or directory.

Options

-b, --backup[=control]

Back up any existing files. When using the long version of the command, the optional control parameter controls the kind of backup. When no control is specified, install will attempt to read the control value from the VERSION_CONTROL environment variable. Accepted values are:

none, off: Never make backups.
numbered, t: Make numbered backups.
existing, nil: Match existing backups, numbered or simple.
simple, never: Always make simple backups.

-d, --directory

Create any missing directories.

-g group, --group group

Set group ID of new file to group (privileged users only).

--help

Set permissions of new file to mode (octal or symbolic). By default, the mode is 0755.

-m mode, --mode mode

-o [owner], --owner[=owner]

Set ownership to owner or, if unspecified, to root (privileged users only).

-p, --preserve-timestamps

Preserve access and modification times on source files and directories.

-s, --strip

Strip symbol tables.

-v, --verbose

Print name of each directory as it is created.

--version

Print version, then exit.

-C

Do not overwrite file when the target exists and is identical to the new file. Preserve original timestamp.

-D

Create leading components of destination except the last, then copy source to destination.

-S suffix, --suffix=suffix

Use suffix instead of the default backup suffix, usually ~.

ipchains

ipchains command [options]

System administration command. Edit IP firewall rules in the 2.2 Linux kernel. A 2.2 Linux kernel compiled with firewall support will examine the headers of all network packets and compare them to matching rules to see what it should do with the packet. A firewall rule consists of some matching criteria and a target, which is a result to be applied if the packet matches the criteria. The rules are organized into chains. You can use these rules to build a firewall or just reject certain kinds of network connections.

Firewall rules are organized into chains, ordered checklists that the kernel works through looking for matches. There are three built-in chains: input, output, and forward. Packets entering the system are tested against the input chain; those exiting the system are checked against the output chain. If an incoming packet is destined for some other system, it is checked against the forward chain. Each of these chains has a default target (a policy) in case no match is found. User-defined chains can be created and used as targets for packets, but they have no default policies. If no match can be found in a user-defined chain, the packet is returned to the chain from which it was called and tested against the next rule in that chain.

ipchains changes only the rules in the running kernel. When the system is powered off, all those changes are lost. You can use the ipchains-save command to make a script you can later run with ipchains-restore to restore your firewall settings. Such a script is often called at bootup, and many distributions have an ipchains initialization script that uses the output from ipchains-save.

Commands

ipchains is always invoked with one of the following commands:

-A chain rules, --append chain rules: Append new rules to chain.
-I chain number rules, --insert chain number rules: Insert rules into chain at the ordinal position given by number.
-D chain rules, --delete chain rules: Delete rules from chain. Rules can be specified by their ordinal number in the chain as well as by a general rule description.
-R chain number rule, --replace chain number rule: Replace a rule in chain. The rule to be replaced is specified by its ordinal number.
-C chain rule, --check chain rules: Construct a network packet that matches the given rule and check how chain will handle it. The rule must describe the source, destination, protocol, and interface of the packet to be constructed.
-L [chain], --list $PARAMETER: List the rules in chain. If no chain is specified, list the rules in all chains.
-ML, --masquerading --list: List masquerading connections.
-MS tcp tcpfin udp, --masquerading --set tcp tcpfin udp: Set timeout value in seconds for masquerading connections. -MS always takes three parameters, specifying the timeout values for TCP sessions, for TCP sessions that have received a FIN packet, and for UDP packets.
-F chain, --flush chain: Remove all rules from chain.
-Z [chain], --zero [chain]: Reset the packet and byte counters in chain. If no chain is specified, all chains will be reset. When used without specifying a chain and combined with the -L command, lists the current counter values before they are reset.
-N chain, --new-chain chain: Create a new chain. The chain's name must be unique.
-X [chain], --delete-chain chain: Delete chain. Only user-defined chains can be deleted, and there can be no references to the chain to be deleted. If no argument is given, all user-defined chains will be deleted.
-P chain target, --policy chain target: Set the policy for a built-in chain; the target itself cannot be a chain.
-S tcp tcpfin udp, --set tcp tcpfin udp: Set masquerade timeout values for TCP sessions, TCP sessions after receiving a FIN packet, and UDP sessions. Timeout values of 0 preserve the previous setting. This option valid only when used with -M.
-h [icmp]: Print a brief help message. If the option icmp is given, print a list of valid ICMP types.
-V, --version: Print version number, then exit.

Targets

A target can be the name of a chain or one of the following special values:

ACCEPT: Let the packet through.
DENY: Drop the packet.
MASQ: Masquerade the packet so it appears that it originated from the current system. Reverse packets from masqueraded connections are unmasqueraded automatically. This is a legal target only for the forward chain, or user-defined chains used in forwarding packets. To use this target, the kernel must be compiled with support for IP masquerading.
REDIRECT [port]: Redirect incoming packets to a local port on which you are running a transparent proxy program. If the specified port is 0 or is not given, the destination port of the packet is used as the redirection port. REDIRECT is a legal target only for the input chain or for user-defined chains used in handling incoming packets. The kernel must be compiled with support for transparent proxies.
REJECT: Drop the packet and send an ICMP message back to the sender indicating that the packet was dropped.
RETURN: Return to the chain from which this chain was called and check the next rule. If RETURN is the target of a rule in a built-in chain, then the built-in chain's default policy is applied.

Rule specification parameters

These options are used to create rules for use with the preceding commands. Rules consist of some matching criteria and usually a target to jump to (-j) if the match is made. Many of the parameters for these matching rules can be expressed as a negative with an exclamation point (!) meaning "not." Those rules will match everything except the given parameter.

-p [!] name, --protocol [!]$PARAMETER: Match packets of protocol name. The value of name can be given as a name or number as found in the file /etc/protocols. The most common values are tcp, udp, icmp, or the special value all. The number 0 is equivalent to all, and this is the default value when this option is not used.
-s [!] address[/mask] [!] [port], --source [!] address[/mask] [!] [port]: Specifies the source address and port of the packet that will match this rule. The address may be supplied as a hostname, a network name, or an IP address. The optional mask is the netmask to use and may be supplied either in the traditional form (e.g., /255.255.255.0) or in the modern form (e.g., /24). The optional port specifies the TCP, UDP, or ICMP type that will match. You may supply a port specification only if you've supplied the -p parameter with one of the tcp, udp or icmp protocols. A colon can be used to indicate an inclusive range of ports or ICMP values to be used (e.g., 20:25 for ports 20 through 25). If the first port parameter is missing, the default value is 0. If the second is omitted, the default value is 65535.
-d [!] address[/mask] [!] [port], --destination [!] address[/mask] [port]: Match packets with the destination address. The syntax for this command's parameters is the same as for the -s option.
-j target, --jump target: Jump to a special target or a user-defined chain. If this option is not specified for a rule, matching the rule only increases the rule's counters and the packet is tested against the next rule.
-i [!] name, --interface name: Match packets from interface name[+]. name is the network interface used by your system (e.g., eth0 or ppp0). A + can be used as a wildcard, so ppp+ would match any interface name beginning with ppp.
[!] -f, [!]--fragment $PARAMETER: The rule applies to everything but the first fragment of a fragmented packet.
--source-port [!] port: Match packets from the source port. The syntax for specifying ports can be found in the preceding description of the -s option.
--destination-port [!] port: Match packets with the destination port. The syntax for specifying ports can be found in the preceding description of the -s option.
--icmp-type [!] type: Match packets with ICMP type name or number of type.

Options

-b, --bidirectional: Put rule in both the input and output chain so that packets will be matched in both directions.
-v, --verbose: Verbose mode.
-n, --numeric: Print all IP address and port numbers in numeric form. By default, names are displayed when possible.
-l, --log: Log information for the matching packet to the system log.
-t andmask xormask, --TOS andmask xormask: Change the Type Of Service field in the packet's header. The TOS field is first ANDed with the 8-bit hexadecimal mask andmask, then XORed with the 8-bit hexadecimal mask xormask. Rules that would affect the least significant bit (LSB) portion of the TOS field are rejected.
-x, --exact: Expand all numbers in a listing (-L). Display the exact values of the packet and byte counters instead of rounded figures.
[!] -y, --syn: Match only incoming TCP connection requests, those with the SYN bit set and the ACK and FIN bits cleared. This blocks incoming TCP connections but leaves outgoing connections unaffected.
--line-numbers: Used with the -L command. Add the line number to the beginning of each rule in a listing indicating its position in the chain.
--no-warnings

ipchains-restore

ipchains-restore [options]

System administration command. Restore firewall rules. ipchains-restore takes commands generated by ipchains-save and uses them to restore the firewall rules for each chain. Often used by initialization scripts to restore firewall settings on boot.

Options

-f: Force updates of existing chains without asking.
-v: Print rules as they are being restored.
-p: If a nonexisting chain is targeted by a rule, create it.

ipchains-save

ipchains-save [chain] [option]

System administration command. Print the IP firewall rules currently stored in the kernel to stdout. If no chain is given, all chains will be printed. Output is usually redirected to a file, which can later be used by ipchains-restore to restore the firewall.

Option

- v: Print out rules to stderr as well as stdout, making them easier to see when redirecting output.

ipcrm

ipcrm [options]

System administration command. Remove interprocess communication (IPC) message queues, shared memory segments, or semaphore arrays. These may be specified either by numeric identifier or by key, using the following options.

Options

-m identifier, -M key: Remove specified shared memory segment and its associated data structures after the last detach is performed.
-q identifier, -Q key: Remove specified message queue and its associated data structures.
-s identifier, -S key: Remove specified semaphore array and its associated data structures.

ipcs

ipcs [options]

System administration command. Print report on interprocess communication (IPC) message queues, shared memory segments, and semaphore arrays for which the current process has read access. Options can be used to specify the type of resources to report on and the output format of the report.

Options

Resource specification options:

-a: Report on all IPC facilities: shared memory segments, message queues, and semaphore arrays. This is the default.
-m: Report on shared memory segments.
-q: Report on message queues.
-s: Report on semaphore arrays.

Output format options:

-c: Print creator and owner user IDs for IPC facilities.
-l: Print resource maximum and minimum limits.
-p: Print creator and last operation process identifiers.
-t: Print attach, detach, and change times for shared memory segments, last operation and change times for semaphore arrays, and send, receive, and change times for message queues.
-u: Print summary of current resource usage.

Other options:

-h: Print help message, then exit.
-i identifier: Used in combination with the -m, -q, or -s options. Report only on the resource specified by numeric identifier.

iptables

iptables command [options]

System administration command. Configure netfilter filtering rules. In the 2.4 kernel, the ipchains firewall capabilities are replaced with the netfilter kernel module. netfilter can be configured to work just like ipchains, but it also comes with the module iptables, which is similar to ipchains but extensible. iptables rules consist of some matching criteria and a target, a result to be applied if the packet matches the criteria. The rules are organized into chains. You can use these rules to build a firewall, masquerade your local area network, or just reject certain kinds of network connections.

There are three built-in tables for iptables: one for network filtering (filter), one for Network Address Translation (nat), and the last for specialized packet alterations (mangle). Firewall rules are organized into chains, ordered checklists of rules that the kernel works through looking for matches. The filter table has three built-in chains: INPUT, OUTPUT, and FORWARD. The INPUT and OUTPUT chains handle packets originating from or destined for the host system. The FORWARD chain handles packets just passing through the host system. The nat table also has three built-in chains: PREROUTING, POSTROUTING, and OUTPUT. mangle has only two chains: PREROUTING and OUTPUT.

netfilter checks packets entering the system. After applying any PREROUTING rules, it passes them to the INPUT chain, or to the FORWARD chain if the packet is just passing through. Upon leaving, the system packets are passed to the OUTPUT chain and then on to any POSTROUTING rules. Each of these chains has a default target (a policy) in case no match is found. User-defined chains can also be created and used as targets for packets but do not have default policies. If no match can be found in a user-defined chain, the packet is returned to the chain from which it was called and tested against the next rule in that chain.

iptables changes only the rules in the running kernel. When the system is powered off, all changes are lost. You can use the iptables-save command to make a script you can run with iptables-restore to restore your firewall settings. Such a script is often called at bootup. Many distributions have an iptables initialization script that uses the output from iptables-save.

Commands

iptables is always invoked with one of the following commands:

-A chain rules, --append chain rules: Append new rules to chain.
-I chain number rules, --insert chain number rules: Insert rules into chain at the ordinal position given by number.
-D chain rules, --delete chain rules: Delete rules from chain. Rules can be specified by their ordinal number in the chain as well as by a general rule description.
-R chain number rule, --replace chain number rule: Replace a rule in chain. The rule to be replaced is specified by its ordinal number.
-C chain rule, --check chain rules: Check how chain will handle a network packet that matches the given rule. The rule must describe the source, destination, protocol, and interface of the packet to be constructed.
-L [chain], --list $PARAMETER: List the rules in chain, or all chains if chain is not specified.
-F [chain], --flush chain: Remove all rules from chain, or from all chains if chain is not specified.
-Z [chain], --zero [chain]: Zero the packet and byte counters in chain. If no chain is specified, all chains will be reset. When used without specifying a chain and combined with the -L command, list the current counter values before they are reset.
-N chain, --new-chain chain: Create a new chain. The chain's name must be unique. This is how user-defined chains are created.
-X [chain], --delete-chain [chain]: Delete the specified user-defined chain, or all user-defined chains if chain is not specified.
-P chain target, --policy chain target: Set the default policy for a built-in chain; the target itself cannot be a chain.
-E old-chain new-chain, --rename-chain old-chain new-chain: Rename old-chain to new-chain.
-h [icmp]: Print a brief help message. If the option icmp is given, print a list of valid ICMP types.

Targets

A target may be the name of a chain or one of the following special values:

ACCEPT: Let the packet through.
DROP: Drop the packet.
QUEUE: Send packets to the user space for processing.
RETURN: Stop traversing the current chain and return to the point in the previous chain from which this one was called. If RETURN is the target of a rule in a built-in chain, the built-in chain's default policy is applied.

Rule specification parameters

-p [!] name, --protocol [!]$PARAMETER: Match packets of protocol name. The value of name can be given as a name or number as found in the file /etc/protocols. The most common values are tcp, udp, icmp, or the special value all. The number 0 is equivalent to all, and this is the default value when this option is not used. If there are extended matching rules associated with the specified protocol, they will be loaded automatically. You need not use the -m option to load them.
-s [!] address[/mask] [!] [port], --source [!] address[/mask] [!] [port]: Match packets with the source address. The address may be supplied as a hostname, a network name, or an IP address. The optional mask is the netmask to use and may be supplied either in the traditional form (e.g., /255.255.255.0) or in the modern form (e.g., /24).
-d [!] address[/mask] [!] [port], --destination [!] address[/mask] [port]: Match packets from the destination address. See the description of -s for the syntax of this option.
-j target, --jump target: Jump to a special target or a user-defined chain. If this option is not specified for a rule, matching the rule only increases the rule's counters, and the packet is tested against the next rule.
-i [!] name[+], --in-interface name[+]: Match packets being received from interface name. name is the network interface used by your system (e.g., eth0 or ppp0). A + can be used as a wildcard, so ppp+ would match any interface name beginning with ppp.
-o [!] name[+], --out-interface name[+]: Match packets being sent from interface name. See the description of -i for the syntax for name.
[!] -f, [!]--fragment $PARAMETER: The rule applies only to the second or further fragments of a fragmented packet.
-c packets bytes, --set-counters packets bytes: Initialize packet and byte counters to the specified values.

Options

-v, --verbose: Verbose mode.
-n, --numeric: Print all IP address and port numbers in numeric form. By default, text names are displayed when possible.
-x, --exact: Expand all numbers in a listing (-L). Display the exact value of the packet and byte counters instead of rounded figures.
-m module, --match module: Explicitly load matching rule extensions associated with module. See the next section.
-h [icmp], --help [icmp]: Print help message. If icmp is specified, a list of valid ICMP type names will be printed. -h can also be used with the -m option to get help on an extension module.
--line-numbers: Used with the -L command. Add the line number to the beginning of each rule in a listing, indicating its position in the chain.
--modprobe=command: Use specified command to load any necessary kernel modules while adding or inserting rules into a chain.

Match extensions

Several kernel modules come with netfilter to extend matching capabilities of rules. Those associated with particular protocols are loaded automatically when the -p option is used to specify the protocol. Others need to be loaded explicitly with the -m option.

tcp

Loaded when -p tcp is the only protocol specified.

--source-port [!] [port][:port], --sport [!] [port][:port]: Match the specified source ports. Using the colon specifies an inclusive range of services to match. If the first port is omitted, 0 is the default. If the second port is omitted, 65535 is the default. You can also use a dash instead of a colon to specify the range.
--destination-port [!] [port][:port], --dport [!] [port][:port]: Match the specified destination ports. The syntax is the same as for --source-port.
--tcp-flags [!] mask comp: Match the packets with the TCP flags specified by mask and comp. mask is a comma-separated list of flags that should be examined. comp is a comma-separated list of flags that must be set for the rule to match. Valid flags are SYN, ACK, FIN, RST, URG, PSH, ALL, and NONE.
--tcp-option [!] n: Match if TCP option is set.
--mss n[:n]: Match if TCP SYN or SYN/ACK packets have the specified MSS value or fall within the specified range. Use this to control the maximum packet size for a connection.
[!] --syn: Match packets with the SYN bit set and the ACK and FIN bits cleared. These are packets that request TCP connections; blocking them prevents incoming connections. Shorthand for --tcp-flags SYN,RST,ACK SYN.

udp

Loaded when -p udp is the only protocol specified.

--source-port [!] [port][:port], --sport [!] [port][:port]: Match the specified source ports. The syntax is the same as for the --source-port option of the TCP extension.
--destination-port [!] [port][:port], --dport [!] [port][:port]: Match the specified destination ports. The syntax is the same as for the --source-port option of the TCP extension.

icmp

Loaded when -p icmp is the only protocol specified.

--icmp-type [!] type: Match the specified ICMP type. type may be a numeric ICMP type or one of the ICMP type names shown by the command iptables -p icmp -h.

mac

Loaded explicitly with the -m option.

--mac-source [!] address: Match the source address that transmitted the packet. address must be given in colon-separated hexbyte notation (for example, --mac-source 00:60:08:91:CC:B7).

limit

Loaded explicitly with the -m option. The limit extensions are used to limit the number of packets matched. This is useful when combined with the LOG target. Rules using this extension match until the specified limit is reached.

--limit rate: Match addresses at the given rate. rate is specified as a number with an optional /second, /minute, hour, or /day suffix. When this option is not set, the default is 3/hour.
--limit-burst [number]: Set the maximum number of packets to match in a burst. Once the number has been reached, no more packets are matched for this rule until the number has recharged. It recharges at the rate set by the --limit option. When not specified, the default is 5.

multiport

Loaded explicitly with the -m option. The multiport extensions match sets of source or destination ports. These rules can be used only in conjunction with -p tcp and -p udp. Up to 15 ports can be specified in a comma-separated list.

--source-port [ports]: Match the given source ports.
--destination-port [ports]: Match the given destination ports.
--port [ports]: Match if the packet has the same source and destination port and that port is one of the given ports.

mark

Loaded explicitly with the -m option. This module works with the MARK extension target.

--mark value[/mask]: Match the given unsigned mark value. If a mask is specified, it is logically ANDed with the mark before comparison.

owner

Loaded explicitly with the -m option. The owner extensions match the user, group, process, and session IDs of a local packet's creator. This makes sense only as a part of the OUTPUT chain.

--uid-owner userid: Match packets created by a process owned by userid.
--gid-owner groupid: Match packets created by a process owned by groupid.
--pid-owner processid: Match packets created by process ID processid.
--sid-owner sessionid: Match packets created by a process in the session sessionid.
--cmd-owner command: Match if packet was created by a process with the name command.

state

Loaded explicitly with the -m option. This module matches the connection state of a packet.

--state states: Match the packet if it has one of the states in the comma-separated list states. Valid states are INVALID, ESTABLISHED, NEW, and RELATED.

tos

Loaded explicitly with the -m option. This module matches the Type of Service field in a packet's header.

--tos value: Match the packet if it has a TOS of value. value can be a numeric value or a Type of Service name. iptables -m tos -h will give you a list of valid TOS values.

tostate

Loaded explicitly with the -m option. This module matches the connection state of a packet.

--state states: Match the packet if it has one of the states in the comma-separated list states. Valid states are INVALID, ESTABLISHED, NEW, and RELATED.

ah

Loaded explicitly with the -m option. This module matches the SPIs in the AH header of IPSec packets.

--ahspi [!] n[:n]: Match the SPIs in the AH header against the specified value or range of values.

esp

Loaded explicitly with the -m option. This module matches the SPIs in the ESP header of IPSec packets.

--ahspi [!] n[:n]: Match the SPIs in the ESP header against the specified value or range of values.

length

Loaded explicitly with the -m option. This module matches the length of a packet.

--length n[:n]: Match if the length of the packet is the same as the specified value or is within the range of values.

ttl

Loaded explicitly with the -m option. This module matches the time-to-live (TTL) field in the IP header.

--ttl n: Match if the TTL is the same as the specified value.

Target extensions

Extension targets are optional additional targets supported by separate kernel modules. They have their own associated options.

LOG

Log the packet's information in the system log.

--log-level level: Set the syslog level by name or number (as defined by syslog.conf).
--log-prefix prefix: Begin each log entry with the string prefix. The prefix string may be up to 30 characters long.
--log-tcp-sequence: Log the TCP sequence numbers. This is a security risk if your log is readable by users.
--log-tcp-options: Log options from the TCP packet header.
--log-ip-options: Log options from the IP packet header.

MARK

Used to mark packets with an unsigned integer value you can use later with the mark matching extension. Valid only with the mangle table.

--set-mark value: Mark the packet with value.

REJECT

Drop the packet and, if appropriate, send an ICMP message back to the sender indicating the packet was dropped. If the packet was an ICMP error message, an unknown ICMP type, or a nonhead fragment, or if too many ICMP messages have already been sent to this address, no message is sent.

--reject-with type: Send specified ICMP message type. Valid values are icmp-net-unreachable, icmp-host-unreachable, icmp-port-unreachable, or icmp-proto-unreachable. If the packet was an ICMP ping packet, type may also be echo-reply.

TOS

Set the Type of Service field in the IP header. TOS is a valid target only for rules in the mangle table.

--set-tos value: Set the TOS field to value. You can specify this as an 8-bit value or as a TOS name. You can get a list of valid names using iptables -j TOS -h.

SNAT

Modify the source address of the packet and all future packets in the current connection. SNAT is valid only as a part of the POSTROUTING chain in the nat table.

--to-source address[-address][port-port]: Specify the new source address or range of addresses. If a tcp or udp protocol has been specified with the -p option, source ports may also be specified. If none is specified, map the new source to the same port if possible. If not, map ports below 512 to other ports below 512, those between 512 and 1024 to other ports below 1024, and ports above 1024 to other ports above 1024.

DNAT

Modify the destination address of the packet and all future packets in the current connection. DNAT is valid only as a part of the POSTROUTING chain in the nat table.

--to-destination address[-address][port-port]: Specify the new destination address or range of addresses. The arguments for this option are the same as the --to-source argument for the SNAT extension target.

MASQUERADE

Masquerade the packet so it appears that it originated from the current system. Reverse packets from masqueraded connections are unmasqueraded automatically. This is a legal target only for chains in the nat table that handle incoming packets and should be used only with dynamic IP addresses (like dial-up.) For static addresses use DNAT.

--to-ports port[-port]: Specify the port or range of ports to use when masquerading. This option is valid only if a tcp or udp protocol has been specified with the -p option. If this option is not used, the masqueraded packet's port will not be changed.

REDIRECT

Redirect the packet to a local port. This is useful for creating transparent proxies.

--to-ports port[-port]: Specify the port or range of ports on the local system to which the packet should be redirected. This option is valid only if a tcp or udp protocol has been specified with the -p option. If this option is not used, the redirected packet's port will not be changed.

ULOG

Userspace logging. Multicast matching packets though a netlink socket, which is a socket linking kernel space and userspace. One or more userspace processes can subscribe to the multicast groups and receive the packets.

--ulog-nlgroup n: Send packet to the specified netlink group (1-32). The default group is 1.
--ulog-prefix prefix: Prefix packet messages with the specified prefix of 32 characters or less.
--ulog-cprange n: Copy up to n bytes of the packet to the netlink socket. The default value, 0, copies an entire packet, regardless of size.
--ulog-qthreshold n: Transmit packets when n packets have been queued. Default value is 1.

TCPMSS

Alter the MSS value of TCP SYN packets.

--set-mss n: Set the MSS value to n.
--clamp-mss-to-pmtu

iptables-restore

iptables-restore [options]

System administration command. Restore firewall rules from information provided on standard input. iptables-restore takes commands generated by iptables-save and uses them to restore the firewall rules for each chain. This is often used by initialization scripts to restore firewall settings on boot.

Options

-c, --counters: Restore packet and byte counter values.
-n, --noflush: Don't delete previous table contents.

iptables-save

iptables-save [options]

System administration command. Print the IP firewall rules currently stored in the kernel to stdout. Output may be redirected to a file that can later be used by iptables-restore to restore the firewall.

Options

-c, --counters: Save packet and byte counter values.
-t name, --table name: Print data from the specified table only.

isodump

isodump isoimage

Interactively display the contents of the ISO9660 image isoimage. Used to verify the integrity of the directory inside the image. isodump displays the first portion of the root directory and waits for commands. The prompt show the extent number (zone) and offset within the extent, and the contents display at the top of the screen.

Commands

+: Search forward for the next instance of the search string.
a: Search backward within the image.
b: Search forward within the image.
f: Prompt for a new search string.
g: Prompt for a new starting block and go there.
q: Exit.

isoinfo

isoinfo [options]

Display information about ISO9660 images. You can use isoinfo to list the contents of an image, extract a file, or generate a find-like file list. The -i option is required to specify the image to examine.

Options

-d: Print information from the primary volume descriptor (PVD) of the ISO9660 image, including information about Rock Ridge and Joliet extensions if they are present.
-f: Generate output similar to the output of a find . -print command. Do not use with -l.
-h: Print help information and exit.
-i isoimage: Specify the path for the ISO9660 image to examine.
-j charset: Convert any Joliet filenames to the specified character set.
-J: Extract filename information from any Joliet extensions.
-l: Generate output similar to the output of an ls -lR command. Do not use with -f.
-N sector: To help examine single-session CD files that are to be written to a multisession CD. Specify the sector number at which the ISO9660 image is to be written when sent to the CD writer.
-p: Display path table information.
-R: Extract permission, filename, and ownership information from any Rock Ridge extensions.
-T sector: To help examine multisession images that have already been burned to a multisession CD. Use the specified sector number as the start of the session to display.
-x path: Extract the file at the specified path to standard output.

isosize

isosize [option] iso9660-img-file

Display the length of an ISO9660 filesystem contained in the specified file. The image file can be a normal file or a block device such as /dev/sr0. With no options, the length is displayed in bytes. Only one of the two options can be specified.

Options

-d num: Display the size in bytes divided by num.
-x: Display the number of blocks and the blocksize (although the output refers to blocks as sectors).

isovfy

isovfy isoimage

Verify the integrity of the specified ISO9660 image and write the results to standard output.

ispell

ispell [options] [files]

Compare the words of one or more named files with the system dictionary. Display unrecognized words at the top of the screen, accompanied by possible correct spellings, and allow editing via a series of commands.

Options

-b: Back up original file in filename.bak.
-d file: Search file instead of standard dictionary file.
-m: Suggest different root/affix combinations.
-n: Expect nroff or troff input file.
-p file: Search file instead of personal dictionary file.
-t: Expect T_EX or L^AT_EX input file.
-w chars: Consider chars to be legal, in addition to a-z and A-Z.
-x: Do not back up original file.
-B: Search for missing blanks (resulting in concatenated words) in addition to ordinary misspellings.
-C: Do not produce error messages in response to concatenated words.
-L number: Show number lines of context.
-M: List interactive commands at bottom of screen.
-N: Suppress printing of interactive commands.
-P: Do not attempt to suggest more root/affix combinations.
-S: Sort suggested replacements by likelihood that they are correct.
-T type: Expect all files to be formatted by type.
-W n: Never consider words that are n characters or fewer to be misspelled.
-V: Use hat notation (^L) to display control characters, and M- to display characters with the high bit set.

Interactive commands

?: Display help screen.
space: Accept the word in this instance.
number: Replace with suggested word that corresponds to number.
!command: Invoke shell and execute command in it. Prompt before exiting.
a: Accept word as correctly spelled, but do not add it to personal dictionary.
i: Accept word and add it (with any current capitalization) to personal dictionary.
l: Search system dictionary for words.
q: Exit without saving.
r: Replace word.
u: Accept word and add lowercase version of it to personal dictionary.
x: Skip to the next file, saving changes.
^L: Redraw screen.
^Z: Suspend ispell.

join

join [options] file1 file2

Join lines of two sorted files by matching on a common field. If either file1 or file2 is -, read from standard input.

Options

-a filenum: Print a line for each unpairable line in file filenum, in addition to the normal output.
-e string: Replace missing input fields with string.
-i, --ignore-case: Ignore case differences when comparing keys.
-1 fieldnum1: The join field in file1 is fieldnum1. Default is the first field.
-2 fieldnum2: The join field in file2 is fieldnum2. Default is the first field.
-o fieldlist: Order the output fields according to fieldlist, where each entry in the list is in the form filenum.fieldnum. Entries are separated by commas or blanks.
-t char: Specifies the field-separator character (default is whitespace).
-v filenum: Print only unpairable lines from file filenum.
--help: Print help message and then exit.
--version: Print the version number and then exit.

kbd_mode

kbd_mode [option]

Print or set the current keyboard mode, which may be RAW, MEDIUMRAW, XLATE, or UNICODE.

Options

-a: Set mode to XLATE (ASCII mode).
-k: Set mode to MEDIUMRAW (keycode mode).
-s: Set mode to RAW (scancode mode).
-u: Set mode to UNICODE (UTF-8 mode).

kbdrate

kbdrate [options]

System administration command. Control the rate at which the keyboard repeats characters, as well as its delay time. Using this command without options sets a repeat rate of 10.9 characters per second; the default delay is 250 milliseconds. When Linux boots, however, it sets the keyboard rate to 30 characters per second.

Options

-s: Suppress printing of messages.
-r rate: Specify the repeat rate, which must be one of the following numbers (all in characters per second): 2.0, 2.1, 2.3, 2.5, 2.7, 3.0, 3.3, 3.7, 4.0, 4.3, 4.6, 5.0, 5.5, 6.0, 6.7, 7.5, 8.0, 8.6, 9.2, 10.0, 10.9, 12.0, 13.3, 15.0, 16.0, 17.1, 18.5, 20.0, 21.8, 24.0, 26.7, or 30.0.
-d delay: Specify the delay, which must be one of the following (in milliseconds): 250, 500, 750, or 1000.

kernelversion

kernelversion

This command tells you what version of the Linux kernel you are using. It is also used by modultils and the /etc/modules.conf file to determine where to put kernel modules. It accepts no arguments or options.

kill

kill [options] [pids | commands]

Send a signal to terminate one or more process IDs. You must own the process or be a privileged user. If no signal is specified, TERM is sent.

This entry describes the /bin/kill command, which offers several powerful features. There are also built-in shell commands of the same name; the bash version is described in Chapter 7 and the tcsh version in Chapter 8.

In particular, /bin/kill allows you to specify a command name, such as gcc or xpdf, instead of a process ID (PID). All processes running that command with the same UID as the process issuing /bin/kill will be sent the signal.

If /bin/kill is issued with a pid of 0, it sends the signal to all processes of its own process group. If /bin/kill is issued with a pid of -1, it sends the signal to all processes except process 1 (the system's init process).

Options

-a: Kill all processes of the given name (if privileges allow), not just processes with the same UID. To use this option, specify the full path (e.g., /bin/kill -a gcc).
-l: List all signals.
-p: Print the process ID of the named process, but don't send it a signal. To use this option, specify the full path (e.g., /bin/kill -p).
-signal: The signal number (from /usr/include/sys/signal.h) or name (from kill -l). With a signal number of 9 (HUP), the kill cannot be caught by the process; use this to kill a process that a plain kill doesn't terminate. The default is TERM.

killall

killall [options] names

Kill processes by command name. If more than one process is running the specified command, kill all of them. Treat command names that contain a / as files; kill all processes that are executing that file.

Options

-signal: Send signal to process (default is TERM). signal may be a name or a number.
-e: Require an exact match to kill very long names (i.e., longer than 15 characters). Normally, killall kills everything that matches within the first 15 characters. With -e, such entries are skipped. (Use -v to print a message for each skipped entry.)
-g: Kill the process group to which the process belongs.
-i: Prompt for confirmation before killing processes.
-l: List known signal names.
-q: Quiet; do not complain of processes not killed.
-v: Verbose; after killing process, report success and process ID.
-V: Print version information.
-w: Wait for all killed processes to die. Note that killall may wait forever if the signal was ignored or had no effect, or if the process stays in zombie state.

killall5

killall5

The System V equivalent of killall, this command kills all processes except those on which it depends.

klogd

klogd [options]

System administration command. Control which kernel messages are displayed on the console, prioritize all messages, and log them through syslogd. On many operating systems, syslogd performs all the work of klogd, but on Linux the features are separated. Kernel messages are gleaned from the /proc filesystem and from system calls to syslogd. By default, no messages appear on the console. Messages are sorted into eight levels, 0-7, and the level number is prepended to each message.

Priority levels

0: Emergency situation (KERN_EMERG).
1: A crucial error has occurred (KERN_ALERT).
2: A serious error has occurred (KERN_CRIT).
3: An error has occurred (KERN_ERR).
4: A warning message (KERN_WARNING).
5: The situation is normal but should be checked (KERN_NOTICE).
6: Information only (KERN_INFO).
7: Debugging messages (KERN_DEBUG).

Options

-c level: Print all messages of a higher priority (lower number) than level to the console.
-d: Debugging mode.
-f file: Print all messages to file; suppress normal logging.
-i: Signal executing daemon to reload kernel module symbols.
-k file: Use file as source of kernel symbols.
-n: Avoid auto-backgrounding. This is needed when klogd is started from init.
-o: One-shot mode. Prioritize and log all current messages, then immediately exit.
-p: Reload kernel module symbol information whenever an Oops string is detected.
-s: Suppress reading of messages from the /proc filesystem. Read from kernel message buffers instead.
-v: Print version, then exit.
-x: Don't translate instruction pointers (EIP). klogd will not read the System.map file.
-I: Signal executing daemon to reload both static kernel symbols and kernel module symbols.
-2: Print two lines for each symbol, one showing the symbol and the other showing its numerical value (address).

Files

/usr/include/linux/kernel.h, /usr/include/sys/syslog.h: Sources for definitions of each logging level.
/proc/kmsg: A file examined by klogd for messages.
/var/run/klogd.pid: klogd's process ID.

ksyms

ksyms [options]

System administration command. Print a list of all exported kernel symbols (name, address, and defining module, if applicable).

Options

-a, --all: Include symbols from unloaded modules.
-h, --noheader: Suppress header message.
-m, --info: Include starting address and size. Useful only for symbols in loaded modules.
-H, --help: Print help message, then exit.
-V, --version: Print version, then exit.

File

/proc/ksyms: Another source of the same information.

last

last [options] [username] [ttynumber]

Display a list of the most recent logins, taken from the file /var/log/wtmp by default. If you specify a tty number or username, the output will display only the logins for that user or terminal.

Options

-n number, -number: Choose how many lines of logins to display. Thus, last -7 or last -n 7 displays seven lines.
-R: Do not show the hostname from which logins originated.
-a: Display the hostname from which logins originated.
-d: Display both IP address and hostname.
-f filename: Get the list of logins from a file you choose. The default source is /var/log/wtmp.
-i: Display IP address and hostname. Display the IP address in the numbers-and-dots notation.
-o: Read an old-style (libc5 application) wtmp file. Not likely to be useful on newer systems.
-x: Display shutdown messages and runlevel messages.

lastb

lastb [options] [username] [ttynumber]

Display a list of recent bad login attempts (from the /var/log/btmp file). Accepts the same option flags and arguments as last.

lastlog

lastlog [options]

System administration command. Print the last login times for system accounts. Login information is read from the file /var/log/lastlog.

Options

-tn: Print only logins more recent than n days ago.
-uname: Print only login information for user name.

ld [options] objfiles

Combine several objfiles, in the specified order, into a single executable object module (a.out by default). ld is the link editor and is often invoked automatically by compiler commands. ld accepts many options, the most common of which are listed here.

Options

-b format, --format=format

If ld is configured to accept more than one kind of object file, this command can be used to specify the input format. format should be a GNU Binary File Descriptor (BFD) as described in the BFD library. Use objdump -i to list available formats.

-call_shared

Link with dynamic libraries.

-d, -dc, -dp

Force the assignment of space to common symbols.

-defsym symbol=expression

Create the global symbol with the value expression.

-demangle[=style]

Force demangling of symbol names. Optionally set the demangling style. Turn off demangling with -nodemangle.

-e symbol

Set symbol as the address of the output file's entry point.

-f name

Set the DT_AUXILIARY field of ELF shared object to name.

-fini name

Set the DT_FINI field of ELF shared object to the address of function name. The default function is _fini.

-h name

Set the DT_SONAME field of ELF shared object to name.

--help

Produce a linkable output file; attempt to set its magic number to OMAGIC.

-i

-init name

Set the DT_INIT field of ELF shared object to the address of function name. The default function is _init.

-larch, --library=archive

Include the archive file arch in the list of files to link.

-m linker

Emulate linker. List supported emulations with the -V option.

-n

Make text read-only; attempt to set NMAGIC.

-o output

Place output in output, instead of a.out.

-oformat format

Specify output format.

-q

Retain relocation sections and contents in linked executables.

-r

Produce a linkable output file; attempt to set its magic number to OMAGIC.

-rpath dir

Add directory dir to the runtime library search path. Ignore additional paths normally read from the LD_RUN_PATH environment variable.

-rpath-link dirs

Specify path to search for shared libraries required by another shared library. The dirs argument can be a single directory, or multiple directories separated by colons. This overrides search paths specified in shared libraries themselves.

-s

Do not include any symbol information in output.

-shared

Create a shared library.

-static

Do not link with shared libraries.

-sort-common

Do not sort global common symbols by size.

-t

Print each input file's name as it is processed.

--target-help

Print target-specific options, then exit.

-u symbol

Force symbol to be undefined.

-v, --version

Show version number.

--verbose

Print information about ld; print the names of input files while attempting to open them.

-warn-common

Warn when encountering common symbols combined with other constructs.

-warn-once

Provide only one warning per undefined symbol.

-x

With -s or -S, delete all local symbols. These generally begin with L.

-z keyword

Mark the object for special behavior specified by keyword. ld recognizes the following keywords:

combreloc: Object combines and sorts multiple relocation sections for dynamic symbol lookup caching.
defs: Disallow undefined symbols.
initfirst: Initialize object first at runtime.
interpose: Interpose object's symbol table before all but the primary executable's symbol table.
loadfltr: Process object's filter immediately at runtime.
multidefs: Allow multiple definitions of a single symbol. Use the first definition.
nocombreloc: Disable combining multiple relocation sections.
nocopyreloc: Disable copy relocation.
nodefaultlib: Ignore default library search path when seeking dependencies for object.
nodelete: Do not unload object at runtime.
nodlopen: Object is not available to dlopen.
nodump: Object cannot be dumped by dldump.
now: Non-lazy runtime binding.
origin: Object may contain $ORIGIN.

-E, --export-dynamic

Add all symbols to dynamic symbol table, not just those referenced by linked objects.

-EB

Link big-endian objects.

-EL

Link little-endian objects.

-F name

Set DT_FILTER field of ELF shared object to name.

-Ldir, --library-path=dir

Search directory dir before standard search directories (this option must precede the -l option that searches that directory).

-M

Display a link map on standard output.

-Map file

Print a link map to file.

-N

Allow reading of and writing to both data and text. Mark ouput if it supports Unix magic numbers. Do not page-align data.

-O level

Optimize. level should be 1, 2, 3, or 0. The default is 1. 0 turns off optimization; 3 optimizes the most.

-R file

Obtain symbol names and addresses from file, but suppress relocation of file and its inclusion in output.

-S

Do not include debugger symbol information in output.

-T file

Execute script file instead of the default linker script.

-Tbss address

Begin bss segment of output at address.

-Tdata address

Begin data segment of output at address.

-Ttext address

Begin text segment of output at address.

-Ur

Synonymous with -r except when linking C++ programs, where it resolves constructor references.

-X

With -s or -S, delete local symbols beginning with L.

-V

Show version number and emulation linkers for -m option.

ldconfig

ldconfig [options] directories

System administration command. Examine the libraries in the given directories, /etc/ld.so.conf, /usr/lib, and /lib; update links and cache where necessary. Usually run in startup files or after the installation of new shared libraries.

Options

-D: Debug mode. Suppress all normal operations.
-l: Library mode. Expect libraries as arguments, not directories. Manually link specified libraries.
-n: Suppress examination of /usr/lib and /lib and reading of /etc/ld.so.conf; do not cache.
-N: Do not cache; only link.
-p: Print all directories and candidate libraries in the cache. Used without arguments.
-v: Verbose mode. Include version number, and announce each directory as it is scanned and links as they are created.
-X: Do not link; only rebuild cache.

Files

/lib/ld.so: Linker and loader.
/etc/ld.so.conf: List of directories that contain libraries.
/etc/ld.so.cache: List of the libraries found in those libraries mentioned in /etc/ld.so.conf.

ldd

ldd [options] programs

Display a list of the shared libraries each program requires.

Options

-d, --data-relocs: Process data relocations. Report missing objects.
-r, --function-relocs: Process relocations for both data objects and functions. Report any that are missing.
-v, --verbose: Display ldd's version.
--help: Print help message, then exit.
--version: Display the linker's version, then exit.

less

less [options] [filename]

less is a program for paging through files or other output. It was written in reaction to the perceived primitiveness of more (hence its name). Some commands may be preceded by a number.

Options

-[z]num, --window=num: Set number of lines to scroll to num. Default is one screenful. A negative num sets the number to num lines less than the current number.
+[+]command: Run command on startup. If command is a number, jump to that line. The option ++ applies this command to each file in the command-line list.
-?, --help: Print help screen. Ignore all other options; do not page through file.
-a, --search-screen: When searching, begin after last line displayed. (Default is to search from second line displayed.)
-bbuffers, -buffers=buffers: Use buffers buffers for each file (default is 10). Buffers are 1 KB in size.
-c, --clear-screen: Redraw screen from top, not bottom.
-d, --dumb: Suppress dumb-terminal error messages.
-e, --quit-at-eof: Automatically exit after reaching EOF twice.
-f, --force: Force opening of directories and devices; do not print warning when opening binaries.
-g, --hilite-search: Highlight only string found by past search command, not all matching strings.
-hnum, --max-back-scroll=num: Never scroll backward more than num lines at once.
-i, --ignore-case: Make searches case-insensitive, unless the search string contains uppercase letters.
-jnum, --jump-target=num: Position target line on line num of screen. Target line can be the result of a search or a jump. Count lines beginning from 1 (top line). A negative num is counted back from bottom of screen.
-kfile, --lesskey-file=file: Read file to define special key bindings.
-m, --long-prompt: Display more-like prompt, including percent of file read.
-n, --line-numbers: Do not calculate line numbers. Affects -m and -M options and = and v commands (disables passing of line number to editor).
-ofile, --log-file=file: When input is from a pipe, copy output to file as well as to screen. (Prompt for overwrite authority if file exists.)
-ppattern, --pattern=pattern: At startup, search for first occurrence of pattern.
-q, --quiet, --silent: Disable ringing of bell on attempts to scroll past EOF or before beginning of file. Attempt to use visual bell instead.
-r, --raw-control-chars: Display "raw" control characters instead of using ^x notation. This sometimes leads to display problems, which might be fixed by using -R instead.
-s, --squeeze-blank-lines: Print successive blank lines as one line.
-ttag, --tag=tag: Edit file containing tag. Consult ./tags (constructed by ctags).
-u, --underline-special: Treat backspaces and carriage returns as printable input.
-w, --hilite-unread: Show the line to which a movement command has skipped, phrases displayed by a search command, or the first unread line during a normal scroll by highlighting text in reverse video.
-xn, --tabs=n: Set tab stops to every n characters. Default is 8.
-yn, --max-forw-scroll=n: Never scroll forward more than n lines at once.
-B, --auto-buffers: Do not automatically allocate buffers for data read from a pipe. If -b specifies a number of buffers, allocate that many. If necessary, allow information from previous screens to be lost.
-C, -CLEAR-SCREEN: Redraw screen by clearing it and then redrawing from top.
-E, --QUIT-AT-EOF: Automatically exit after reaching EOF once.
-F, --quit-if-one-screen: Exit without displaying anything if first file can fit on a single screen.
-G, --HILITE-SEARCH: Never highlight matching search strings.
-I, --IGNORE-CASE: Make searches case-insensitive, even when the search string contains uppercase letters.
-J, --status-column: Used with -w or -W, highlight a single column on the left edge of the screen instead of the whole text of an unread line.
-Kcharset: Use the specified charset.
-M: Prompt more verbosely than with -m, including percentage, line number, and total lines.
-N, --LINE-NUMBERS: Print line number before each line.
-Ofile, --LOG-FILE=file: Similar to -o, but do not prompt when overwriting file.
-P[mM=]prompt: Set the prompt displayed by less at the bottom of each screen to prompt. The m sets the prompt invoked by the -m option, the M sets the prompt invoked by the -M option, and the = sets the prompt invoked by the = command. Special characters (described in the manpage for less), can be used to print statistics and other information in these prompts.
-Q, --QUIET, --SILENT: Never ring terminal bell.
-R, --RAW-CONTROL-CHARS: Like r, but adjust screen to account for presence of control characters.
-S, --chop-long-lines: Cut, do not fold, long lines.
-Tfile, --tag-file=file: With the -t option or :t command, read file instead of ./tags.
-U, --UNDERLINE-SPECIAL: Treat backspaces and carriage returns as control characters.
-V, --version: Display version and exit.
-W, --HILITE-UNREAD: Show phrases displayed by a search command, or the first unread line of any forward movement that is more than one line, by highlighting text in reverse video.
-X, --no-init

Commands

Many commands can be preceded by a numeric argument, referred to as number in the command descriptions.

SPACE, ^V, f, ^F

Scroll forward the default number of lines (usually one windowful).

RETURN, ^N, e, ^E, j, ^J

Scroll forward. Default is one line. Display all lines, even if the default is more lines than the screen size.

d, ^D

Scroll forward. Default is one-half the screen size. The number of lines may be specified, in which case the default is reset.

b, ^B, ESC-v

Scroll backward. Default is one windowful.

Like b, but allows the number of lines to be specified, in which case it resets the default to that number.

y, ^Y, ^P, k, ^K

Scroll backward. Default is one line. Display all lines, even if the default is more lines than the screen size.

u, ^U

Scroll backward. Default is one-half the screen size. The number of lines may be specified, in which case the default is reset.

r, ^R, ^L

Redraw screen.

Like r, but discard buffered input.

Scroll forward. When an EOF is reached, continue trying to find more output, behaving similarly to tail -f.

g, <, ESC-<

Skip to a line. Default is 1.

G, >, ESC->

Skip to a line. Default is the last one.

p, %

Skip to a position number percent of the way into the file.

{

If the top line on the screen includes a {, find its matching }. If the top line contains multiple {s, use number to determine which one to use in finding a match.

}

If the bottom line on the screen includes a }, find its matching {. If the bottom line contains multiple }s, use number to determine which one to use in finding a match.

(

If the top line on the screen includes a (, find its matching ). If the top line contains multiple (s, use number to determine which one to use in finding a match.

)

If the bottom line on the screen includes a ), find its matching (. If the bottom line contains multiple )s, use number to determine which one to use in finding a match.

[

If the top line on the screen includes a [, find its matching ]. If the top line contains multiple [s, use number to determine which one to use in finding a match.

]

If the bottom line on the screen includes a ], find its matching [. If the bottom line contains multiple ]s, use number to determine which one to use in finding a match.

ESC-^F

Behave like { but prompt for two characters, which it substitutes for { and } in its search.

ESC-^B

Behave like } but prompt for two characters, which it substitutes for { and } in its search.

Prompt for a lowercase letter and then use that letter to mark the current position.

Prompt for a lowercase letter and then go to the position marked by that letter. There are some special characters:

^: Beginning of file.
$: End of file.

^X^X

Same as '.

/pattern

Find next occurrence of pattern, starting at second line displayed. Some special characters can be entered before pattern:

!: Find lines that do not contain pattern.
*: If current file does not contain pattern, continue through the rest of the files in the command-line list.
@: Search from the first line in the first file specified on the command line, no matter what the screen currently displays.

?pattern

Search backward, beginning at the line before the top line. Treats !, *, and @ as special characters when they begin pattern, as / does.

ESC-/pattern

Same as /*.

ESC-?pattern

Same as ?*.

Repeat last pattern search.

Repeat last pattern search in the reverse direction.

ESC-n

Repeat previous search command but as though it were prefaced by *.

ESC-N

Repeat previous search command but as though it were prefaced by * and in the reverse direction.

ESC-u

Toggle search highlighting.

:e [filename]

Read in filename and insert it into the command-line list of filenames. Without filename, reread the current file. filename may contain special characters:

%: Name of current file
#: Name of previous file

^X^V, E

Same as :e.

Read in next file in command-line list.

Read in previous file in command-line list.

Read in first file in command-line list.

:f, =, ^G

Print filename, position in command-line list, line number on top of window, total lines, byte number, and total bytes.

Expects to be followed by a command-line option letter. Toggle the value of that option or, if appropriate, prompt for its new value.

Expects to be followed by a command-line option letter. Reset that option to its default.

Expects to be followed by a command-line option letter. Reset that option to the opposite of its default, where the opposite can be determined.

Expects to be followed by a command-line option letter. Display that option's current setting.

+command

Execute command each time a new file is read in.

q, :q, :Q, ZZ

Exit.

Not valid for all versions. Invoke editor specified by $VISUAL or $EDITOR, or vi if neither is set.

! [command]

Not valid for all versions. Invoke $SHELL or sh. If command is given, run it and then exit. Special characters:

%: Name of current file.
#: Name of previous file.
!!: Last shell command.

| mark-letter command

Not valid for all versions. Pipe fragment of file (from first line on screen to mark-letter) to command. mark-letter may also be:

^: Beginning of file.
$: End of file.
., newline

Prompts

The prompt interprets certain sequences specially. Those beginning with % are always evaluated. Those beginning with ? are evaluated if certain conditions are true. Some prompts determine the position of particular lines on the screen. These sequences require that a method of determining that line be specified. See the -P option and the manpage for more information.

lesskey

lesskey [-o output-file | --output=output-file] [input-file]

Configure keybindings for the less command using a configuration file. The input file defaults to ~/.lesskey and the output file to ~/.less unless you specify otherwise.

Configuration file format

The configuration file for lesskey has one to three sections. These are marked by a line containing a # symbol and the name of the section: #command, #line-edit, and #env.

The #command section

The command section determines the keys used for actions within less. Each line should contain the key or key combination you wish to define, a space or tab, and the name of the action to perform. You may also add an extra string at the end, which will be performed at the end of the first action.

Keys you define should be entered as you plan to type them, with the exception of the caret (^), space, tab, and backslash (\) characters, which should be preceded by a backslash. In addition, the following special keys are represented by escape sequences that begin with a backslash:

Backspace: \b
Escape: \e
Newline: \n
Return: \r
Tab: \t
Up arrow: \ku
Down arrow: \kd
Right arrow: \kr
Left arrow: \kl
Page up: \kU
Page down: \kD
Home: \kh
End: \ke
Delete: \kx

The actions that can be defined are:

invalid (creates error)
noaction
forw-line
back-line
forw-line-force
forw-scroll
back-scroll
forw-screen
back-screen
forw-window
back-window
forw-screen-force
forw-forever
repaint-flush
repaint
undo-hilite
goto-line
percent
left-scroll
right-scroll
forw-bracket
back-bracket
goto-end
status
forw-search
back-search
repeat-search
repeat-search-all
set-mark
goto-mark
examine
next-file
index-file
prev-file
toggle-option
display-option
pipe
visual
shell
firstcmd
help
version (display version)
digit (display number)
quit

The #line-edit section

The line editing section lets you choose keys for the line-editing capabilities of less in a similar manner to the #command section, although without the "extra" string after the command. The line editing actions that can be defined are:

forw-complete
back-complete
expand
literal
right
left
word-left
word-right
insert
delete
word-delete
word-backspace
home
end
up
down

The #env section

The third section, like the second, is optional, and you can use it to override environment variables that affect less. Each line consists of a variable, the equals sign (=), and the value to which you wish to set the variable. The most important ones are LESS, which allows you to select additional flags to pass to less when you run it, and LESSCHARSET, which lets you choose a character set. Check the less manpage for a complete list of environment variables that affect the program.

lftp

lftp [options] [url]

File transfer program with more features than ftp. The lftp command allows FTP and HTTP protocol transfers, plus other protocols including FISH (SSH based), FTPS, and HTTPS. It uses a shell-like command interface and offers job control in a manner similar to bash. lftp has two important reliability features: it resumes failed or interrupted transactions, and it goes into the background automatically if it is quit in the middle of a file transfer.

Options

-d: Run in debug mode.
-e commands: Start, execute the specified commands, and then wait for further instructions.
-p portnumber: Connect to the specified port number.
-u user[,pass]: Login to the server with the username (and, optionally, password) you specify.
-f scriptfile: Run the specified script file of lftp commands, then exit.
-c commands: Run the commands specified, then exit.

Commands

The lftp commands are similar to those for ftp. However, lftp lacks or uses different mechanisms for a number of commands, including $, ascii, binary, case, and macdef. It also adds the following:

alias [name [value]]

Create an alias for a command. For example, you could set dir to be an alias for ls -lf.

anon

Set the username to anonymous. This is the default username.

at

Execute a command at a given time, as with the at command in an actual shell.

bookmark [arguments]

The lftp bookmark command used with the following arguments will add, delete, edit, import, or list bookmarks, respectively:

add name url
del name
edit
import type
list

cache

Work with the local memory cache. This command should be followed by the arguments:

stat: Display the status for the cache.
on|off: Turn caching on or off.
flush: Empty the cache.
size n: Set the maximum size for the cache. Setting it to -1 means unlimited.
expire nu: Set the cache to expire after n units of time. You can set the unit to seconds (s), minutes (m), hours (h), or days (d). For example, for a cache that expires after an hour, use the syntax cache expire 1h.

close

Where the ftp version of this command just stops all sessions, this version closes idle connections with the current server. If you have connections to multiple servers and wish to close all idle connections, add the -a flag.

command cmd args

Execute the specified lftp command, with the specified arguments, ignoring any aliases created with the alias command.

mirror [options] [remotedir [localdir]]

Copy a directory exactly. The mirror command accepts the following arguments:

-c, --continue: If mirroring was interrupted, resume it.
-e, --delete: Delete local files that are not present at the remote site.
-s, --allow-suid: Keep the suid/sgid bits as set on the remote site.
-n, --only-newer: Get only those files from the remote site that have more recent dates than the files on the local system. Cannot be used with the -c argument.
-r, --no-recursion: Do not get any subdirectories.
--no-umask: Do not use umask when getting file modes. See umask for more information about file modes.
-R, --reverse: Mirror files from the local system to the remote system. With this argument, make sure that you specify the local directory first and the remote directory second. If you do not specify both directories, the second is assumed to be the same as the first. If you choose neither, the operation occurs in the current working directories.
-L, --dereference: When mirroring a link, download the file the link points to rather than just the link.
-N, --newer-than filename: Get all files newer than the file filename.
-P, --parallel[=n]: Download n files in parallel.
-i, --include regex: Get only the files whose names match the regular expression regex. See grep for more information about regular expressions.
-x, --exclude regex: Do not get the files whose names match regex. See grep for more information about regular expressions.
-t, time-prec n: Set the precision of time measurement for file comparison; if file dates differ by amounts less than n, they are assumed to be the same. You can specify n in seconds (s), minutes (m), hours (h), or days (d).
-T, --loose-time-prec n: Set the precision for loose time comparisons. You can specify n in seconds (s), minutes (m), hours (h), or days (d).
-v, --verbose=n: Set the verbose level. You can set n from 0 (no output) to 3 (full output) using a number or by repeating the v. For example, -vvv is level 3 verbose mode.
--use-cache: Use the cache to get directory listings.
--remove-source-files: Move, rather than copy, files when mirroring.

set [setting | value]

Set one of the preference variables for lftp. If run without arguments, list the variables that have been changed; without arguments and with the -a or -d flags, list all values or default values, respectively.

See the lftp manpage for a complete list of preference variables that can be set.

wait [n | all]

lftpget

lftpget [options] url

Uses the lftp program to fetch the specified URL, which may be HTTP, FTP, or any of the protocols supported by lftp.

Options

lftpget takes only three options:

-c: Continue or restart a paused transaction.
-d: Display debugging output.
-v: Verbose mode; display more information about transactions.

link

link file1 file2

Create a link between two files. This is the same as the ln command, but it has no error checking because it uses the link( ) system call directly.

ln [options] sourcename [destname]
ln [options] sourcenames destdirectory

Create pseudonyms (links) for files, allowing them to be accessed by different names. The first form links sourcename to destname, where destname is usually either a new filename or (by default) a file in the current directory with the same name as sourcename. If destname is an existing file, it is overwritten; if destname is an existing directory, a link named sourcename is created in that directory. The second form creates links in destdirectory, each link having the same name as the file specified.

Options

-b, --backup=[control]

Back up any existing files. When using the long version of the command, the optional control parameter controls the kind of backup. When no control is specified, ln will attempt to read the control value from the VERSION_CONTROL environment variable. Accepted values are:

none, off: Never make backups.
numbered, t: Make numbered backups.
existing, nil: Match existing backups, numbered or simple.
simple, never: Always make simple backups.

-d, -F, --directory

Allow hard links to directories. Available to privileged users.

-f, --force

Force the link (don't prompt for overwrite permission).

--help

Prompt for permission before removing files.

-i, --interactive

-n, --no-dereference

Replace symbolic links to directories instead of dereferencing them. --force is useful with this option.

-s, --symbolic

Create a symbolic link. This lets you link across filesystems, and also see the name of the link when you run ls -l (otherwise, there's no way to know the name that a file is linked to).

-S suffix, --suffix=suffix

Append suffix to files when making backups, instead of the default ~.

--target-directory= diectory

Create links in the specified diectory.

-v, --verbose

--version

List summary of commands (help screen).

loadkeys

loadkeys [options] [filename]

Load a keymap from a specified file, usually one of the keymaps stored in /lib/kbd/keymaps. If you create your own keymap file, the related commands showkey, keymaps, and dumpkeys will be useful as well.

Options

-c, --clearcompose: Clear the compose, or accent, table in the kernel.
-d, --default: Load the default keymap. The same as running loadkeys defkeymap.
-h, --help: Display help and usage information.
-m, --mktable: Instead of loading the table, output maps as C language declarations.
-q, --quiet: Operate in quiet mode.
-s, --clearstrings: Clear the string table in the kernel.
-v, --verbose: Operate verbosely. For extra effect, repeat.

locale

locale [options] [name]

Print report on current locale settings. Locales determine the country-specific settings for a system, including character encodings, the formatting of dates, honorifics, diagnostic messages, currency, printer paper sizes, and default measurements. Locale settings are essentially a dictionary of settings specified by keyword. The keywords are grouped together into related categories whose names begin with LC_. Each category has a related environment variable of the same name from which it will read its locale setting. Supply keyword or category names as name to examine their values. Multiple names may be given. You can also use the special keyword charmap to see the current character mapping. When executed with no arguments, locale prints the value of all locale-related environment variables.

Options

-a: Print all available locale settings installed on the system.
-c: Print the category related to each name argument.
-k: Print keywords along with their settings for each name argument.
-m: Print all available character maps.

Environment variables

LANG: The default value for unset internationalization variables. If not set, the system's default value is used.
LC_ADDRESS: Postal settings, country, and language names and abbreviation.
LC_COLLATE: String and character sorting and comparison settings.
LC_CTYPE: Character attributes, including case conversion mappings, and categories of characters (whitespace, digit, lower, upper, punctuation, etc.).
LC_IDENTIFICATION: Information related to the current locale definition, including its title, source, revision, and contact information for its author.
LC_MEASUREMENT: Measurement units, metric or other.
LC_MESSAGES: Settings for yes/no prompts and other informative and diagnostic messages.
LC_MONETARY: Currency formats and symbols.
LC_NAME: Formats for names and honorifics.
LC_NUMERIC: Non-monetary number formats.
LC_PAPER: Default paper sizes for printing and pagination.
LC_TELEPHONE: Telephone number formats.
LC_TIME: Date and time formats.
LC_ALL: When set, overrides the values of all other internationalization variables.
NLSPATH: The path for finding message catalogues used in processing messages.

Examples

Print the category name and all keywords for date and time settings:

locale -ck LC_TIME

Print the strings used for days of the week and months of the year:

locale day mon

locate

locate [options] pattern

Search database(s) of filenames and print matches. *, ?, [, and ] are treated specially; / and . are not. Matches include all files that contain pattern unless pattern includes metacharacters, in which case locate requires an exact match.

Options

-d path, --database=path: Search databases in path. path must be a colon-separated list.
-h, --help: Print a help message and then exit.
--version: Print version information and then exit.

lockfile

lockfile [options] filenames

Create semaphore file(s), used to limit access to a file. When lockfile fails to create some of the specified files, it pauses for 8 seconds and retries the last one on which it failed. The command processes flags as they are encountered (i.e., a flag that is specified after a file will not affect that file).

Options

-sleeptime: Number of seconds lockfile waits before retrying after a failed creation attempt. Default is 8.
-!: Invert return value. Useful in shell scripts.
-l lockout_time: Time (in seconds) after a lockfile was last modified at which it will be removed by force. See also -s.
-ml, -mu: If the permissions on the system mail spool directory allow it or if lockfile is suitably setgid, lockfile can lock and unlock your system mailbox with the options -ml and -mu, respectively.
-r retries: Stop trying to create files after retries retries. The default is -1 (never stop trying). When giving up, remove all created files.
-s suspend_time: After a lockfile has been removed by force (see -l), a suspension of 16 seconds takes place by default. (This is intended to prevent the inadvertent immediate removal of any lockfile newly created by another program.) Use -s to change the default 16 seconds.

logger

logger [options] [message...]

TCP/IP command. Add entries to the system log (via syslogd). If no message is given on the command line, standard input is logged.

Options

-d: When writing to a socket with -s, use a datagram instead of a stream.
-f file: Read message from file.
-i: Include the process ID of the logger process.
-p pri: Enter message with the specified priority pri. Default is user.notice.
-s: Log message to standard error as well as to the system log.
-t tag: Mark every line in the log with the specified tag.
-u socket: Write log to socket instead of to the syslog.
-: Accept no futher options. Consider whatever is to the right of the hyphen as the message to be logged.

login

login [name | option]

Log into the system. login asks for a username (name can be supplied on the command line) and password (if appropriate).

If successful, login updates accounting files, sets various environment variables, notifies users if they have mail, and executes startup shell files.

Only the root user can log in when /etc/nologin exists. That file is displayed before the connection is terminated. Furthermore, root may connect only on a tty that is listed in /etc/securetty. If ~/.hushlogin exists, execute a quiet login. If /var/adm/lastlog exists, print the time of the last login.

Options

-f: Suppress second login authentication.
-h host: Specify name of remote host. Normally used by servers, not humans; may be used only by root.
-p: Preserve previous environment.

logname

logname [option]

Consult /var/run/utmp for user's login name. If found, print it; otherwise, exit with an error message.

Options

--help: Print a help message and then exit.
--version: Print version information and then exit.

logrotate

logrotate [options] config_files

System administration command. Manipulate log files according to commands given in config_files.

Options

-d, --debug: Debug mode. No changes will be made to log files.
-f, --force: Force rotation of log files.
-h, --help: Describe options.
-m command, --mail command: Use the specified command to mail log files. The default is /bin/mail -s.
-s file, --state file: Save state information in file. The default is /var/lib/logrotate.status.
--usage: Show syntax and options.
-v, --verbose: Describe what is being done and what log files are affected.

Commands

compress: Compress old versions of log files with gzip.
compresscmd command: Use command to compress log files. Default is gzip.
compressext extension: Append filename extension to compressed files instead of the compress command's default.
compressoptions options: Specify options to pass to the compress command. Default for gzip is -9 for maximum compression.
copy: Copy log file, but do not change the original.
copytruncate: Copy log file, then truncate it in place. For use with programs whose logging cannot be temporarily halted.
create [permissions] [owner] [group]: After rotation, re-create log file with the specified permissions, owner, and group. permissions must be in octal. If any of these parameters is missing, the log file's original attributes will be used.
daily: Rotate log files every day.
delaycompress: Don't compress log file until the next rotation.
endscript: End a postrotate or prerotate script.
extension extension: Give rotated log files the specified extension. Any compression extension will be appended to this.
ifempty: Rotate log file even if it is empty. Overrides the default notifempty option.
include file: Read the file into current file. If file is a directory, read all files in that directory into the current file.
mail address: Mail any deleted logs to address.
mailfirst: When using the mail command, mail the newly rotated log instead of the one being deleted.
maillast: When using the mail command, mail the log that is about to expire. This is the default behavior.
missingok: Skip missing log files. Do not generate an error.
monthly: Rotate log files only the first time logrotate is run in a month.
nocompress: Override compress.
nocopy: Override copy.
nocopytruncate: Override copytruncate.
nocreate: Override create.
nodelaycompress: Override delaycompress.
nomail: Override mail.
nomissingok: Override missingok.
noolddir: Override olddir.
nosharedscipts: Override sharedscripts. Run prerotate and postrotate scripts for each log rotated. This is the default.
notifempty: Override ifempty.
olddir directory: Move logs into directory for rotation. directory must be on the same physical device as the original log files.
postrotate: Begin a script of directives to apply after the log file is rotated. The script ends when the endscript directive is read.
prerotate: Begin a script of directives to apply before a log file is rotated. The script ends when the endscript directive is read.
rotate number: The number of times to rotate a log file before removing it.
size n[k|M]: Rotate log file when it is greater than n bytes. n can optionally be followed by k for kilobytes or M for megabytes.
sharedscripts: Run prescript and postscript only once for the session.
start n: Use n as the starting number for rotated logs. Default is 0.
tabooext [+] extlist: Replace taboo extension list with the given extlist. If + is specified, add to existing list. The default list is .rpmorig .rpmsave ,v .swp .rpmnew ~.
weekly: Rotate log files if more than a week has passed since their last rotation.
uncompresscmd command

look

look [options] string [file]

Search for lines in file (/usr/dict/words by default) that begin with string.

Options

-a: Use alternate dictionary /usr/dict/web2.
-d: Compare only alphanumeric characters.
-f: Search is not case-sensitive.
-t character: Stop checking after the first occurrence of character.

losetup

losetup [options] loopdevice [file]

System administration command. Set up and control loop devices. Attach a loop device to a regular file or block device, detach a loop device, or query a loop device. A loop device can be used to mount an image file as if it were a normal device.

Options

-d: Detach specified loopdevice.
-e encryption: Use specified encryption when performing writes and reads. Accepted values are NONE, DES, and XOR. When using DES encryption, you will be prompted for initialization values.
-o offset: Start reading data at offset bytes from the beginning of file.

lpc

lpc [options] [command]

System administration command. LPRng line printer control program. If executed without a command, lpc accepts commands from standard input. Some of the commands accept a jobid parameter. A jobid can be one or more job numbers, user names, lpd key characters, or key character and glob patterns of the form X=pattern. It can also be the keyword all, which matches all jobs.

Options

-a: Alias for the -Pall command. Operate on all printer spool queues listed in the printcap all field.
-A: Use authentication as specified in the AUTH environment variable.
-Pprinter: Specify the print spool queue to operate on. A printer may also specify a host (e.g., printer@host). The default queue is the queue for whatever printer is listed in the PRINTER environment variable, or the first entry in the /etc/printcap file. If the keyword all is given instead of a printer name, lpc will operate on printers specified in the all field of the /etc/printcap file on the appropriate host. If no all field is specified, then lpc will use lpd on the appropriate host to find all available printers.
-Sserver: Send commands to the specified server instead of whatever server is listed in /etc/printcap or set using the -P option.
-Uuser: Execute commands as if they were made by user.
-V: Print version number, then exit.

Commands

?, help [commands]: Get a list of commands or help on specific commands.
active [printer@host]: Report whether lpd server is active.
abort all|printer: Terminate current printer daemon and disable printing for the specified printer.
class all|printer restriction: Restrict class of jobs being printed. restriction may be a class, a glob match on a particular control file entry of the form X=globmatch, or the word off to remove any existing restrictions.
clean all|printer: Remove files that cannot be printed from the specified printer queues.
client all|printer: Show LPRng client configuration and printcap information.
defaultq: List the default lpc queue.
defaults: List lpc's default configuration information.
disable all|printer: Disable specified printer queues.
down all|printer message: Disable specified printer queues and put message in the printer status file.
enable all|printer: Enable the specified printer queues.
exit, quit: Exit lpc.
help: Print help message.
hold printer [jobid]: Hold jobs in the queue. Release with the release command.
holdall all|printer: Automatically hold all new jobs until they are released with the release command.
kill all|printer: The same as performing abort followed by start. Although it is a convenient shorthand, sometimes the start command will not work due to race conditions.
lpd [printer@host]: Determine if lpd process is running. Report PID if it is.
lpq printer [options]: Run lpq command from inside lpc.
lprm printer jobid: Run lprm command from inside lpc to remove one or more print jobs.
move source jobid destination: Move specified jobs from source printer to destination printer.
msg printer message: Change printer status message to message. An empty message removes the current status message.
noholdall all|printer: Cancel holdall command.
quit, exit: Exit lpc program.
redirect source destination: Redirect all jobs sent to source printer to destination printer. If destination is off, turn off redirection.
redo printer jobid: Reprint jobs.
release printer [jobid]: Release held jobs for printing.
reread [printer@host]: Request lpd server to reread configuration and printcap information.
server all|printer: Show printcap entries as used by lpd.
start all|printer: Enable the printer queues and start printing daemons for the specified printers.
status all|printer: Return the status of the specified printers.
stop all|printer: Disable the specified printer daemons after any current jobs are completed.
topq printer [jobid] [users]: Put the specifed jobs at the top of the printer's queue in the order the jobs are listed.
up all|printer

lpd

lpd [options]

TCP/IP command. LPRng line printer daemon. lpd is usually invoked at boot time from the rc2 file. It makes a single pass through the printer configuration file (traditionally /etc/printcap) to find out about the existing printers, and prints any files left after a crash. It then accepts requests to print files in a queue, transfer files to a spooling area, display a queue's status, or remove jobs from a queue. In each case, it forks a child process for each request, then continues to listen for subsequent requests.

A file lock in each spool directory prevents multiple daemons from becoming active simultaneously. After the daemon has set the lock, it scans the directory for files beginning wth cf. Lines in each cf file specify files to be printed or nonprinting actions to be performed. Each line begins with a key character, which specifies information about the print job or what to do with the remainder of the line. Key characters are:

c: cifplot file.
d: DVI file.
f: Formatted file--name of a file to print that is already formatted.
g: Graph file.
l: Formatted file, but suppress pagebreaks and printing of control characters.
n: ditroff file.
p: File filtered using pr.
t: troff file.
v: File containing raster image.
C: Classification--string to be used for the classification line on the burst page.
H: Hostname--name of machine where lpd was invoked.
I: Indentation--number of characters to indent output.
J: Job name--string to be used for the jobname on the burst page.
L: Literal--contains identification information from the password file and causes the banner page to be printed.
M: Mail--send mail to the specified user when the current print job completes.
N: Filename--original name of data file to be printed.
P: Person--login name of person who invoked lpd.
T: Title--string to be used as the title for pr.
U: Unlink--name of file to remove upon completion of printing.
W: Width--page width in number of characters.

Options

-p port: Bind lpd to port instead of the default determined by getservbyname, usually port 515.
-F: Run lpd in foreground instead of as a daemon.
-L file: Log error and debugging messages to file instead of syslogd.
-V: Print version, then exit.

Files

/etc/lpd.conf: LPRng configuration file.
/etc/printcap: Printer description file.
/etc/lpd.perms: Printer permissions.
/var/spool/*: Spool directories.
/var/spool/*/printcap: Printer-specific description file.
/var/spool/*/printer: Queue lock file.
/var/spool/*/control.printer: Queue control.
/var/spool/*/active.printer: Active job.
/dev/lp*

lpq

lpq [options] [jobid]

Check the print spool queue for status of print jobs. For each job, display username, rank in the queue, filenames, job number, and total file size (in bytes). If user is specified, display information only for that user. jobid can be one or more job numbers, usernames, lpd key characters, or key character and glob patterns of the form X=pattern.

Options

-a: Report on all printers listed in the server's printcap database.
-l: Verbose mode. Print information about each file comprising a job. Use -l multiple times to increase the information provided.
-s: Print one-line status summary for each queue and subqueue.
-A: Use authentication.
-L: Maximum verbosity. Print all available information about each file comprising a job in a long display format.
-Pprinter: Specify which printer to query. Without this option, lpq uses the printer set in the PRINTER or other printer-related environment variables or the default system printer.
-V: Print version, then exit.
-tn: Display spool queues every n seconds.

lpr

lpr [options] [files]

The LPRng print spooler. Send files to the printer spool queue. If no files are given, accept standard input. On most Linux distributions, the LPRng print spooler replaces the BSD print spooler. Some systems use the alternative CUPS printing system. Both printing systems have lpr commands with options that are mostly compatible with BSD's lpr. We document LPRng's lpr command here.

Options

-b, -l: Expect a binary or literal file on which minimial processing should be done. The file is assigned filter f, which passes it through the default input filter (:if or :filter in the printcap file).
-f: Use a filter that interprets the first character of each line as a standard carriage control character.
-h: Do not print the burst page.
-i [cols]: Indent the output. Default is 8 columns. Specify number of columns to indent with the cols argument.
-k: Send data directly to the remote printer instead of creating a temporary file. This may cause problems if the job is killed when transferring the file, but can speed up large jobs.
-l: Use a filter that allows control characters to be printed and suppresses pagebreaks.
-m address: Send mail to address if print job is unsuccessful.
-w n: Set page width to n characters.
-A: Use authentication.
-B: Filter all job files as specified in the printcap database, then combine them into a single job file to be sent to the spooler.
-C class: Set the job classification used on the burst page and to assign priorities. class should be a letter from A to Z, A being the lowest priority and Z the highest.
-F filter: Set the print filter to use when printing files. filter should be a lowercase letter. The default is f. The command used for each filter is defined in the printer's printcap file.
-G: Filter individual jobs before sending them to the spooler.
-J name: Replace the job name on the burst page with name. If omitted, use the first file's name or STDIN.
-K n, #n: Print n copies of each listed file.
-Pprinter: Output to printer instead of the printer specified in the PRINTER environment variable or the system default.
-R name: Place additional accounting information in the R field of the control file.
-T title: Use title as the title when using pr.
-U user: Specify a username for the job. Available only for privileged users.
-V: Verbose mode. Print additional information about progress of the print job. Additional -V options may be given to increase the level of information printed.
-X command: Use the specified external command to filter files.
-Y host%port: Bypass the print spooler. Connect directly to the specified host and port and send the filtered file.
-Z options: Pass additional options through to the print spooler.

Obsolete options

The following options are all obsolete, though still functional. They may be removed in later versions of lpr. We include them here for those working with older systems or updating legacy shell scripts.

-c: Expect data produced by cifplot. Use filter c.
-d: Expect data produced by T_EX in the DVI (device-independent) format. Use filter d.
-g: Expect standard plot data produced by the plot routines. Use filter g.
-n: Expect data from ditroff (device-independent troff). Use filter n.
-p: Expect data preprocessed by the pr command. Use default filter f. This function may not be supported on some systems.
-r: Remove files upon completion of spooling. Mostly for compatibility with Berkeley lpr.
-t: Expect data from troff (phototypesetter commands). Use filter t.
-v: Expect a raster image for devices like the Benson Varian. Use filter v.

lprm

lprm [options] [jobid]

Remove a print job from the print spool queue. You must specify a job number or numbers, which can be obtained from lpq. A jobid can be one or more job numbers, usernames, lpd key characters, or key character and glob patterns of the form X=pattern. It can also be the keyword all, which matches all jobs. Only a privileged user may remove files belonging to another user.

Options

-a: Remove all jobs available to the user. Same as using the jobid ALL.
-A: Use authentication.
-P printer: Specify printer queue. Normally, the default printer or printer specified in the PRINTER environment variable is used.
-U user: Remove files as if command were executed by user. Only a privileged user can use this option.
-V: Print version, then exit.

lpstat

lpstat [options] [queues]

Show the status of the print queue or queues. With options that take a list argument, omitting the list produces all information for that option. list can be separated by commas or, if enclosed in double quotes, by spaces. For the LPRng print service, lpstat is a frontend to the lpq program.

Options

-a [list]: Show whether the list of printer or class names is accepting requests.
-c [list]: Show information about printer classes named in list.
-d: Show the default printer destination.
-f [list]: Verify that the list of forms is known to lp.
-l: Use after -f to describe available forms, after -p to show printer configurations, or after -s to describe printers appropriate for the specified character set or print wheel.
-o [list]: Show the status of output requests. list contains printer names, class names, or request IDs.
-p [list]: Show the status of printers named in list.
-r: Show whether the print scheduler is on or off.
-s: Summarize the print status (show almost everything).
-t: Show all status information (report everything).
-u [list]: Show request status for users on list. Use all to show information on all users.
-A: Use authentication.

ls [options] [names]

List contents of directories. If no names are given, list the files in the current directory. With one or more names, list files contained in a directory name or that match a file name. names can include filename metacharacters. The options let you display a variety of information in different formats. The most useful options include -F, -R, -l, and -s. Some options don't make sense together (e.g., -u and -c).

Options

-1, --format=single-column: Print one entry per line of output.
-a, --all: List all files, including the normally hidden files whose names begin with a period.
-b, --escape: Display nonprinting characters in octal and alphabetic format.
-c, --time-ctime, --time=status: List files by status change time (not creation/modification time).
--color =when: Colorize the names of files depending on the type of file. Accepted values for when are never, always, or auto.
-d, --directory: Report only on the directory, not its contents.
-f: Print directory contents in exactly the order in which they are stored, without attempting to sort them.
--full-time: List times in full, rather than use the standard abbreviations.
-g: Long listing like -l, but don't show file owners.
-h: Print sizes in kilobytes and megabytes.
--help: Print a help message and then exit.
-i, --inode: List the inode for each file.
--indicator-style=none: Display filenames without the flags assigned by -p or -f (default).
-k, --kilobytes: If file sizes are being listed, print them in kilobytes. This option overrides the environment variable POSIXLY_CORRECT.
-l, --format=long, --format=verbose: Long format listing (includes permissions, owner, size, modification time, etc.).
-m, --format=commas: Merge the list into a comma-separated series of names.
-n, --numeric-uid-gid: Like -l, but use group ID and user ID numbers instead of owner and group names.
-o: Long listing like -l, but don't show group information.
-p, --filetype, --indicator-style=file-type: Mark directories by appending / to them.
-q, --hide-control-chars: Show nonprinting characters as ? (default for display to a terminal).
-r, --reverse: List files in reverse order (by name or by time).
-s, --size: Print file size in blocks.
--show-control-chars: Show nonprinting characters verbatim (default for printing to a file).
--si: Similar to -h, but uses powers of 1000 instead of 1024.
-t, --sort=time: Sort files according to modification time (newest first).
-u, --time=atime, --time=access, --time=use: Sort files according to file access time.
--version: Print version information on standard output, then exit.
-x, --format=across, --format=horizontal: List files in rows going across the screen.
-v, --sort=version: Interpret the digits in names such as file.6 and file.6.1 as versions, and order filenames by version.
-w, --width=n: Format output to fit n columns.
-A, --almost-all: List all files, including the normally hidden files whose names begin with a period. Does not include the . and .. directories.
-B, --ignore-backups: Do not list files ending in ~ unless given as arguments.
-C, --format=vertical: List files in columns (the default format).
-D, --dired: List in a format suitable for Emacs dired mode.
-F, --classify, --indicator-style=classify: Flag filenames by appending / to directories, * to executable files, @ to symbolic links, | to FIFOs, and = to sockets.
-G, --no-group: In long format, do not display group name.
-H, --dereference-command-line: When symbolic links are given on the command line, follow the link and list information from the actual file.
-I, --ignore pattern: Do not list files whose names match the shell pattern pattern unless they are given on the command line.
-L, --dereference: List the file or directory referenced by a symbolic link rather than the link itself.
-N, --literal: Display special graphic characters that appear in filenames.
-Q, --quote-name: Quote filenames with "; quote nongraphic characters.
-R, --recursive: List directories and their contents recursively.
-S, --sort=size: Sort by file size, largest to smallest.
-Rfile, --reload-state file: Load state from file before starting execution.
-U, sort=none: Do not sort files.
-X, sort=extension

lsattr

lsattr [options] [files]

Print attributes of files on a Linux Second Extended File System. See also chattr.

Options

-a: List all files in specified directories.
-d: List attributes of directories, not of contents.
-v: List version of files.
-R: List directories and their contents recursively.
-V: List version of lsmod, then exit.

lsmod

lsmod

System administration command. List all loaded modules: name, size (in 4KB units), and, if appropriate, a list of referring modules. The same information is available in /proc/modules if the /proc directory is enabled on the system.

Options

-h, --help: Show usage.
-V, --version: Show version of this command.

m4 [options] [macros] [files]

Macro processor for C and other files.

Options

-e, --interactive: Operate interactively, ignoring interrupts.
-dflags, --debug=flags: Specify flag-level debugging.
--help: Print help message, then exit.
-ln, --arglength=n: Specify the length of debugging output.
-o file, --error-output=file: Place output in file. Despite the name, print error messages on standard error.
-p, --prefix-built-ins: Prepend m4_ to all built-in macro names.
-s, --synclines: Insert #line directives for the C preprocessor.
-tname, --tracename: Insert name into symbol table as undefined. Trace macro from the point it is defined.
--version: Print version, then exit.
-Bn: Set the size of the pushback and argument collection buffers to n (default is 4096).
-Dname[=value], --define=name[=value]: Define name as value or, if value is not specified, define name as null.
-E, --fatal-warnings: Consider all warnings to be fatal, and exit after the first of them.
-Ffile, --freeze-state file: Record m4's frozen state in file for later reloading.
-G, --traditional: Behave like traditional m4, ignoring GNU extensions.
-Hn, --hashsize=n: Set symbol-table hash array to n (default is 509).
-Idirectory, --include=directory: Search directory for include files.
-Q, --quiet, --silent: Suppress warning messages.
-Rfile, --reload-state file: Load state from file before starting execution.
-Uname, --undefine=name: Undefine name.

mail

mail [options] [users]

Read mail or send mail to other users. The mail utility allows you to compose, send, receive, forward, and reply to mail. mail has two main modes: compose mode, in which you create a message, and command mode, in which you manage your mail.

While mail is a powerful utility, it can be tricky for a novice user. It is most commonly seen nowadays in scripts. Most Linux distributions include several utilities that are richer in features and much easier to use: mailers built in to browsers such as Netscape and Mozilla, graphical mail programs distributed with GNOME (Evolution) and KDE (Kmail), and the terminal-based, full-screen utilities pine and elm. The GNU Emacs editor can also send and receive mail.

This section presents mail commands, options, and files. To get you started, here are two of the most basic commands.

To enter interactive mail-reading mode, type:

mail

To begin writing a message to user, type:

mail user

Enter the text of the message, one line at a time, pressing Enter at the end of each line. To end the message, enter a single period (.) in the first column of a new line and press Enter.

Command-line options

-b list: Set blind carbon copy field to comma-separated list.
-c list: Set carbon copy field to comma-separated list.
-d: Print debugging information.
-f [file]: Process contents of file instead of /var/spool/mail/$user. If file is omitted, process mbox in the user's home directory.
-i: Do not respond to tty interrupt signals.
-n: Do not consult /etc/mail.rc when starting up.
-p: Read mail in POP mode.
-s subject: Set subject to subject.
-u: Process contents of /var/spool/mail/$user (the default).
-v: Verbose; print information about mail delivery to standard output.
-N: When printing a mail message or entering a mail folder, do not display message headers.
-P: Disable POP mode.

Compose-mode commands

~!: Execute a shell escape from compose mode.
~?: List compose-mode escapes.
~b names: Add names to or edit the Bcc: header.
~c names: Add names to or edit the Cc: header.
~d: Read in the dead.letter file.
~e: Invoke text editor.
~f messages: Insert messages into message being composed.
~F messages: Similar to ~f, but include message headers.
~h: Add to or change all headers interactively.
~m messages: Similar to ~f, but indent with a tab.
~M messages: Similar to ~m, but include message headers.
~p: Print message header fields and message being sent.
~q: Abort current message composition.
~r filename: Append file to current message.
~s string: Change Subject: header to string.
~t names: Add names to or edit the To: list.
~v: Invoke editor specified with the VISUAL environment variable.
~| command: Pipe message through command.
~: mail-command: Execute mail-command.
~~string: Insert string in text of message, prefaced by a single tilde (~). If string contains a ~, it must be escaped with a \.

Command-mode commands

?

!

Execute a shell command.

- num

Print numth previous message; defaults to immediately previous.

alias (a)

Print or create alias lists.

alternates (alt)

Specify remote accounts on remote machines that are yours. Tell mail not to reply to them.

chdir (c)

cd to home or specified directory.

copy (co)

delete (d)

Delete message.

dp

Delete current message and display next one.

edit (e)

Edit message.

exit (ex, x)

Exit mail without updating folder.

file (fi)

Switch folders.

folder (fold)

Read messages saved in a file. Files can be:

#: Previous
%: System mailbox
%user: user's system mailbox
&: mbox
+folder: File in folder directory.

folders

List folders.

headers (h)

List message headers at current prompt.

headers+ (h+)

Move forward one window of headers.

headers- (h-)

Move back one window of headers.

help

Same as ?.

hold (ho)

Hold messages in system mailbox.

ignore

Append list of fields to ignored fields.

mail user (m)

Compose message to user.

mbox

Move specified messages to mbox on exiting (the default).

next (n)

Type next message or next message that matches argument.

preserve (pr)

Synonym for hold.

print [list] (p)

Display each message in list.

Print [list] (P)

quit (q)

Exit mail and update folder.

reply (r)

Send mail to all on distribution list.

Reply (R)

Send mail to author only.

respond

Same as reply.

retain

Always include this list of header fields when printing messages. With no arguments, list retained fields.

save (s)

Save message to folder.

saveignore

Remove ignored fields when saving.

saveretain

Override saveignore to retain specified fields.

set (se)

Set or print mail options.

shell (sh)

Enter a new shell.

size

Print size of each specified message.

source

Read commands from specified file.

top

Print first few lines of each specified message.

type (t)

Same as print.

Type (T)

Same as Print.

unalias

Discard previously defined aliases.

undelete (u)

Restore deleted message.

unread (U)

Mark specified messages as unread.

unset (uns)

Unset mail options.

visual (v)

Edit message with editor specified by the VISUAL environment variable.

write (w)

Write message, without header, to file.

xit (x)

Same as exit.

z

Move mail's attention to next windowful of text. Use z- to move it back.

Options

These options are used inside the .mailrc file. The syntax is set option or unset option.

append: Append (do not prepend) messages to mbox.
ask: Prompt for subject.
askbcc: Prompt for blind carbon copy recipients.
askcc: Prompt for carbon copy recipients.
asksub: Prompt for Subject line.
autoprint: Print next message after a delete.
chron: Display messages in chronological order, most recent last.
debug: Same as -d on command line.
dot: Interpret a solitary . as an EOF.
folder: Define directory to hold mail folders.
hold: Keep message in system mailbox upon quitting.
ignore: Ignore interrupt signals from terminal. Print them as @.
ignoreeof: Do not treat ^D as an EOF.
metoo: Do not remove sender from groups when mailing to them.
noheader: Same as -N on command line.
nokerberos: Retrieve POP mail via POP3, not KPOP, protocol.
nosave: Do not save aborted letters to dead.letter.
pop-mail: Retrieve mail with POP3 protocol, and save it in mbox.pop.
prompt: Set prompt to a different string.
Replyall: Switch roles of Reply and reply.
quiet: Do not print version at startup.
searchheaders: When given the specifier /x:y, expand all messages that contain the string y in the x header field.
verbose: Same as -v on command line.
verbose-pop: Display status while retrieving POP mail.

Special files

calendar: Contains reminders that the operating system mails to you.
.maildelivery: Mail delivery configuration file.
.mailrc: Mail configuration file.
triplog: Keeps track of your automatic response recipients.
tripnote

mailq

mailq [options]

System administration command. List all messages in the sendmail mail queue. Equivalent to sendmail -bp.

Options

-Ac: Show queue specified in /etc/mail/submit.cf instead of queue specified in /etc/mail/sendmail.cf.
-v: Verbose mode.

mailstats

mailstats [options]

System administration command. Display a formatted report of the current sendmail mail statistics.

Options

-c: Use configuration in /etc/mail/submit.cf instead of /etc/mail/sendmail.cf.
-f file: Use sendmail statistics file file instead of the file specified in the sendmail configuration file.
-o: Don't show the name of the mailer in the report.
-p: Print stats without headers or separators. Output suitable for use by other programs. Reset statistics.
-C file: Use sendmail configuration file file instead of the default sendmail.cf file.
-P: Print stats without headers or separators. Output suitable for use by other programs. Do not reset statistics.

mailto

mailto [options] recipients

Send mail with MIME types and text formatting. This program has a very similar interface to that of the mail program, with two differences: it only sends mail, and it adds a number of text formatting and MIME handling features, described here. For features not covered here, check the mail command. mailto uses the metamail backend and relies on the mailcap configuration files.

Text formatting

Mail formatting is handled with escape sequences that begin with the tilde (~) character. Those for text formatting are:

~b: Turn bold text on or off.
~i: Turn italic text on or off.
~jc, ~jl, ~jr: Set justification to center, left, or right.
~k: Toggle whether to send a blind copy to yourself.
~n: Hard line break (newline).
~>, ~<: Increase or decrease left margin.
~<R, ~>R: Increase or decrease right margin.
~Q: Quotation mode (indent and mark selection as excerpt).
~z: Append ~/.signature as the signature for this message.

Including objects in mail

You can include a variety of objects in your messages, again using tilde escape sequences. To do so, enter ~*, and the program will prompt you for the type of data you wish to add. The available content types will vary from installation to installation.

make

make [options] [targets] [macro definitions]

Update one or more targets according to dependency instructions in a description file in the current directory. By default, this file is called makefile or Makefile. Options, targets, and macro definitions can be in any order. Macro definitions are typed as:

name=string

For more information on make, see Managing Projects with make (O'Reilly).

Options

-d, --debug: Print detailed debugging information.
-e, --environment-overrides: Override makefile macro definitions with environment variables.
-f makefile, --file=makefile, --makefile=makefile: Use makefile as the description file; a filename of - denotes standard input.
-h, --help: Print options to make command.
-i, --ignore-errors: Ignore command error codes (same as .IGNORE).
-j [jobs], --jobs [=jobs]: Attempt to execute jobs jobs simultaneously or, if no number is specified, as many jobs as possible.
-k, --keep-going: Abandon the current target when it fails, but keep working with unrelated targets.
-l [load], --load-average [=load], --max-load [=load]: Attempt to keep load below load, which should be a floating-point number. Used with -j.
-n, --just-print, --dry-run, --recon: Print commands but don't execute (used for testing).
-o file, --old-file=file, --assume-old=file: Never remake file or cause other files to be remade on account of it.
-p, --print-data-base: Print rules and variables in addition to normal execution.
-q, --question: Query; return 0 if file is up to date; nonzero otherwise.
-r, --no-built-in-rules: Do not use default rules.
-s, --silent, --quiet: Do not display command lines (same as .SILENT).
-t, --touch: Touch the target files without remaking them.
-v, --version: Show version of make.
-w, --print-directory: Display the current working directory before and after execution.
--warn-undefined-variables: Print warning if a macro is used without being defined.
-C directory, --directory directory: cd to directory before beginning make operations. A subsequent -C directive will cause make to attempt to cd into a directory relative to the current working directory.
-I directory, --include-dir directory: Include directory in list of directories containing included files.
-S, --no-keep-going, --stop: Cancel previous -k options. Useful in recursive makes.
-W file, --what-if file, --new-file file, --assume-new file: Behave as though file has been recently updated.

Description file lines

Instructions in the description file are interpreted as single lines. If an instruction must span more than one input line, use a backslash (\) at the end of the line so that the next line is considered a continuation. The description file may contain any of the following types of lines:

Blank lines

Blank lines are ignored.

Comment lines

A pound sign (#) can be used at the beginning of a line or anywhere in the middle. make ignores everything after the #.

Dependency lines

Depending on one or more targets, certain commands that follow will be executed. Possible formats include:

targets : dependencies
targets : dependencies ; command

Subsequent commands are executed if dependency files (the names of which may contain wildcards) do not exist or are newer than a target. If no prerequisites are supplied, then subsequent commands are always executed (whenever any of the targets are specified). No tab should precede any targets.

Conditionals

Conditionals are evaluated when the makefile is first read and determine what make sees, i.e., which parts of the makefile are obeyed and which parts are ignored. The general syntax for a conditional is:

conditional
Text if true
else
Text if false
endif

ifeq (arg1, arg2), ifeq "arg1" "arg2"

True if the two arguments are identical. The arguments should either be placed in parentheses and separated by a comma--(arg1, arg2)--or individually quoted with either single or double quotes.

ifneq (arg1, arg2), ifneq "arg1" "arg2"

True if the two arguments are not identical. The arguments should either be placed in parentheses and separated by a comma or individually quoted with either single or double quotes.

ifdef variable

True if variable has a nonempty value.

ifndef variable

True if variable has an empty value.

Suffix rules

These specify that files ending with the first suffix can be prerequisites for files ending with the second suffix (assuming the root filenames are the same). Either of these formats can be used:

.suffix.suffix:
.suffix:

The second form means that the root filename depends on the filename with the corresponding suffix.

Commands

Commands are grouped below the dependency line and are typed on lines that begin with a tab. If a command is preceded by a hyphen (-), make ignores any error returned. If a command is preceded by an at sign (@), the command line won't echo on the display (unless make is called with -n).

Macro definitions

These have the following form:

name = string

or:

define name
string
endef

Blank space is optional around the =.

Include statements

include files

Internal macros

$?

Pattern rules

These are a more general application of the idea behind suffix rules. If a target and a dependency both contain %, GNU make will substitute any part of an existing filename. For instance, the standard suffix rule:

$(cc) -o $@ $<

can be written as the following pattern rule:

%.o : %.c
$(cc) -o $@ $<

Macro modifiers

D

makedbm [options] infile outfile
makedbm [option]

NFS/NIS command. Create or dump an NIS dbm file. makedbm will take a text infile and convert it to a gdbm database file named outfile. This file is suitable for use with ypserv. Each line of the input file is converted to a single record. All characters up to the first TAB or SPACE form the key, and the rest of the line is the data. If a line ends with \&, the data for that record is continued on to the next line. The # character is given no special treatment. infile can be -, in which case the standard input is read.

makedbm generates two special keys: the YP_MASTER_NAME key, which is the value of the current host (unless another name is specified with -m), and the YP_LAST_MODIFIED key, which is the date of infile (or the current time if infile is -).

Options

-a: Add support for mail aliases.
-b: Insert YP_INTERDOMAIN key into map. This indicates that ypserv should fall back to DNS lookups when a host's address is not found in NIS.
-c: Send a YPPROC_CLEAR signal to ypserv, causing it to clear all cached entries.
-i file_name: Create a YP_INPUT_NAME key with the value file_name.
-l: Convert keys of the given map to lowercase.
-m master_name: Specify the value of the YP_MASTER_NAME key. The default value is the current hostname.
--no-limit-check: Don't enforce NIS size limits for keys or data.
-o file_name: Create a YP_OUTPUT_NAME key with the value file_name.
-r: Treat lines beginning with # as comments. Do not include them in the data file.
-s: Add the key YP_SECURE, indicating that ypserv should accept connections to the database only from secure NIS networks.
-u filename: Undo a gdbm file--print out a dbm file, one entry per line, with a single space separating keys from values.

Example

It is easy to write shell scripts to convert standard files such as /etc/passwd to the key value form used by makedbm. For example, the awk program:

BEGIN { FS =":";OFS = "\t";}
{ print $1, $0}

takes the /etc/passwd file and converts it to a form that can be read by makedbm to make the NIS file passwd.byname. That is, the key is a username and the value is the remaining line in the /etc/passwd file.

makemap

makemap [options] type name

System administration command. Create database maps for use by sendmail in keyed map lookups. makemap will read from standard input and create a database file of type type with filename name.db. If the TrustedUser option is set in /etc/sendmail.cf and makemap is invoked as root, the ouput file will be owned by TrustedUser.

Input should be formatted as:

key value

Comment lines with #. Indicate parameter substitution with %n. Specify a literal % character by entering it twice: %%. The type may be btree or hash.

Options

-c size: Specify hash or B-Tree cache size.
-d: Allow duplicate entries. Valid only with btree type maps.
-e: Allow empty value data fields.
-f: Suppress conversion of uppercase to lowercase.
-l: List supported map types.
-o: Append to existing file instead of replacing it.
-r: If some keys already exist, replace them. (By default, makemap will exit when encountering a duplicated key.)
-s: Ignore safety checks.
-t delimiter: Use delimiter instead of whitespace.
-u: Undo a map--print out the specified database file, one entry per line.
-v: Verbose mode.
-C file: Look up TrustedUser in the specified sendmail configuration file.
-N: Append the zero-byte string terminator specified in sendmail's configuration file to mapped entries.

man

man [options] [section] [title]

Display information from the online reference manuals. man locates and prints the named title from the designated reference section.

Traditionally, manpages are divided into nine sections, where section 1 consists of user commands, section 2 contains system calls, and so forth. By default, all sections are consulted, so the section option serves to bypass the most common entry and find an entry of the same name in a different section (e.g., man 2 nice).

Numerous other utilities, such as info, xman, and the Konqueror browser, can also display manpages.

Options

-7, --ascii: Expect a pure ASCII file, and format it for a 7-bit terminal or terminal emulator.
-a, --all: Show all pages matching title.
-b: Leave blank lines in output.
-d, --debug: Display debugging information. Suppress actual printing of manual pages.
-f, --whatis: Same as whatis command.
-k, --apropos: Same as apropos command.
-l, --local-file: Search local files, not system files, for manual pages. If i is given as filename, search standard input.
-m systems, --systems=systems: Search systems' manual pages. systems should be a comma-separated list.
-p preprocessors, --preprocessor=preprocessors: Preprocess manual pages with preprocessors before turning them over to nroff, troff, or groff. Always runs soelim first to read in files to be included in this one. preprocessors can be any combination of e for equations, p for pictures, t for tables, and r for bibliographical references.
-r prompt, --prompt=prompt: Set prompt if less is used as pager.
-t, --troff: Format the manual page with /usr/bin/groff -Tgv -mandoc. Implied by -T and -Z.
-u, --update: Perform a consistency check between manual page cache and filesystem.
-w, -W, --path, --where: Print pathnames of entries on standard output.
-D: Display debugging information about how the page was retrieved.
-K directory: A kind of super-k option. Search for a term in all manpages and display the name of each page, along with a prompt asking whether you want to view the page.
-L locale, --locale=locale: Assume current locale to be locale; do not consult the setlocale( ) function.
-M path, --manpath=path: Search for manual pages in path. Ignore -m option.
-Ppager, --pager=pager: Select paging program pager to display the entry.
-S sections: Sections to look in for an entry. Like specifying section on the command line, except that multiple section numbers can be specified, separated by colons.
-T device, --troff-device[=device]: Format groff or troff output for device, such as dvi, latin1, X75, and X100.
-Z, --ditroff: Do not allow postprocessing of manual page after groff has finished formatting it.

Section names

Manual pages are divided into sections for various audiences:

1: Executable programs or shell commands.
2: System calls (functions provided by the kernel).
3: Library calls (functions within system libraries).
4: Special files (usually found in /dev).
5: File formats and conventions (e.g., /etc/passwd).
6: Games.
7: Macro packages and conventions.
8: System administration commands (usually only for a privileged user).
9

manpath

manpath [options]

Attempt to determine path to manual pages. Check $MANPATH first; if that is not set, consult /etc/man.conf, user environment variables, and the current working directory. The manpath command is a symbolic link to man, but most of the options are ignored for manpath.

Options

-d, --debug: Print debugging information.
-h: Print help message and then exit.

mattrib

mattrib [options] filenames

Change attributes of MS-DOS files. See mtools for more information.

Attributes

To set an attribute, use one of the following letters preceded by a + (to turn the attribute on) or - (to turn it off):

a: Archive; mark the file as a new file that should be archived by backup programs.
r: Read-only.
s: System; files with this attribute are marked as operating system files.
h: Hide this file when displaying directory contents with DIR.

Options

-/: When listing attributes, descend into all subdirectories recursively.
-X: Concise output.
-P: Display commands for mformat that can reproduce the current attributes and settings for a given disk.

mbadblocks

mbadblocks drive

Check MS-DOS filesystems for bad blocks. See badblocks and mtools. As with other mtools items, the drive is named with a letter rather than as a Unix device.

mcat

mcat [option] drive

Dump raw data, especially for a disk image on a remote floppy accessed through the floppyd tool. See cat and mtools for more information. The only option accepted, -w, accepts data from stdin and writes it to the given device.

mcd

mcd drive

Change directory on an MS-DOS disk. See cd and mtools for more information.

mcopy

mcopy [options] sourcefile target

Copy files between Unix and MS-DOS format partitions. See cp and mtools for more information.

Options

The mcopy option flags differ from the flags passed to the Unix cp command. The flags are:

-t: Convert Unix line breaks to MS-DOS line breaks and vice versa when copying text files.
-b: Operate in batch mode; use for large copies of data.
-s: Copy recursively.
-P: Preserve attributes of copied files.
-Q: If one copy fails, stop copying the rest. Useful if you think you may run out of disk space.
-a: Assume that all incoming files are ASCII and convert carriage return/line feed to plain line feed.
-T: Convert line breaks as with -a, but also convert PC-8 characters to ISO-8859-1 characters. Replace untranslatable characters with # or . for Unix and DOS respectively.
-n: Do not ask for confirmation when overwriting Unix files. Use -o to turn off confirmation for overwriting DOS files.
-m: Preserve file modification time.
-v: Display the names of files as they are copied.
-D clash-option: Specify the action to take if the specified directory name already exists. See mmd for the possible clash options.

mdel, mdeltree

mdel [option] filemdeltree [option] tree

Delete an MS-DOS file or file tree. See rm and mtools for more information.

Option

-v: Run in verbose mode, printing the names of the MS-DOS files to be deleted.

mdir

mdir [options] dir

List directory contents on an MS-DOS filesystem. See ls, dir, and mtools for more information.

Options

-/: Display output recursively, listing the contents of subdirectories.
-a: Include hidden files in the output.
-b: Produce a concise listing, showing each directory or file on a separate line, with no heading or summary information.
-f: Operate in fast mode, without determining the amount of free space. Not required on FAT32 filesystems, which store the free space information explicitly.
-w: Produce wide output, printing filenames across the page with no file size or creation date information.
-V: Print version information and exit.

mdu

mdu [option] dir

Display disk usage, in clusters, for a directory and its subdirectories and files on an MS-DOS filesystem. See du and mtools for more information, and see minfo for the cluster size. Only one of -a or -s can be specified.

Options

-a: Show the space used by individual files in a directory as well as the total space.
-s: Show only the total space used.

merge

merge [options] file1 file2 file3

Perform a three-way file merge. The effect is easiest to understand if file2 is considered the original version of a file, file3 an altered version of file2, and file1 a later altered version of file2.

After the merge, file1 contains both the changes from file2 to file1 and the changes from file2 to file3. In other words, file1 keeps its changes and incorporates the changes in file3 as well. merge does not change file2 or file3.

If a line from file2 was changed in different ways in both file1 and file3, merge recognizes a conflict. By default, the command outputs a warning and puts brackets around the conflict, with lines preceded by <<<<<<< and >>>>>>>. A typical conflict looks like this:

<<<<<<< file1
relevant lines from file1
=  ==  ==  ==
relevant lines from file3
>>>>>>> file3

If there are conflicts, the user should edit the result and delete one of the alternatives.

Options

-e

Don't warn about conflicts.

-p

Send results to standard output instead of overwriting file1.

-q

Quiet; do not warn about conflicts.

-A

Output conflicts using the -A style of diff3. This merges all changes leading from file2 to file3 into file1 and generates the most verbose output.

-E

Output conflict information in a less verbose style than -A; this is the default.

-L label

Specify up to three labels to be used in place of the corresponding filenames in conflict reports. That is:

merge -L x -L y -L z file_a file_b file_c

generates output that looks as if it came from x, y, and z instead of from file_a, file_b, and file_c.

-V

Print version number.

mesg

mesg [option]

Change the ability of other users to send write messages to your terminal. With no options, display the permission status.

Options

n: Forbid write messages.
y: Allow write messages (the default).

metamail

metamail [options] [filename]

Normally invisible to users, metamail is used to send and display rich text or multimedia email using MIME typing metadata. Mail-reading programs normally call metamail to determine how to handle the data, but metamail can be called directly by developers who want to use it for their own mail software, or by system administrators and power users adding lines to their printcap files. Any argument passed to metamail that is not preceded by a hyphen (-) is assumed to be the name of a file to read. If no filename is specified, standard input is assumed.

Options

-b: The message is not in RFC 822 format; treat as the body of the message. Requires -c.
-B: Display the message in the background, if noninteractive. Cannot be used with -p or -P.
-c type: Use the specified content type instead of the one in the headers.
-d: Don't ask before running an interpreter to view the message. The default is to ask.
-e: Remove ("eat") leading newlines in the message body. Useful for MH-format mail.
-f addr: Specify the name of the message sender. The default is to try to determine the name from the header.
-h: Specify that a message is to be printed. Automatically sets -d.
-m mailer: Specify the mail program to be called by metamail.
-p: If necessary, display the output one page at a time. The default is to pipe the output through more, but the environment variable METAMAIL_PAGER can be set to specify an alternative command. Use -p rather than piping the message to a pager.
-P: Like -p, but also print "Press RETURN to go on" at the end of each page. Cannot be used with -B.
-q: Run quietly.
-r: Specify that metamail can be run as root.
-R: Run /usr/ucb/reset to reset the terminal before performing any other I/O.
-s subject: Specify the Subject field. By default, the subject is determined from the headers.
-T: Turn off the effect of the environment variable MM_TRANSPARENT. Intended to be used recursively by metamail, and should be used only when the program restarts itself in a terminal emulator window.
-w: Don't consult a mailcap file to determine how to display the data, but simply decode each part and write to a file in its raw format (which might be binary). Depending on how metamail is called, the filename is determined from the message headers, by asking the user, or by generating a unique temporary filename.
-x: Tell metamail that it is not running on a terminal. The environment variable MM_NOTTY can be set instead of specifying -x.
-y: Try to "yank" a MIME-format message from the body of the message.
-z: Delete the input file when done.

metasend

metasend [options] [filename]

A largely developer-oriented interface for sending non-text email using MIME typing metadata. If no arguments are specified, metasend prompts the user for the information it needs. See mailto for a possible alternative with a friendlier interface.

Options

-/ subtype: Specify the MIME multipart subtype other than mixed.
-b: Batch mode. All information must be provided on the command line.
-c cc: Specify any CC addresses.
-D string: Specify a string to be used as the Content-description value.
-e encoding: Specify the encoding to use. Possible values are base64, quoted-printable, 7bit (no encoding is done), or x-uue.
-E: The file to be included is already MIME-encoded and doesn't need any Content- or other header fields added.
-f file: The file to be included. If more than one file is specified with separate -f options (see -n), they are combined into a single multipart MIME object.
-F from: The From address.
-i content-id: The content ID value for the MIME entity. Must be a valid content ID enclosed in angle brackets (<>).
-I content-id: The content ID value for a multipart entity being created by metasend. Must be a valid content ID enclosed in angle brackets (<>).
-m type: The MIME content type.
-n: Specify that an additional file is to be included. Must appear after one occurrence of at least -m, -c, and -f and must be specified for each included file.
-ooutfile: Send the output to the specified file instead of delivering as mail.
-P preamblefile: Specify a file containing alternative text for the preamble portion of a multipart MIME message.
-s subject: The Subject field.
-S splitsize: Specify the maximum size before the file is split into parts to be sent separately.
-t to: The To field.
-z: Delete temporary files even if the send fails.

mformat

mformat [options] drive

Format a blank disk in MS-DOS format. See mtools for more information about how to handle MS-DOS filesystems. After using mformat to format a disk, you should use mbadblocks to check for bad blocks.

Options

The mformat command accepts many of the same options as the MS-DOS FORMAT command:

-v [label]: Choose a label for this volume. Maximum length is 11 characters.
-f N: If you are using a floppy disk, use this flag and note the size of the disk in kilobytes as 160, 180, 320, 360, 720, 1200, 1440, or 2280. For most relatively recent systems, only the last two are relevant. If you are not using a floppy, you must use the -h, -t, or -n flags.
-t N: The number of tracks on the disk.
-h N: The number of heads, or sides, on the disk (either 1 or 2).
-n: The number of sectors per track.

You can also use a number of option flags that are not included in the MS-DOS version of FORMAT, including:

-F: Format as a FAT32 partition.
-S N: Size code. You are defining a sector that is the N+7th power of two.
-X: Format as an XDF (OS/2) disk.
-2: Use a 2m format.
-3: Don't use a 2m format, even if the disk looks like a 2m disk.
-C: Create a disk image file. Useful only for virtual disks.
-M N: Set the software sector size to be different from the physical sector size.
-N serialno: Choose a serial number. Use -a for an Atari-style serial number, stored in the OEM label.
-c N: Set the cluster size to N sectors.
-r N: Set the root directory size to N sectors for 12- and 16-bit FAT formats.
-L N: Set the length of the File Allocation Table (FAT).

mimencode

mimencode [options] [filename] [-o output_file]

Translate to and from MIME encoding formats, the proposed standard for Internet multimedia mail formats. By default, mimencode reads standard input and sends a base64-encoded version of the input to standard output.

Options

-b: Use the (default) base64 encoding.
-o output_file: Send output to the named file rather than to standard output.
-p: Translate decoded CRLF sequences into the local newline convention during decoding, and do the reverse during encoding. This is meaningful only when the default base64 encoding is in effect.
-q: Use the quoted-printable encoding instead of base64.
-u: Decode the standard input rather than encode it.

minfo

minfo [options] drive

Display information about an MS-DOS filesystem. See mtools for more information.

mkdir

mkdir [options] directories

Create one or more directories. You must have write permission in the parent directory in order to create a directory. See also rmdir. The default mode of the new directory is 0777, modified by the system or user's umask.

Options

-m, --mode mode: Set the access mode for new directories. See chmod for an explanation of acceptable formats for mode.
-p, --parents: Create intervening parent directories if they don't exist.
--verbose: Print a message for each directory created.
--help: Print help message and then exit.
--version: Print version number and then exit.

Examples

Create a read-only directory named personal:

mkdir -m 444 personal

The following sequence:

mkdir work; cd work
mkdir junk; cd junk
mkdir questions; cd ../..

can be accomplished by typing this:

mkdir -p work/junk/questions

mkdosfs

mkdosfs [options] device [blocks]mkfs.msdos [options] device [blocks]

System administration command. Format device as an MS-DOS filesystem. You may specify the number of blocks on the device or allow mkdosfs to guess.

Options

-b backup-sector: Specify sector for backup boot sector. The default value depends on the number of reserved sectors, but is usually sector 6.
-c: Scan device for bad blocks before execution.
-f n: Specify number of File Allocation Tables (FATs) to create (either 1 or 2).
-i volume-id: Use the specified 32-bit hexadecimal volume-id instead of calculating a number based on the time of creation.
-l file: Read list of bad blocks from file.
-m message-file: Set the message to be used when the filesystem is booted without an installed operating system to the contents of the file message-file. The message may be up to 418 bytes in size. If filename is a hyphen, read text from standard input.
-n label: Set volume name for filesystem to label. The volume name may be up to 11 characters long.
-r maximum-entries: Set the maximum-entries allowed in the root directory. The default is 112 or 224 for floppies and 512 for hard disks.
-s sectors: Set the number of disk sectors per cluster. The number must be a power of 2.
-v: Print verbose information about progress.
-A: Create an Atari MS-DOS filesystem.
-C: Create and format a file suitable for use on a floppy disk. The device given on the command line should be a filename, and the number of blocks must also be specified.
-F fat-size: Create File Allocation Tables (FATs) of size fat-size. By default this will be between 12 and 16 bits. Set to 32 to create a FAT32 filesystem.
-I: Force installation to a device without partitions. This is useful when formating magneto-optical disks.
-R reserved-sectors: Create the specified number of reserved-sectors. The default depends on the size of the File Allocation Table (FAT). For 32-bit FAT, the default is 32; for all other sizes, the default is 1.
-S sector-size: Create logical sectors of sector-size bytes. Size must be a power of 2 and at least 512 bytes.

mke2fs

mke2fs [options] device [blocks]
mkfs.ext2 [options] device [blocks]

System administration command. Format device as a Linux Second Extended Filesystem. You may specify the number of blocks on the device or allow mke2fs to guess.

Options

-b block-size

Specify block size in bytes.

-c

Scan device for bad blocks before execution.

-f fragment-size

Specify fragment size in bytes.

-i bytes-per-inode

Create an inode for each bytes-per-inode of space. bytes-per-inode must be 1024 or greater; it is 4096 by default.

-j

Create an ext3 journal. This is the same as invoking mkfs.ext3.

-l filename

Consult filename for a list of bad blocks.

-m percentage

Reserve percentage percent of the blocks for use by privileged users.

-n

Don't create the filesystem, just show what would happen if it were run. This option is overridden by -F.

-o os

Set filesystem operating system type to os. The default value is usually Linux.

-q

Quiet mode.

-r revision

Set filesystem revision number to revision.

-v

Force mke2fs to run even if filesystem is mounted or device is not a block special device. This option is probably best avoided.

-F

-J parameterlist

Use specified parameterlist to create an ext3 journal. The following two parameters may be given in a comma-separated list:

size=journal-size: Create a journal of journal-size megabytes. The size may be between 1024 filesystem blocks and 102,400 filesystem blocks in size (e.g., 1-100 megabytes if using 1K blocks, 4-400 megabytes if using 4K blocks).
device=journal-device: Use an external journal-device to hold the filesystem journal. The journal-device can be specified by name, by volume label, or by UUID.

-L label

Set volume label for filesystem.

-M directory

Set the last mounted directory for filesystem to directory.

-N inodes

Specify number of inodes to reserve for filesystem. By default, this number is calculated from number of blocks and inode size.

-O featurelist

Use specified featurelist to create filesystem. The sparse_super and filetype features are used by default on kernels 2.2 and later. The following parameters may be given in a comma-separated list:

filetype: Store file type information in directory entries.
has_journal: Create an ext3 journal. Same as using the -j option.
journal_dev: Prepare an external journaling device by creating an ext3 journal on device instead of formatting it.
sparse_super: Save space on large filesystem by creating fewer superblock backup copies.

-R stride=size

Configure filesystem for a RAID array. Set stride size to size blocks per stripe.

-S

Write only superblock and group descriptors; suppress writing of inode table and block and inode bitmaps. Useful only when attempting to salvage damaged systems.

-T use

Set bytes-per-inode based on the intended use of the filesystem. Supported filesystem types are:

news: Four kilobytes per inode.
largefile: One megabyte per inode.
largefile4: Four megabytes per inode.

-V

Specify a text string id that describes the application to be written into the volume header.

mkfifo

mkfifo [option] names

Make one or more named pipes (FIFOs) with the specified names.

Options

-m mode, --mode=mode: Set permission mode. Default is 666 with the bits in the umask subtracted.
--help: Print help information and exit.
--version: Print version information and exit.

mkfs

mkfs [options] [fs-options] filesys [blocks]

System administration command. Construct a filesystem on a device (such as a hard disk partition). filesys is either the name of the device or the mountpoint. mkfs is actually a frontend that invokes the appropriate version of mkfs according to a filesystem type specified by the -t option. For example, a Linux Second Extended Filesystem uses mkfs.ext2 (which is the same as mke2fs); MS-DOS filesystems use mkfs.msdos. fs-options are options specific to the filesystem type. blocks is the size of the filesystem in 1024-byte blocks.

Options

-V: Produce verbose output, including all commands executed to create the specific filesystem.
-t fs-type: Tells mkfs what type of filesystem to construct.

Filesystem-specific options

These options must follow generic options and cannot be combined with them. Most filesystem builders support these three options:

-c: Check for bad blocks on the device before building the filesystem.
-l file: Read the file file for the list of bad blocks on the device.
-v: Produce verbose ouput.

mkfs.ext3

mkfs.ext3 [options] device size

Create a journaling ext3 filesystem. Options are identical to mke2fs. See mkfs.

mkfs.minix

mkfs.minix [options] device size

System administration command. Create a MINIX filesystem. See mkfs.

mkisofs

mkisofs [options] -o file pathspecs

Generate an ISO9660/Joliet/HFS filesystem for writing to a CD with a utility such as cdrecord. (HFS is the native Macintosh Hierarchical File System.) mkisofs takes a snapshot of a directory tree and generates a binary image that corresponds to an ISO9660 or HFS filesystem when it is written to a block device. Each specified pathspec describes the path of a directory tree to be copied into the ISO9660 filesystem; if multiple paths are specified, the files in all the paths are merged to form the image.

Options

-A id, -appid id

-abstract file

Specify the abstract filename. Overrides an ABST=file entry in .mkisofsrc.

-allow-lowercase

Allow ISO9660 filenames to be lowercase. Violates the ISO9660 standard.

-allow-multidot

Allow more than one dot in ISO9660 filenames. Violates the ISO9660 standard.

-b image

Specify the path and filename of the boot image to be used for making a bootable CD based on the El Torito specification.

-B sun-images

Specify a comma-separated list of boot images needed to make a bootable CD for a Sun Sparc system.

-biblio file

Specify bibliographic filename. Overrides a BIBLIO=file entry in .mkisofsrc.

-boot-info-table

Specify that a 56-byte table with information on the CD layout is to be patched in at offset 8 of the boot file. If specified, the table is patched into the source boot file, so make a copy if the file isn't recreatable.

-boot-load-seg addr

Specify the load segment address of the boot image for a no-emulation El Torito CD.

-boot-load-size size

Specify the number of virtual 512-byte sectors to load in no-emulation mode. The default is to load the entire boot file. The number may need to be a multiple of 4 to prevent problems with some BIOSes.

-c catalog

Specify the path, relative to the source pathspec, and the filename of the boot catalog for an El Torito bootable CD. Required for making a bootable CD.

-C last-start,next-start

Required for creating a CDExtra or a second or higher-level session for a multisession CD. last-start is the first sector number in the last session on the disk, and next-start is the first sector number for the new session. Use the command:

cdrecord -msinfo

to get the values. Use -C with -M to create an image that is a continuation of the previous session; without -M, create an image for a second session on a CDExtra (a multisession CD with audio data in the first session and an ISO9660 filesystem image in the second).

-[no-]cache-inodes

Cache [do not cache] inode and device numbers to find hard links to files. The default on Linux is to cache. Use -no-cache-inodes for filesystems that do not have unique inode numbers.

-check-oldnames

Check all filenames imported from old sessions for mkisofs compliance with ISO9660 file-naming rules. If not specified, check only those files with names longer than 31 characters.

-check-session file

Check all old sessions for mkisofs compliance with ISO9660 file-naming rules. This option is the equivalent of:

-M file -C 0,0 -check-oldnames

where file is the pathname or SCSI device specifier that would be specified with -M.

-copyright file

Specify the name of the file that contains the copyright information. Overrides a COPY=file entry in .mkisofsrc.

-d

Omit trailing period from files that do not have one. Violates the ISO9660 standard, but works on many systems.

-D

Do not use deep directory relocation. Violates the ISO9660 standard, but works on many systems.

-dir-mode mode

Specify the mode for directories used to create the image. Automatically enables the Rock Ridge extensions.

-eltorito-alt-boot

Start with a new set of El Torito boot parameters. Allows putting more than one El Torito boot image on a CD (maximum is 63).

-exclude-list file

Check filenames against the globs contained in the specified file and exclude any that match.

-f

Follow symbolic links when generating the filesystem.

-file-mode mode

Specify the mode for files used to create the image. Automatically enables the Rock Ridge extensions.

-force-rr

Do not use automatic Rock Ridge detection for the previous session.

-G image

Specify the path and filename of the generic boot image for making a generic bootable CD.

-gid gid

Set the group ID to gid for the source files. Automatically enables the Rock Ridge extensions.

-graft-points

Allow the use of graft points for filenames, which permits paths to be grafted at locations other than the root directory. -graft-points checks all filenames for graft points and divides the filename at the first unescaped equals sign (=).

-gui

Switch the behavior for a GUI. Currently, the only effect is to make the output more verbose.

-hard-disk-boot

Specify that the boot image to be used to create an El Torito bootable CD is a hard disk image and must begin with a master boot record containing a single partition.

-hidden glob

Set the hidden (existence) ISO9660 directory attribute for paths or filenames matching the shell-style pattern glob. To match a directory, the path must not end with a trailing /.

-hidden-list file

Specify a file containing a list of globs that are to be hidden with -hidden.

-hide glob

Find paths or files that match the shell-style pattern glob and hide them from being seen on the ISO9660 or Rock Ridge directory. The files are still included in the image file. If the pattern matches a directory, the contents of the directory are hidden. To match a directory, the path must not end with a trailing /. Use with the -hide-joliet option.

-hide-joliet glob

Hide paths or files that match the shell-style pattern glob so they will not be seen in the Joliet directory. If the pattern matches a directory, the contents of the directory are hidden. To match a directory, the path must not end with a trailing /. Should be used with -hide.

-hide-joliet-list file

Specify a file containing a list of globs to be hidden with -hide-joliet.

-hide-joliet-trans-tbl

Hide the TRANS.TBL files from the Joliet tree.

-hide-list file

Specify a file containing a list of globs to be hidden with -hide.

-hide-rr-moved

Rename the directory RR_MOVED to .rr_moved to hide it as much as possible from the Rock Ridge directory tree. Use the -D option to omit the file entirely.

-input-charset charset

Specify the character set for characters used in local filenames. Specify help in place of a charset for a list of valid character sets.

-iso-level level

Set the ISO9660 conformance level. Possible values are:

1: Filenames are restricted to 8.3 characters and files may have only one section.
2: Files may have only one section.
3: No restrictions.

-J

Generate Joliet directory records in addition to regular ISO9660 filenames.

-jcharset charset

The equivalent of -input-charset -J.

-l

Allow full 31-character filenames instead of restricting them to the MS-DOS-compatible 8.3 format.

-L

Allow ISO9660 filenames to begin with a period.

-log-file file

Send all messages to the specified log file.

-m glob

Exclude files matching the shell-style pattern glob.

-M path

Specify the path to an existing ISO9660 image to be merged. path can also be a SCSI device specified in the same syntax as cdrecord's dev= parameter. May be used only with -C.

-max-iso9660-filenames

Allow up to 37 characters in ISO9660 filenames. Forces -N. Violates the ISO9660 standard.

-N

Omit version numbers from ISO9660 filenames. Violates the ISO9660 standard. Use with caution.

-new-dir-mode mode

Specify the mode to use for new directories in the image. The default is 0555.

-nobak, -no-bak

Do not include backup files on the ISO9660 filesystem.

-no-boot

Mark the El Torito CD to be created as not bootable.

-no-emul-boot

Specify that the boot image for creating an El Torito bootable CD is a no-emulation image.

-no-iso-translate

Do not translate the # and ~ characters. Violates the ISO9660 standard.

-no-rr

Do not use Rock Ridge attributes from previous sessions.

-no-split-symlink-components

Do not split symlink components.

-no-split-symlink-fields

Do not split symlink fields.

-o file

Specify the filename of the output ISO9660 filesystem image.

-output-charset charset

Specify the output character set for Rock Ridge filenames. The default is the input character set.

-p prepid

Specify a text string of up to 128 characters describing the preparer of the CD. Overrides a PREP= parameter set in the file .mkisofsrc.

-P pubid

Specify a text string of up to 128 characters describing the publisher of the CD to be written to the volume header. Overrides a PUBL= parameter set in .mkisofsrc.

-[no -]pad

Pad [do not pad] the ISO9660 filesystem by 16 sectors (32KB). If the resulting size is not a multiple of 16 sectors, add sectors until it is. The default is -pad.

-path-list file

Specify a file that contains a list of pathspec directories and filenames to add to the ISO9660 filesystem. Note that at least one pathspec must be given on the command line.

-print-size

Print estimated filesystem size and exit.

-quiet

Run in quiet mode; do not display progress output.

-r

Like -R, but set UID and GID to zero, set all file read bits to write, and turn off all file write bits. If any execute bit is set for a file, set all execute bits; if any search bit is set for a directory, set all search bits; if any special mode bits are set, clear them.

-R

Generate SUSP (System Use Sharing Protocol) and Rock Ridge records using the Rock Ridge protocol.

-relaxed-filenames

Allow ISO9660 filenames to include seven-digit ASCII characters except lowercase characters. Violates the ISO9660 standard.

-sort file

Sort file locations according to the rules in the specified file, which contains pairs of filenames and weights, with one space or tab between them. A higher weight puts the file closer to the beginning of the media.

-sysid id

Specify the system ID. Overrides a SYSI= parameter set in the file .mkisofsrc.

-T

Generate the file TRANS.TBL in each directory for establishing the correct filenames on non-Rock Ridge-capable systems.

-table-name table

Use table as the translation table name instead of TRANS.TBL. Implies -T. For a multisession image, the table name must be the same as the previous session.

-U

Allow untranslated filenames. Violates the ISO9660 standard. Forces the options -d, -l, -L, -n, -relaxed-filenames, -allow-lowercase, -allow-multidot, -no-iso-translate. Use with extreme caution.

-ucs-level num

Set the Unicode conformance level to the specified number, which can be between 1 and 3 (default is 3).

-use-fileversion

Use file version numbers from the filesystem. The version number is a string from 1 to 32767. The default is to set a version of 1.

-v

Run in verbose mode. Specify twice to run even more verbosely.

-V volid

Specify the volume ID (volume name or label) to be written to the master block. Overrides a VOLI= parameter specified in the file .mkisofsrc.

-volset id

Specify the volume set ID. Overrides a VOLS= parameter specified in .mkisofsrc.

-volset-seqno num

Set the volume set sequence number to num. Must be specified after -volset-size.

-volset-size num

Set the volume set size (the number of CDs in a set) to num. Must be specified before -volset-seqno.

-x path

Exclude path from being written to the CD, where path is the complete pathname derived from the concatenation of the pathname from the command line and the path relative to this directory. May be specified more than once to exclude multiple paths.

HFS options

-apple: Create an ISO9660 CD with Apple's extensions.
-auto file: Set file as the Autostart file to make the HFS CD use the QuickTime 2.0 Autostart feature. file must be the name of an application or document at the top level of the CD and must be less than 12 characters long.
-boot-hfs-file file: Install file as the driver file that may make the CD bootable on a Macintosh.
-cluster-size size: Specify the size in bytes of a cluster or allocation units of PC Exchange files. Implies the use of --exchange.
-hfs: Create a hybrid ISO9660/HFS CD. Use with -map, -magic, and/or the various --HFS options.
-hfs-bless folder: "Bless" the specified directory (folder), specified as the full pathname as mkisofs. This is usually the System Folder and is used in creating HFS bootable CDs. The pathname must be in quotes if it contains spaces.
-hfs-creator creator: Set the four-character default creator for all files.
-hfs-type type: Set the four-character default type for all files.
-hfs-unlock: Leave the HFS volume unlocked so other applications can modify it. The default is to lock the volume.
-hfs-volid id: Specify the volume name for the HFS partition. This name is assigned to the CD on a Macintosh and replaces the ID set with the -V option.
-hide-hfs glob: Hide files or directories matching the shell-style pattern glob from the HFS volume, although they still exist in the ISO9660 and/or Joliet directory. May be specified multiple times.
-hide-hfs-list file: The specified file contains a list of globs to be hidden.
-input-hfs-charset charset: Specify the input character set used for HFS filenames when used with the -mac-name option. The default is cp10000 (Mac Roman).
-mac-name: Use the HFS filename as the starting point for the ISO9660, Joliet, and Rock Ridge filenames.
-magic file: Use the specified magic file to set a file's creator and type information based on the file's magic number, which is usually the first few bytes of the file. The magic file contains entries consisting of four tab-separated columns specifying the byte offset, type, test, and a message.
-map file: Use the specified mapping file to set a file's creator and type information based on the filename extension. Only files that are not known Apple or Unix file types need to be mapped. The mapping file consists of five-column entries specifying the extension, file translation, creator, type, and a comment. Creator and type are both four-letter strings.
-no-desktop: Do not create empty Desktop files. The default is to create such files.
-output-hfs-charset charset: Specify the output character set used for HFS filenames. Defaults to the input character set.
-part: Generate an HFS partition table. The default is not to generate the table.
-probe: Search the contents of files for known Apple or Unix file types.
--format: Look for Macintosh files of the specified file format type. The valid formats are cap (Apple/Unix File System (AUFS) CAP files), netatalk, double, ethershare, ushare, exchange, sgi, xinet, macbin, single, dave, and sfm.

mklost+found

mklost+found

System administration command. Create a lost+found directory in the current working directory. Intended for Linux Second Extended Filesystems.

mknod

mknod [options] name type [major minor]

Create a special file (a file that can send or receive data). Special files can be character files (read one character at a time), block files (read several characters at a time), or FIFO pipes (see mkfifo).

To choose which type of device to create, use one of the arguments:

p: Create a FIFO file (named pipe). You do not need to specify the major and minor device numbers.
b: Create a block file. You must specify the major and minor device numbers the file represents.
c or u: Create a character file. You must specify the major and minor device numbers the file represents.

Linux's /dev/MAKEDEV utility is useful for creating one or more devices of a given type in a single command.

Options

--help: Print usage information and exit.
-m mode, --mode=mode: Set the file mode of the device, as with chmod. The default mode is a=rw unless you have chosen other settings via umask.
--version: Print version information and exit.

mkpasswd

mkpasswd [options] [user]

Generate a new password for the specified user. The passwords produced are hard to guess and therefore more secure than passwords made up by actual people. Some operating systems distribute a different mkpasswd command, which regenerates the user password database; if your system has this version, check the manpage for instructions on how to use it.

If you do not specify a user, mkpasswd will display a new password. If you do specify a user, make sure that you have permission to set their password; this will usually mean being root.

Options

-l n: Generate a password that is n characters long. The default is 9.
-d n: Generate a password with at least n digits in it. The default is 2.
-c n: Generate a password with at least n lowercase letters in it. The default is 2.
-C n: Set the minimum number of uppercase letters in the password. The default is 2.
-s n: Generate a password with at least n special characters in it. The default is 1.
-p programname: Set the program used to actually set the password. If you do not choose one, the system will try to use yppasswd, or, if that is not installed, passwd.
-2: Choose characters in the password so that, on a QWERTY-style keyboard, they alternate between left and right hand keys. This makes it harder for someone to guess what the password is if they watch you type it, but can make automated attacks easier.
-v: Verbose mode; display the interaction between mkpasswd and the system as it sets the password.

mkraid

mkraid [options] devices

System administration command. Set up RAID array devices as defined in the /etc/raidtab configuration file. mkraid can be used to initialize a new array or upgrade older RAID device arrays for the new kernel. Initialization will destroy any data on the disk devices used to create the array.

Options

-c file, --configfile file: Use file instead of /etc/raidtab.
-f, --force: Initialize the devices used to create the RAID array even if they currently have data.
-h, --help: Print a usage message and then exit.
-o, --upgrade: Upgrade an older array to the current kernel's RAID version. Preserve data on the old array.
-V, --version: Print version information and then exit.

mkswap

mkswap [option] device [size]

System administration command. Create swap space on device. You may specify its size in blocks; each block is a page of about 4KB.

Option

-c: Check for bad blocks before creating the swap space.

mktemp

mktemp [options] template

Generate a unique temporary filename for use in a script. The filename is based on the specified template, which may be any filename with at least six Xs appended (e.g., /tmp/mytemp.XXXXXX). mktemp replaces the Xs with the current process number and/or a unique letter combination. The file is created with mode 0600 (unless -u is specified) and the filename is written to standard output.

Options

-d: Make a directory, not a file.
-q: Fail silently in case of error. Useful to prevent error output from being sent to standard error.
-u: Operate in "unsafe" mode and unlink the temporary file before mktemp exits. Use of this option is not recommended.

mlabel

mlabel [options] drive[label]

Label an MS-DOS filesystem (maximum of 11 characters). See mtools for more information.

Options

-c: Overwrite any existing labels.
-s: Show the existing label.
-n: Create a random serial number for the disk.
-N serialno: Choose a new serial number for the disk. It should be an 8-digit hexadecimal number with no spaces in it.

mmd

mmd [option] dirname

Create a directory on an MS-DOS filesystem. See mkdir and mtools for more information.

Option

-D clash-option

Specify the action to take if the specified directory name already exists. The possible clash options are as follows. (The primary name is the long name if it exists and the short name otherwise; the secondary name is the short name if a long name exists.)

a: Auto-rename the primary name.
A: Auto-rename the secondary name.
m: Ask the user what to do with the primary name.
M: Ask the user what to do with the secondary name.
o: Overwrite the primary name.
O: Overwrite the secondary name.
r: Rename the primary name, prompting the user for the name.
R: Rename the secondary name, prompting the user for the name.
s: Skip the primary name.
S: Skip the secondary name.

mmount

mmount drive [mount-arguments]

Mount an MS-DOS filesystem, passing the mount-arguments to mount. If no mount-arguments are specified, the device name is used. See mount and mtools for more information.

mmove

mmove [options] sourcefile targetfile
mmove [options] sourcefiles targetdir

Move or rename an MS-DOS file or directory within a single filesystem. If no drive letter is specified for the target file or directory, the source drive is assumed. If no drive letter is specified for either the source or the target, drive a: is assumed. See mv and mtools for more information.

Options

-D clash-option: Specify the action to take if the specified target file or directory already exists. See mmd for the possible clash options.
-v: Verbose; display names of the files or directories being moved.

modinfo

modinfo [options] object-file

System administration command. Print information about kernel module object-file. Information is read from tag names in the mod-info section of the module file. By default it will print the module's filename, description, author, license, and parameters.

Options

-a, --author: Print author information.
-d, --description: Print module description.
-fformat-string, --format format-string: Format output to match string. The format string is essentially a printf style string. Fields to be replaced are specified by a percent sign followed by a tag name in curly braces, e.g., %{author} and %{filename}. A line containing the field %{parm} will be repeated for each known module parameter. author, description, filename, licenses, and parm can also be represented by the shorter versions, %a, %d, %n, %l, and %p.
-h, --help: Print usage message, then exit.
-l, --license: Print module license information.
-n, --filename: Print the module's filename.
-p, --parameters: Print the module's typed parameters.
-V, --version: Print version number of the module.

modprobe

modprobe [options] [modules]

System administration command. With no options, attempt to load the specified module, as well as all modules on which it depends. If more than one module is specified, attempt to load further modules only if the previous module failed to load. When specifying a module, use only its name without its path or trailing .o.

Options

-a, --all: Load all listed modules, not just the first one.
-c, --showconfig: Print modprobe's current configuration.
-d, --debug: Print debugging information about module.
-h, --help: Print help message, then exit.
-k, --autoclean: Mark module to be removed when inactive by setting its autoclean flag. This option is passed on to insmod.
-l, --list: List modules. This option may be combined with -t to specify a type of module.
-n, --show: Don't load or remove modules; only show what would happen if modules were loaded or removed.
-q, --quiet: Suppress warnings from insmod when it fails to load a module. Continue processing other modules. This option is passed on to insmod.
-r, --remove: Remove the specified modules, as well as the modules on which they depend.
-s, --syslog: Send error messages to syslogd instead of to standard error. This option is passed on to insmod.
-t type, --type type: Load only a specific type of module. Consult /etc/modules.conf for the directories in which all modules of that type reside.
-v, --verbose: Print commands as they are executed.
-C file, --config file: Read additional configuration from file instead of /etc/modules.conf.
-V, --version: Print version, then exit.

Files

/etc/modules.conf: Information about modules: which ones depend on others, and which directories correspond to particular types of modules.
/sbin/insmod, /sbin/rmmod, /sbin/depmod: Programs that modprobe relies on.

more

more [options] [files]

Display the named files on a terminal, one screenful at a time. See less for an alternative to more.

Options

+num: Begin displaying at line number num.
-num number: Set screen size to number lines.
+/pattern: Begin displaying two lines before pattern.
-c: Repaint screen from top instead of scrolling.
-d: Display the prompt "Hit space to continue, Del to abort" in response to illegal commands; disable bell.
-f: Count logical rather than screen lines. Useful when long lines wrap past the width of the screen.
-l: Ignore form-feed (Ctrl-L) characters.
-p: Page through the file by clearing each window instead of scrolling. This is sometimes faster.
-s: Squeeze; display multiple blank lines as one.
-u: Suppress underline characters.

Commands

All commands in more are based on vi commands. You can specify a number before many commands to have them executed multiple times. For instance, 3:p causes more to skip back three files, the same as issuing :p three times. The optional number is indicated by num in the following list.

SPACE: Display next screen of text.
z: Display next num lines of text, and redefine a screenful to num lines. Default is one screenful.
RETURN: Display next num lines of text, and redefine a screenful to num lines. Default is one line.
d, ^D: Scroll num lines of text, and redefine scroll size to num lines. Default is one line.
q, Q, INTERRUPT: Quit.
s: Display next screen of text.
f: Skip forward two screens of text.
b, ^B: Skip backward one screen of text.
': Return to point where previous search began.
=: Print number of current line.
/pattern: Search for pattern, skipping to numth occurrence if an argument is specified.
n: Repeat last search, skipping to numth occurrence if an argument is specified.
!cmd, :!cmd: Invoke shell and execute cmd in it.
v: Invoke vi editor on the file at the current line.
^L: Redraw screen.
:n: Skip to next file.
:p: Skip to previous file.
:f: Print current filename and line number.
.: Reexecute previous command.

Examples

Page through file in "clear" mode, and display prompts:

more -cd file

Format doc to the screen, removing underlines:

nroff doc | more -u

View the manpage for the more command; begin at the first appearance of the word "scroll":

man more|more +/scroll

mount

mount [options] [[device] directory]

System administration command. Mount a file structure. The file structure on device is mounted on directory. If no device is specified, mount looks for an entry in /etc/fstab to find what device is associated with the given directory. The directory, which must already exist and should be empty, becomes the name of the root of the newly mounted file structure. If mount is invoked with no arguments, it displays the name of each mounted device, the directory on which it is mounted, its filesystem type, and any mount options associated with the device.

Options

-a

Mount all filesystems listed in /etc/fstab. Use -t to limit this to all filesystems of a particular type.

-f

Fake mount. Go through the motions of checking the device and directory, but do not actually mount the filesystem.

-h

When reporting on mounted filesystems, show filesystem labels for filesystems that have them.

-l

-n

Do not record the mount in /etc/mtab.

-o option

Qualify the mount with a mount option. Many filesystem types have their own options. The following are common to most filesystems:

async: Read input and output to the device asynchronously.
atime: Update inode access time for each access. This is the default behavior.
auto: Allow mounting with the -a option.
defaults: Use all options' default values (async, auto, dev, exec, nouser, rw, suid).
dev: Interpret any special devices that exist on the filesystem.
exec: Allow binaries to be executed.
_netdev: Filesystem is a network device requiring network access.
noatime: Do not update inode access time for each access.
noauto: Do not allow mounting via the -a option.
nodev: Do not interpret any special devices that exist on the filesystem.
noexec: Do not allow the execution of binaries on the filesystem.
nosuid: Do not acknowledge any suid or sgid bits.
nouser: Only privileged users will have access to the filesystem.
remount: Expect the filesystem to have already been mounted, and remount it.
ro: Allow read-only access to the filesystem.
rw: Allow read/write access to the filesystem.
suid: Acknowledge suid and sgid bits.
sync: Read input and output to the device synchronously.
user: Allow unprivileged users to mount or unmount the filesystem. The defaults on such a system will be nodev, noexec, and nosuid, unless otherwise specified.
users: Allow any user to mount or unmount the filesystem. The defaults on such a system will be nodev, noexec, and nosuid, unless otherwise specified.

-r

Mount filesystem read-only.

-s

Where possible, ignore mount options specified by -o that are not supported by the filesystem.

-t type

Specify the filesystem type. Possible values include adfs, affs, autofs, coda, cramfs, devpts, efs, ext2, ext3, hfs, hpfs, iso9660, jfs, msdos, ncpfs, nfs, ntfs, proc, qnx4, reiserfs, romfs, smbfs, sysv, tmpfs, udf, ufs, umsdos, vfat, xfs, and xiafs. The default type is iso9660. The type auto may also be used to set mount to autodetect the filesystem. When used with -a, this option can limit the types mounted. Use a comma-separated list to specify more than one type to mount, and prefix a type with no to exclude that type.

-v

Display mount information verbosely.

-w

Mount filesystem read/write. This is the default.

-F

When used with -a, fork a new process to mount each system.

-L label

Mount filesystem with the specified label.

-O option

Limit systems mounted with -a by its filesystem options. (As used with -o.) Use a comma-separated list to specify more than one option, and prefix an option with no to exclude filesystems with that option. Options -t and -O are cumulative.

-U uuid

Mount filesystem with the specified uuid.

-V

Print version, then exit.

Files

/etc/fstab: List of filesystems to be mounted and options to use when mounting them.
/etc/mtab: List of filesystems currently mounted and the options with which they were mounted.
/proc/partitions: Used to find filesystems by label and uuid.

mountd

rpc.mountd [options]

NFS/NIS command. NFS mount request server. mountd reads the file /etc/exports to determine which filesystems are available for mounting by which machines. It also provides information about which filesystems are mounted by which clients. See also nfsd.

Options

-d kind, --debug kind: Specify debugging facility. Accepted values for kind are general, call, auth, parse, and all.
-f file, --exports-file file: Read the export permissions from file instead of /etc/exports.
-h, --help: Print help message, then exit.
-n, --no-tcp: Use UDP for mounts.
-o n, --descriptors n: Allow no more than n open file descriptors. The default is 256.
-p n, --port n: Bind to specified port instead of accepting a port from portmapper.
-v, --version: Print the version number, then exit.
-F, --foreground: Run mountd in the foreground.
-N n, --no-nfs-version n: Do not offer NFS version n.
-V n, --nfs-version n: Explicity offer NFS version n.

Files

/etc/exports: Information about mount permissions.
/var/lib/nfs/rmtab: List of filesystems currently mounted by clients.

mpartition

mpartition [options] drive

Create the MS-DOS partition specified by drive; used mostly on proprietary Unix systems where fdisk is unavailable. See mtools for more information. When a partition is being created, the default is for the number of sectors and heads and the length to be automatically determined, but they can also be specified as options.

Options

-a: Activate the partition, making it the bootable partition.
-b offset: The starting offset of the partition to be created, in sectors. The default is the start of the disk (partition 1) or immediately after the end of the previous partition.
-B bootsector: Read the template master boot record from the file specified by bootsector. Can be specified with -I.
-c: Create the partition.
-d: Deactivate the partition, making it nonbootable.
-f: Allow overriding of safeguards that perform consistency checking before any change is made to a partition. Can be specified with any operation that modifies the partition table.
-h heads: The number of heads for a partition being created.
-I: Initialize the partition table and remove all partitions.
-l length: The size of the partition to be created, in sectors.
-p: Print a command line to re-create the partition. With -v, print the current partition table.
-r: Remove the partition.
-s sectors: The number of sectors per track of the partition to be created.
-t cylinders: The number of cylinders of the partition to be created.
-v: With -p, print the current partition table; otherwise, for commands that modify the partition table, print it after it has been modified.
-vv: Print a hexadecimal dump of the partition table when reading and writing it.

mpg123

mpg123 [options] file

Command-line MP3 player. See mpg321.

mpg321

mpg321 [options] file
mpg123 [options] file

Command-line MP3 players, often used as backends for GUI music players. The files played may be local files or URLs. mpg321 and mpg123 behave the same way, except that mpg123 lacks the option --skip-printing-frames.

Options

-o devicetype: Name the type of audio device you are using. Valid types are oss (Open Sound System), sun (Sun audio system), alsa (Advanced Linux Sound Architecture), alsa09 (ALSA, version 0.9), esd (Enlightened Sound Daemon), and arts (Analog Real-Time Synthesizer).
-a, --audiodevice device: Name the actual device (e.g., /dev/sound/dsp1) you are using. This option is ignored if you have chosen -o arts. For esd running on remote systems, you must specify the host, and for alsa, you must specify the card and device (default is 0:0).
-g, --gain n: Set the volume (gain) to an integer between 1 and 100.
-k, --skip n: Do not play the first n frames of the file or stream.
-n, --frames n: Play only the first n frames of the file or stream.
-@, --list filename: Specify a playlist file. The format of filename is just a list of filenames, one file per line, to be played.
-z, --shuffle: Shuffle the files in the playlist and any files supplied on the command line, and play the list once. Each file will be played once.
-Z, --random: Each time one file is finished playing, choose a new file at random. Files may be played more than once, and mpg321 will continue playing songs at random until it is stopped.
-v, --verbose: Verbose mode. Display additional information about the file, including ID3 tags and time played/time remaining.
-s, --stdout: Mostly useful for developers, this option uses stdout instead of an audio device for its output. The output is 16-bit PCM, little-endian data.
-w, --wav filename: Instead of playing the song, write the output to the .wav file you specify. Choosing - as the filename sends the WAV data to stdout. This option is usually used with the --cdr option.
--cdr filename: Write to a CDR file. Choosing - as the filename sends the data to stdout.
--au filename: Instead of playing the file, write the output to the .au file you specify. Choosing - as the filename sends the data to stdout.
-t, --test: Test mode. Do not play or write any data.
-q, --quiet: Quiet mode. This still plays the file, but does not display any data about the file or about mpg321.
-R: Operate in "remote control" mode, allowing seek and pause. This option is useful almost exclusively for developers of graphical frontends for mpg321.
--stereo: Play in stereo. If audio is mono, send two identical streams as stereo output.
--aggressive: Aggressive mode takes a higher priority in the system if possible. It requires root access because it can preempt processes owned by other users.
--skip-printing-frames n: Save CPU cycles by displaying a status update only once every n frames. This option is not available in mpg123.
--help, --longhelp: Display usage information.
-V, --version: Display the version of mpg321 and then quit.

mrd

mrd [option] directory

Delete an MS-DOS directory. The directory should be empty. To delete a full directory and its contents, use mdeltree. See rmdir and mtools for more information.

Option

-v: Operate in verbose mode, displaying each directory as it is deleted.

mren

mren [options] file name

Rename an MS-DOS file. See rename and mtools for more information.

Options

-D clash-option: Specify the action to take if the specified new name already exists. See mmd for the possible clash options.
-v: Operate verbosely, showing the names of files and directories as they are renamed.
-V: Print version information and exit.

mshowfat

mshowfat file

Display the FAT clusters associated with a file on an MS-DOS system. See mtools for more information.

mt [option] operation [count]

Control a magnetic tape drive used to back up or restore system data. The operation argument determines what action will be taken, and unless the -f or --file option is used, the action is applied to the default tape drive named in the TAPE environment variable. The count argument determines how many times the operation is to be repeated. If not specified, it defaults to 1.

Options

-f, --file=device: Name the tape device to use. This may be a local device, character special file (see mknod), or a remote device, named as host:/path/to/drive or user@host:path/to/drive.
--rsh-command=command: Choose a different command to use when connecting to a remote drive. The default is set in MT_RSH, and is normally either ssh or rsh.
-V, --version: Print version number and exit.

Operations

mt can perform the following operations on tape drives. Operations applicable only to SCSI tape drives are marked as such.

eof, weof n: Write n end-of-file (EOF) notations at the current location on the tape.
fsf n: Move forward n files, positioning the tape at the first block of the next file.
bsf n: Move backward n files, positioning the tape at the first block of the previous file.
fsr n: Move forward n records.
bsr n: Move backward n records.
bsfm n: Move backward n file marks, to a position on side of the file mark closer to the beginning of the tape.
fsfm n: Move forward n file marks, to a position on side of the file mark closer to the beginning of the tape.
asf n: Move to file number n on the tape. This is the same as rewinding the tape and moving forward n spaces with fsf.
eom: Move to the end of recording on the tape. Usually used when preparing to record new data onto the tape.
rewind: Return to the beginning of the tape.
offline, rewoffl: Rewind and unload the tape (if drive supports unload).
status: Display the status of the tape drive.
retension: Used when the tape has become loosely wound, usually because it has been dropped, shaken, or transported. Rewinds the tape, moves forward to the end of the tape, then rewinds again.
erase: Erase the tape.
fss n: SCSI drives only. Move forward n set marks.
bss n: SCSI drives only. Move backward n set marks.
wset n: SCSI drives only. Write n set marks at current position.
eod, seod: Move to the end of valid data on the tape. Similar to eom, but used with streamer tapes.
setblk n: SCSI drives only. Set the block size to n bytes per record.
setdensity n: SCSI drives only. Set the data density for your tape drive to n. The appropriate value should be in the tape or tape drive documentation. For more information, see the densities operation.
drvbuffer n: SCSI drives only. Set the buffer value. For no buffer, choose 0, and for normal buffering, choose 1. Other values may have different effects depending on the drive.
stoptions n: SCSI drives only. Set the driver bits for the device; items are added as with chmod. 1 is for write buffering, 2 for asynchronous writing, 4 for read-ahead, and 8 for debugging output.
stwrthreshold n: SCSI drives only. Set the write threshold for the tape drive to n kilobytes. This value may not be higher than the driver buffer value.
seek n: SCSI drives only. Seek to block n on the tape.
tell: SCSI drives only. Tell the number of the current block on the tape.
densities: SCSI tapes only. Display information about data densities on stdout.
datacompression [n]: Works on some SCSI-2 DAT tapes only. If n is 0, turn data compression off. If n is 1, display the compression status. Other values turn compression on.

mtools

command [options] [arguments]

A collection of tools for working with MS-DOS files and filesystems, especially for accessing files on floppy disks without mounting them as Unix filesystems. The various commands are mattrib, mbadblocks, mcat, mcd, mcopy, mdel, mdeltree, mdir, mdu, mformat, minfo, mlabel, mmd, mmount, mmove, mpartition, mrd, mren, mshowfat, mtoolstest, mtype, and mzip.

For the purposes of mtools, all MS-DOS file names begin with a drive letter and colon, followed by the path. mtools accepts both / and \ for directory separators. For example, an MS-DOS file might be referred to as a:/directory/subdirectory/file.txt. If you use the backslash or any standard Unix wildcards or special characters, put the filename in quotation marks.

FAT filesystem filenames are normally a maximum of eight characters long with a three-letter extension, and are not case-sensitive. Even in the more recent VFAT system, which does preserve case sensitivity, two files with the same letters in their names, regardless of case, cannot coexist. Unix filenames that are too long, that use reserved characters (; + = [ ] ' , \ " * \ \ < > / ? : or |), or that conflict with MS-DOS devices (PRN, for example) are converted to VFAT names. This means replacing reserved characters with an underscore (_) and shortening files as needed, replacing several characters with a single tilde (~).

mtoolstest

mtoolstest

Display the configuration for mtools. See mtools for more information.

mtype

mtype [options] files

Display the contents of an MS-DOS file, as with the MS-DOS command type. See mtools for more information.

Options

-s: Strip the high bit from the data.
-t: View as a text file, changing carriage return/line feeds to line feeds.

mv [option] sources target

Move or rename files and directories. The source (first column) and target (second column) determine the result (third column):

Source	Target	Result
File	name (nonexistent)	Rename file to name.
File	Existing file	Overwrite existing file with source file.
Directory	name (nonexistent)	Rename directory to name.
Directory	Existing directory	Move directory to be a subdirectory of existing directory.
One or more files	Existing directory	Move files to directory.

Options

-b, --backup

Back up files before removing.

-f, --force

Force the move, even if target file exists; suppress messages about restricted access modes.

--help

Query user before removing files.

-i, --interactive

-u, --update

Do not remove a file or link if its modification date is the same as or newer than that of its replacement.

-v, --verbose

Print the name of each file before moving it.

--version

Override the SIMPLE_BACKUP_SUFFIX environment variable, which determines the suffix used for making simple backup files. If the suffix is not set either way, the default is a tilde (~).

-S suffix, --suffix=suffix

-V value, --version-control=value

Override the VERSION_CONTROL environment variable, which determines the type of backups made. The acceptable values for version control are:

t, numbered: Always make numbered backups.
nil, existing: Make numbered backups of files that already have them, simple backups of the others. This is the default.
never, simple: Always make simple backups.

mzip

mzip [options] [drive:]

Set modes or eject an MS-DOS-formatted ZIP or JAZ disk. See mtools for information about handling MS-DOS filesystems. Unix-formatted ZIP and JAZ drives can be handled as you would a floppy or other removable media, using the mount and umount commands.

Note that a ZIP drive is usually referred to as drive Z:, and a JAZ drive as drive J:.

Options

-e: Eject the disk.
-f: Force eject (even if the disk is mounted). Must be used in combination with -e.
-r: Put disk into read-only mode.
-w: Put disk into read/write mode.
-P: Prevent writing to the disk without a password.
-x: Prevent read or write access to the disk without a password.
-u: Make the disk writable, but restore write protection on eject.
-q: Query and display the disk status.

named

named [options]

TCP/IP command. Internet domain name server. named is used by resolver libraries to provide access to the Internet distributed naming database. With no arguments, named reads /etc/named.conf for any initial data and listens for queries on a privileged port. See RFC 1034 and RFC 1035 for more details.

There are several named binaries available at different Linux archives, displaying various behaviors. Here we describe named as provided by Internet Software Consortium's Berkeley Internet Name Domain (BIND) version 9.2.x.

Options

-c file: Read configuration information from file instead of /etc/named.conf.
-d debuglevel: Print debugging information. debuglevel is a number indicating the level of messages printed.
-f: Run named in the foreground.
-g: Run named in the foreground and send all log messages to standard error.
-n n: Specify the number of processors in a multiprocessor system. Normally named can autodetect the number of CPUs.
-p port: Use port as the port number. Default is 53.
-t dir: Change root to specified directory after reading command arguments but before reading the configuration file. Useful only when running with option -u.
-u user: Set the user ID to user after completing any privileged operations.
-v: Print version, then exit.

File

/etc/named.conf: Read when named starts up.

namei

namei [options] pathname [pathname . . .]

Follow a pathname until a terminal point is found (e.g., a file, directory, char device, etc.). If namei finds a symbolic link, it shows the link and starts following it, indenting the output to show the context. namei prints an informative message when the maximum number of symbolic links this system can have has been exceeded.

Options

-m: Show mode bits of each file type in the style of ls (e.g.,"rwxr-xr-x").
-x: Show mountpoint directories with a D rather than a d.

File type characters

For each line of output, namei prints the following characters to identify the file types found:

-: A regular file.
?: An error of some kind.
b: A block device.
c: A character device.
d: A directory.
f:: The pathname namei is currently trying to resolve.
l: A symbolic link (both the link and its contents are output).
s: A socket.

nameif

nameif [options] [name macaddress]

System administration command. Assign an interface name to a network device specified by macaddress, the unique serial number that identifies a network card. If no name and macaddress are given, nameif will attempt to read addresses from the configuration file /etc/mactab. Each line of the configuration file should contain either a comment beginning with # or an interface name and MAC address.

Options

-c filename: Read interface names and MAC addresses from filename instead of /etc/mactab.
-s: Send any error messages to syslog.

File

/proc/ksyms: List of interface names and MAC addresses used to rename interfaces.

netstat

netstat [options]

TCP/IP command. Show network status. Print information on active sockets, routing tables, interfaces, masquerade connections, or multicast memberships. By default, netstat lists open sockets.

Options

The first five options( -g, -i, -r, -s, and -M) determine what kind of information netstat should display.

-g, --groups: Show multicast group memberships.
-i, --interface[=name]: Show all network interfaces, or just the interface specified by name.
-r, --route: Show kernel routing tables.
-s, --statistics: Show statistics for each protocol.
-M, --masquerade: Show masqueraded connections.
-a, --all: Show all entries.
-c, --continuous: Display information continuously, refreshing once every second.
-e, --extend: Increase level of detail in reports. Use twice for maximum detail.
-l, --listening: Show only listening sockets.
-n, --numeric: Show network addresses, ports, and users as numbers.
--numeric-hosts: Show host addresses as numbers, but resolve others.
--numeric-ports: Show ports as numbers, but resolve others.
--numeric-users: Show user ID numbers for users, but resolve others.
-o, --timers: Include information on network timers.
-p, --program: Show the process ID and name of the program owning the socket.
--protocol=family: Show connections only for the specified address family. Accepted values are inet, unix, ipx, ax25, netrom, and ddp.
-t, --tcp: Limit report to information on TCP sockets.
-u, --udp: Limit report to information on UDP sockets.
-v, --verbose: Verbose mode.
-w, --raw: Limit report to information on raw sockets.
-C: Print routing information from the route cache.
-F: Print routing information from the forward information database (FIB). This is the default.
-N, --symbolic: Where possible, print symbolic host, port, or user names instead of numerical representatitons. This is the default behavior.

newaliases

newaliases

Rebuild the mail aliases database, /etc/aliases, after a change. Return 0 on success, or a number greater than 0 if there was an error. newaliases must be run whenever /etc/aliases has been changed for the change to take effect. Identical to sendmail -bi.

newgrp

newgrp [group]

Change user's group ID to the specified group. If no group is specified, change to the user's login group. The new group is then used for checking permissions.

newusers

newusers file

System administration command. Create or update system users from entries in file. Each line in file has the same format as an entry in /etc/passwd except that passwords are unencrypted, and group IDs can be given as a name or number. During an update, the password age field is ignored if the user already exists in the /etc/shadow password file. If a group name or ID does not already exist, it will be created. If a home directory does not exist, it will be created.

nfsd

rpc.nfsd [option] n

System administration command. Launch n kernel threads for the Network File System (NFS) kernel module. The threads will handle client filesystem requests. By default only one thread is launched. Most systems require eight or more, depending on the number of NFS clients using the system. Use nfsstat to check NFS performance.

Option

-p port: Listen for NFS requests on port instead of the default port 2049.

nfsstat

nfsstat [options]

System administration command. Print statistics on NFS and remote procedure call (RPC) activity for both clients and server.

Options

-c

Display only client-side statistics.

-n

Display only NFS statistics.

-r

Display only RPC statistics.

-s

Display only server-side statistics.

-o facility

Only display statistics for the specified facility. The following are valid values for facility:

fh: Server file handle cache.
net: Network layer statistics.
nfs: Same as -n.
rc: Server request reply cache.
rpc: Same as -r.

nice

nice [option] [command [arguments]]

Execute a command (with its arguments) with lower priority (i.e., be "nice" to other users). With no arguments, nice prints the default scheduling priority (niceness). If nice is a child process, it prints the parent process's scheduling priority. Niceness has a range of -20 (highest priority) to 19 (lowest priority).

Options

--help: Print a help message and then exit.
-n adjustment, -adjustment, --adjustment=adjustment: Run command with niceness incremented by adjustment (1-19); default is 10. A privileged user can raise priority by specifying a negative adjustment (e.g., -5).
--version: Print version information and then exit.

nm [options] [objfiles]

Print the symbol table (name list) in alphabetical order for one or more object files. If no object files are specified, perform operations on a.out. Output includes each symbol's value, type, size, name, and so on. A key letter categorizing the symbol can also be displayed.

Options

-a, --debug-syms: Print debugger symbols.
--defined-only: Display only defined symbols.
-f format, --format=format: Specify output format (bsd, sysv, or posix). Default is bsd.
-g, --extern-only: Print external symbols only.
--help: Print help message, then exit.
-l, --line-numbers: Print source filenames and line numbers for each symbol from available debugging information.
-n, -v, --numeric-sort: Sort the external symbols by address.
-p, --no-sort: Don't sort the symbols at all.
-r, --reverse-sort: Sort in reverse, alphabetically or numerically.
-s, --print-armap: Include mappings stored by ar and ranlib when printing archive symbols.
--size-sort: Sort by size.
-t radix, --radix=radix: Use the specified radix for printing symbol values. Accepted values are d for decimal, o for octal, and x for hexadecimal.
--target=format: Specify an object code format other than the system default.
-u, --undefined-only: Report only the undefined symbols.
-A, -o, -print-file-name: Print input filenames before each symbol.
-C, --demangle[=style]: Translate low-level symbol names into readable versions. You may specify a style to use when demangling symbol names from a foreign compiler.
-D, --dynamic: Print dynamic, not normal, symbols. Useful only when working with dynamic objects (some kinds of shared libraries, for example).
-P, --portability: Same as -f posix.
-S, --print-size: Print the size of defined symbols.
-V, --version: Print nm's version number on standard error.

nohup

nohup command [arguments]
nohup option

Run the named command with its optional command arguments, continuing to run it even after you log out (make command immune to hangups; i.e., no hangup). Terminal output is appended to the file nohup.out by default. Modern shells preserve background commands by default; this command is necessary only in the original Bourne shell.

Options

--help: Print usage information and exit.
--version: Print version information and exit.

nslookup

nslookup [-option...] [host_to_find | -[server ]]

TCP/IP command. Query Internet domain name servers. nslookup is deprecated; its functionality is replaced by the dig and host commands. nslookup may not be included in some distributions.

nslookup has two modes: interactive and noninteractive. Interactive mode allows the user to query name servers for information about various hosts and domains or to print a list of hosts in a domain. It is entered either when no arguments are given (default name server will be used) or when the first argument is a hyphen and the second argument is the hostname or Internet address of a name server. Noninteractive mode is used to print just the name and requested information for a host or domain. It is used when the name of the host to be looked up is given as the first argument. Any of the keyword=value pairs listed under the interactive set command can be used as an option on the command line by prefacing the keyword with a -. The optional second argument specifies a name server.

Options

All of the options under the set interactive command can be entered on the command line, with the syntax -keyword[=value].

Interactive commands

exit: Exit nslookup.
finger [name] [>|>>filename]: Connect with finger server on current host, optionally creating or appending to filename.
help, ?: Print a brief summary of commands.
host [server]: Look up information for host using the current default server, or server if specified.
ls -[ahd] domain [>|>>filename]: List information available for domain, optionally creating or appending to filename. The -a option lists aliases of hosts in the domain. -h lists CPU and operating system information for the domain. -d lists all contents of a zone transfer.
lserver domain: Change the default server to domain. Use the initial server to look up information about domain.
root: Change default server to the server for the root of the domain namespace.
server domain: Change the default server to domain. Use the current default server to look up information about domain.
set keyword[=value]

nsupdate

nsupdate [options] [filename]

System administration command. Interactively submit dynamic DNS update requests to a name server. Use nsupdate to add or remove records from a zone without manually editing the zone file. Commands may be entered interactively or read from filename. An update message is built from multiple commands, some establishing prerequisites, some adding or deleting resource records. Messages are executed as a single transaction. A blank line or the send command will send the current message. Lines beginning with a semicolon are treated as comments. For additional information on dynamic DNS updates, see RFC 2136.

Options

-d: Print additional tracing information usable for debugging.
-k keyfile: Read encrypted transaction signature key from keyfile. The key should be encrypted using the HMAC-MD5 algorithm. Keyfiles are generated by the dnssec-keygen command.
-v: Use TCP instead of UDP to send update requests.
-y keyname:secret: Generate transaction signature from specified keyname and secret.

Interactive commands

key keyname secret: Generate transaction signature from specified keyname and secret. This command overrides command-line options -k or -y.
local address [port]: Use local address and, if specified, port to send updates.
prereq nxdomain domain-name: Perform updates only if there are no preexisting records with the name domain-name.
prereq nxrset domain-name [class] type: Perform updates only if there are no preexisting records of the specified type and class for domain-name. When no class is given, IN is assumed.
prereq yxdomain domain-name: Perform updates only if there is a preexisting record with the name domain-name.
prereq nxrset domain-name [class] type [data.: Perform updates only if there is a preexisting record of the specified type and class for domain-name. If data is given, the RDATA of the specified resource must match it exactly. When no class is given, IN is assumed.
send: Send the current message. Same as entering a blank line.
server servername [port]: Update records on DS server servername instead of the master server listed in the MNAME field of the appropriate zone's SOA record.
show: Print all commands in current message.
update add domain-name [ttl] [class] type data: Add a resource record with the specified values.
update delete domain-name [ttl] [class] [type [data]]: Delete resource records for domain-name. The ttl field is always ignored, but if other fields are given, only delete records that match all criteria.
zone zonename: Apply updates to the specified zonename. If no zone command is given, nsupdate attempts to determine the correct zone based on other input.

objcopy

objcopy [options] infile [outfile]

Copy the contents of the input object file to another file, optionally changing the file format in the process (but not the endian-ness). If outfile is not specified, objcopy creates a temporary file and renames it to infile when the copy is complete, destroying the original input file. The GNU Binary File Descriptor (BFD) library is used to read and write the object files.

Options

--add-section section=file: Add a new section to the output object file with the specified section name and the contents taken from the specified file. Available only for formats that allow arbitrarily named sections.
--alt-machine-code=n: If the output architecture has alternate machine codes, use the nth code instead of the default.
-b n, --byte=n: Copy only every nth byte. Header data is not affected. The value of n can be from 0 to interleave-1, where interleave is specified by -i (default is 4). This option is useful for creating files to program ROM and is typically used with srec as the output format.
-B bfdarch, --binary-architecture=bfdarch: Set the output architecture to bfdarch (e.g., i386) for transforming a raw binary file into an object file. Otherwise, this option is ignored. After the conversion, your program can access data inside the created object file by referencing the special symbols _binary_objfile_start, _binary_objfile_end, and _binary_objfile_size.
--change-addresses=incr, --adjust-vma=incr: Change the VMA and LMA addresses of all sections, plus the start address, by adding incr. Changing section addresses is not supported by all object formats. Sections are not relocated.
--change-leading-char: For object formats that use a special character (such as an underscore) to begin symbols, change the leading character when converting between formats. If the character is the same in both formats, the option has no effect. Otherwise, it adds, removes, or changes the leading character as appropriate for the output format.
--change-section-address section{=|+|-}val, --adjust-section-vma section{=|+|-}val: Set or change the VMA and LMA addresses of the specified section. With =, set the section address to the specified value; otherwise, add or subtract the value to get the new address.
--change-section-lma section{=|+|-}val: Set or change the LMA address of the specified section. With =, set the section address to the specified value; otherwise, add or subtract the value to get the new address.
--change-section-vma section{=|+|-}val: Set or change the VMA address of the specified section. With =, set the section address to the specified value; otherwise, add or subtract the value to get the new address.
--change-start incr, --adjust-start incr: Add incr to the start address to get a new start address. Not supported by all object formats.
--change-warnings, --adjust-warnings: Issue a warning if the section specified in one of the options --change-section-address, --change-section-lma, or --change-section-vma does not exist.
--debugging: Convert debugging information if possible.
-F bfdname, --target=bfdname: Set the binary format for both input and output files to the binary file descriptor name bfdname. No format translation is done. Use the -h option for a list of supported formats for your system.
-g, --strip-debug: Do not copy debugging information.
-G symbol, --keep-global-symbol=symbol: Copy only the specified global symbol, making all other symbols local to the file. May be specified multiple times.
--gap-fill=val: Fill gaps between sections with the specified value; applies to the load address (LMA) of the sections.
-h, --help: Print help information, including a list of supported target object formats, then exit.
-i interleave, --interleave=interleave: Copy one out of every interleave bytes. Use -b to set the byte to copy (default is 4). This option is ignored if -b is not specified.
-I bfdname, --input-target=bfdname: Set the binary file format of the input file using its binary file descriptor name, bfdname.
-j section, --only-section=section: Copy only the specified section. May be specified multiple times.
-K symbol, --keep-symbol=symbol: Copy only the specified symbol from the source file. May be specified multiple times.
--keep-global-symbols=filename: Apply the option --keep-global-symbol to each symbol listed in the specified file. The file should have one symbol per line, with comments beginning with a hash mark (#). May be specified multiple times.
--keep-symbols=file: Apply the option --keep-symbol to each symbol listed in the specified file. The file should have one symbol per line, with comments beginning with a hash mark (#). May be specified multiple times.
-L symbol, --localize-symbol=symbol: Make the specified symbol local. May be specified multiple times.
--localize-symbols=filename: Apply the option --localize-symbol to each symbol listed in the specified file. The file should have one symbol per line, with comments beginning with a hash mark (#). May be specified multiple times.
-N symbol, --strip-symbol=symbol: Do not copy the specified symbol. May be specified multiple times.
--no-change-warnings, --no-adjust-warnings: Do not issue a warning even if the section specified in one of the options --change-section-address, --change-section-lma, or --change-section-vma does not exist.
-O bfdname, --output-target=bfdname: Set the binary file format of the output file using its binary file descriptor name, bfdname. The format srec generates S-records (printable ASCII versions of object files), and binary generates a raw binary file. Use -h for other available formats.
-p, --preserve-dates: Preserve the input file's access and modification dates in the output file.
--pad-to=addr: Pad the output file up to the load address. Use the fill value specified by --gap-fill (default is 0).
-R section, --remove-section=section: Do not copy any section with the specified name. May be specified multiple times.
--redefine-sym old=new: Change the name of the symbol old to new.
--remove-leading-char: If the first character of a global symbol is a special character (such as an underscore) used by the input object file format, remove it. Unlike --change-leading-char, this option always changes the symbol name when appropriate, regardless of the output object format.
--rename-section oldname=newname[,flags]: Rename a section from oldname to newname, optionally also changing the flags to flags.
-S, --strip-all: Do not copy relocation and symbol information.
--set-section-flags section=flags: Set flags for the specified section as a comma-separated string of flag names. Not all flags are meaningful for all object formats. The possible flags are alloc, code, contents, data, debug, load, noload, readonly, rom, and share.
--set-start=val: Set the start address of the new file to the specified value. Not supported by all object formats.
--srec-forceS3: Force all srec output records to be type S3 records.
--srec-len=ival: Set the maximum length of srec output records to the specified value. The length includes the address, data, and crc fields.
--strip-symbols=filename: Apply the option --strip-symbol to each symbol listed in the specified file. The file should have one symbol per line, with comments beginning with a hash mark (#). May be specified multiple times.
--strip-unneeded: Strip all symbols not needed for relocation processing.
-v, --verbose: Run in verbose mode, listing all object files modified; for archives, list all archive members.
-V, --version: Print version information and exit.
-W symbol, --weaken-symbol=symbol: Make the specified symbol weak. May be specified multiple times.
--weaken: Make all global symbols weak.
--weaken-symbols=filename: Apply the option --weaken-symbol to each symbol listed in the specified file. The file should have one symbol per line, with comments beginning with a hash mark (#). May be specified multiple times.
-x, --discard-all: Do not copy nonglobal symbols.
-X, --discard-locals: Do not copy compiler-generated local symbols (usually those starting with L or ..).

objdump

objdump [options] objfiles

Display information about one or more object files. If an archive is specified, objdump displays information on each object file in the archive. At least one of the options -a, -d, -D, -f, -g, -G, -h, -H, -p, -r, -S, -t, -T, -V, or -x must be given to tell objdump what information to show.

Options

-a, --archive-header: If any input files are archives, display the archive header information. The output includes the object file format of each archive member.
--adjust-vma=offset: Add offset to all section headers before dumping information. Useful if the section addresses do not correspond to the symbol table.
-b bfdname, --target=bfdname: Set the binary file format using its binary file descriptor name, bfdname. Use the -h option for a list of supported formats for your system.
-C [style], --demangle[=style]: Decode (demangle) low-level symbol names into user-level names, optionally specifying a mangling style. Removes any initial underscores and makes C++ function names readable.
-d, --disassemble: Display assembler mnemonic names for the machine instructions. Disassemble only sections that are expected to contain instructions.
-D, --disassemble-all: Disassemble all sections, not just those expected to contain instructions.
-EB, --endian=big
-EL, --endian=little: Specify whether the object files are big- or little-endian, for disassembling. Useful for disassembling formats such as S-records (printable ASCII versions of object files) that do not include that information.
-f, --file-header: Display overall header summary information.
--file-start-context: When using -S and displaying source code from a file that hasn't been displayed yet, include context from the start of the file.
-g, --debugging: Display debugging information.
-G, --stabs: Display any stabs (debugging symbol table entries) information, in addition to the contents of any sections requested.
-h, --section-header, --header: Display section header summary information.
-H, --help: Display help information and exit.
-i, --info: Display the architectures and object formats available on your system for use with -b or -m.
-j name, --section=name: Display information for section name.
-l, --line-numbers: Label the display with filename and source code line numbers corresponding to the object code or relocation entries shown. Use with -d, -D, or -r.
-m arch, --architecture=arch: Specify the architecture for disassembling object files. Useful when disassembling files such as S-records that do not include this information.
-M options, --disassembler-options=options: Pass target-specific information to the disassembler. Supported only on some targets.
--no-show-raw-insn: Do not show instructions in hexadecimal when disassembling. This is the default with --prefix-addresses.
-p, --private-headers: Display information specific to the object format. For some formats, no additional information is displayed.
--prefix-addresses: When disassembling, print the complete address on each line.
-r, --reloc: Display relocation entries. With -b or -D, the entries are intermixed with the disassembly.
-R, --dynamic-reloc: Print dynamic relocation entries. Meaningful only for dynamic objects such as certain types of shared libraries.
-s, --full-contents: Display the full contents of any requested sections.
-S, --source: Display source code intermixed with disassembly, if possible. Implies -d.
--show-raw-insn: When disassembling, show instructions in hexadecimal as well as symbolic form. This is the default except with --prefix-addresses.
--start-address=addr: Start displaying data at the specified address. Applies to -d, -r, and -s.
--stop-address=addr: Stop displaying data at the specified address. Applies to -d, -r, and -s.
-t, --syms: Print symbol table entries.
-T, --dynamic-syms: Print dynamic symbol table entries. Meaningful only for dynamic objects such as certain types of shared libraries.
-V, --version: Print version information and exit.
-w, --wide: Format lines for output devices wider than 80 characters, and do not truncate symbol table names.
-x, --all-header: Display all available header information. Equivalent to specifying -a -f -h -r -t.
-z, --disassemble-zeroes: Disassemble blocks of zeroes. The default is to skip such blocks.

od [options] [files]
od --traditional [file] [[+]offset [[+]label]]

Dump the specified files to standard output. The default is to dump in octal format, but other formats can be specified. With multiple files, concatenate them in the specified order. If no files are specified or file is -, read from standard input. With the second form, using the --traditional option, only one file can be specified.

Options

For the following options, see the later "Arguments" section for an explanation of the arguments bytes, size, and type. If no options are specified, the default is -A o -t d2 -w 16.

-a

Print as named characters. Same as -ta.

-Aradix, --address-radix=radix

Specify the radix (base) for the file offsets printed at the beginning of each output line. The possible values are:

d: Decimal.
n: None; do not print an offset.
o: Octal; the default.
x: Hexadecimal.

-b

Print as octal bytes. Same as -toC.

-c

Print as ASCII characters or backslash escapes. Same as -tc.

-d

Print as unsigned decimal shorts. Same as -tu2.

-f

Print as floating point. Same as -tfF.

-h

Print as hexadecimal shorts. Same as -tx2.

--help

Display a usage message and exit.

-i

Print as decimal shorts. Same as -td2.

-jbytes, --skip-bytes=bytes

Skip the specified number of input bytes before starting.

-l

Print as decimal longs. Same as -td4.

-Nbytes, --read-bytes=bytes

Format and print only the specified number of input bytes.

-o

Print as octal shorts. Same as -to2.

-sbytes, --strings[=bytes]

Output strings that are at least bytes ASCII graphic characters long (default 3 if bytes is not specified for --strings).

-ttype, --format=type

Format the output according to type, where type is a string of one or more of the characters listed in the "Arguments" section. If more than one type is specified, each output line is written once in each specified format. If a trailing z is appended to type, od appends any printable characters to the end of each output line.

--traditional

Accept arguments in the traditional form, which takes a single file specification with an optional offset and label as shown in the second form of the command. offset is an octal number indicating how many input bytes to skip over. label specifies an initial pseudo-address, which is printed in parentheses after any normal address. Both the offset and the label can begin with an optional plus sign (+), and can have a trailing decimal point (.) to force the offset to be interpreted as a decimal number and/or a trailing b to multiply the number of bytes skipped by offset by 512.

-v, --output-duplicates

Print all lines, including duplicates. By default, only the first of a series of identical lines is printed, and an asterisk is printed at the beginning of the following line to indicate that there were duplicates.

--version

Display version information and exit.

-wbytes, --width[=bytes]

Dump bytes input bytes to each output line. Defaults to 16 if this option is omitted. If --width is specified but bytes is omitted, the default is 32.

-x

Print as hexadecimal shorts. Same as -tx2.

Arguments

bytes

Specify a number of bytes. Treated as hexadecimal if it begins with 0x or 0X, as octal if it begins with 0, or as decimal otherwise. Append b to multiply by 512, k to multiply by 1024, or m to multiply by 10248576.

size

Specified as part of type to indicate how many bytes to use in interpreting each number. Types a and c do not take a size. For other types, size is a number. For type f, size can also be one of the following:

D: Double.
F: Float.
L: Long double.

For the remaining types (d, o, u, x), size can be one of the following in addition to a number:

C: Character.
I: Integer.
L: Long.
S: Short.

type

Specify the format type. The possible types are:

a: Named character.
c: ASCII character or backslash escape.
dsize: Signed decimal, with size bytes per integer.
fsize: Floating point, with size bytes per integer.
o: Octal, with size bytes per integer.
u: Unsigned decimal, with size bytes per integer.
x: Hexadecimal, with size bytes per integer.

openvt

openvt [options] [--] [command] [arguments]

Locate the first available virtual terminal (VT) and run command with any arguments given. If no command is specified, the shell $SHELL is started.

Options

--: Required before the command name to pass options to the command.
-c vt: Use the specified VT number instead of the first available. You must have write access to vt.
-l: Run the command as a login shell, prepending a dash (-) to the command name.
-s: Switch to the new VT when the command is started.
-u: Determine the owner of the current VT and log in as that user. You must be root to use this option, which is also suitable for calling by init. Don't use with -l.
-v: Verbose mode.
-w: Wait for the command to complete. If used with -s, switch back to the controlling terminal when the command is done.

passwd

passwd [user]

Create or change a password associated with a user name. Only the owner or a privileged user may change a password. Owners need not specify their user name.

paste

paste [options] files

Merge corresponding lines of one or more files into tab-separated vertical columns. See also cut, join, and pr.

Options

-: Replace a filename with the standard input.
-dchar, --delimiters=char: Separate columns with char instead of a tab. You can separate columns with different characters by supplying more than one char.
--help: Print a help message and then exit.
-s, --serial: Merge lines from one file at a time.
--version: Print version information and then exit.

Examples

Create a three-column file from files x, y, and z:

paste x y z > file

List users in two columns:

who | paste - -

Merge each pair of lines into one line:

paste -s -d"\t\n" list

patch

patch [options] [original [patchfile]]

Apply the patches specified in patchfile to original. Replace the original with the new, patched version; move the original to original.orig or original~. The patch file is a difference listing produced by the diff command.

Options

-b, --backup

Back up the original file.

--backup-if-mismatch, --no-backup-if-mismatch

When not backing up all original files, these options control whether a backup should be made when a patch does not match the original file. The default is to make backups unless --posix is specified.

-c, --context

Interpret patchfile as a context diff.

-d dir, --directory=dir

cd to directory before beginning patch operations.

--dry-run

Print results of applying a patch, but don't change any files.

-e, --ed

Treat the contents of patchfile as ed commands.

-f, --force

Force all changes, even those that look incorrect. Skip patches if the original file does not exist; force patches for files with the wrong version specified; assume patches are never reversed.

-g num, --get num

Specify whether to check the original file out of source control if it is missing or read-only. If num is a positive number, get the file. If it is negative, prompt the user. If it is 0, do not check files out of source control. The default is negative or the value of the PATCH_GET environment variable when set, unless the --posix option is given. Then the default is 0.

--help

Read patch from file instead of stdin.

-i file, --input=file

-l, --ignore-whitespace

Ignore whitespace while pattern matching.

-n, --normal

Interpret patch file as a normal diff.

-o file, --output=file

Print output to file.

-p[num], --strip[=num]

Specify how much of preceding pathname to strip. A num of 0 strips everything, leaving just the filename. 1 strips the leading /. Each higher number after that strips another directory from the left.

--quoting-style=style

Set the quoting style used when printing names. The default style is shell unless set by the environment variable QUOTING_STYLE. style may be one of the following:

c: Quote as a C language string.
escape: Like c, but without surrounding double-quote characters.
literal: Print without quoting.
shell: Quote for use in shell when needed.
shell-always: Quote for use in shell even if not needed.

--posix

Conform more strictly to the POSIX standard.

-r file, --reject-file=file

Place rejects (hunks of the patch file that patch fails to place within the original file) in file. Default is original.rej.

-s, --silent, --quiet

Suppress commentary.

-t, --batch

Skip patches if the original file does not exist.

-u, --unified

Interpret patch file as a unified context diff.

--verbose

Print version number and exit.

-v, --version

-z suffix, --suffix=suffix

Back up the original file in original.suffix.

-B prefix, --prefix=prefix

Prepend prefix to the backup filename.

-D string, --ifdef=string

Mark all changes with:

#ifdef
   string
#endif

-E, --remove-empty-files

If patch creates any empty files, delete them.

-F num, --fuzz=num

Specify the maximum number of lines that may be ignored (fuzzed over) when deciding where to install a hunk of code. The default is 2. Meaningful only with context diffs.

-N, --forward

Ignore patches that appear to be reversed or to have already been applied.

-R, --reverse

Do a reverse patch: attempt to undo the damage done by patching with the old and new files reversed.

-T, --set-time

When original file timestamps match the times given in the patch header, set timestamps for patched files according to the context diff headers. Use option -f to force date changes. Assume timestamps are in local time.

-V method, --version-control=method

Specify method for creating backup files (overridden by -B):

t, numbered: Make numbered backups.
nil, existing: Back up files according to preexisting backup schemes, with simple backups as the default. This is patch's default behavior.
never, simple: Make simple backups.

-Y prefix, --basename-prefix=prefix

Use the specified prefix with a file's basename to create backup filenames. Useful for specifying a directory.

-Z, --set-utc

Environment variables

TMPDIR, TMP, TEMP: Specify the directory for temporary files; /tmp by default.
SIMPLE_BACKUP_SUFFIX: Suffix to append to backup files instead of .orig or ~.
QUOTING_STYLE: Specify how output should be quoted (see --quoting-style).
PATCH_GET: Specify whether patch should retrieve missing or read-only files from source control (see -g).
POSIXLY_CORRECT: When set, patch conforms more strictly to the POSIX standard (see --posix).
VERSION_CONTROL, PATCH_VERSION_CONTROL: Specify what method to use in naming backups (see -V).

pathchk

pathchk [option] filenames

Determine validity and portability of filenames. Specifically, determine if all directories within the path are searchable and if the length of the filenames is acceptable.

Options

-p, --portability: Check portability for all POSIX systems.
--help: Print a help message and then exit.
--version: Print version information and then exit.

perl

perl

A powerful text-processing language that combines many of the most useful features of shell programs, C, awk, and sed, as well as adding extended features of its own. For more information, see Learning Perl and Programming Perl (both from O'Reilly).

pidof

pidof [options] programs

Display the process IDs of the listed program or programs. pidof is actually a symbolic link to killall5.

Options

-o pids: Omit all processes with the specified process IDs.
-s: Return a single process ID.
-x: Also return process IDs of shells running the named scripts.

ping

ping [options] host

System administration command. Confirm that a remote host is online and responding. ping is intended for use in network testing, measurement, and management. Because of the load it can impose on the network, it is unwise to use ping during normal operations or from automated scripts.

Options

-a

Make ping audible. Beep each time response is received.

-b

Ping a broadcast address.

-c count

Stop after sending (and receiving) count ECHO_RESPONSE packets.

-d

Set SO_DEBUG option on socket being used.

-f

Flood ping-output packets as fast as they come back or 100 times per second, whichever is more. This can be very hard on a network and should be used with caution. Only a privileged user may use this option.

-i wait

Wait wait seconds between sending each packet. Default is to wait 1 second between each packet. This option is incompatible with the -f option.

-l preload

Send preload number of packets as fast as possible before falling into normal mode of behavior.

-n

Numeric output only. No attempt will be made to look up symbolic names for host addresses.

-p digits

Specify up to 16 pad bytes to fill out packet sent. This is useful for diagnosing data-dependent problems in a network. digits are in hex. For example, -p ff will cause the sent packet to be filled with all 1s.

-q

Quiet output--nothing is displayed except the summary lines at startup time and when finished.

-r

Bypass the normal routing tables and send directly to a host on an attached network.

-s packetsize

Specify number of data bytes to be sent. Default is 56, which translates into 64 ICMP data bytes when combined with the 8 bytes of ICMP header data.

-t n

Set the IP Time to Live to n seconds.

-v

Verbose; list ICMP packets received other than ECHO_RESPONSE.

-w n

Exit ping after n seconds.

-A

Adapt to return interval of packets. Like -f ping, sends packets at approximately the rate at which they are received. This option may be used by an unprivileged user.

-I name

Set source address to interface name. name may also be specified as an IP address.

-L

If destination is a multicast address, suppress loopback.

-Q tos

Set Quality of Service on ICMP datagrams.

-S size

Set send buffer (SNDBUF) size. The default is the size of one packet.

-T option

Set IP timestamp options. Accepted option values are:

tsonly: Timestamps only.
tsandaddr: Timestamps and addresses.
tsprespec hosts: Timestamps with prespecified hops of one or more hosts.

-M hint

Specify Path MTU Discovery strategy. Accepted values are do, want, or dont.

-R

Set the IP record route option, which will store the route of the packet inside the IP header. The contents of the record route will be printed if the -v option is given, and will be set on return packets if the target host preserves the record route option across echoes or the -l option is given.

-U

Use older ping behavior and print full user-to-user latency instead of network round trip time.

-V

Print version, then exit.

portmap

rpc.portmap [options]

NFS/NIS command. RPC program number to IP port mapper. portmap is a server that converts RPC program numbers to IP port numbers. It must be running in order to make RPC calls. When an RPC server is started, it tells portmap what port number it is listening to and what RPC program numbers it is prepared to serve. When a client wishes to make an RPC call to a given program number, it first contacts portmap on the server machine to determine the port number where RPC packets should be sent. portmap must be the first RPC server started.

Options

-d: Run portmap in debugging mode. Does not allow portmap to run as a daemon.
-v: Run portmap in verbose mode.

poweroff

poweroff [options]

System administration command. Close out filesystems, shut down the system, and power off. Because this command immediately stops all processes, it should be run only in single-user mode. If the system is not in runlevel 0 or 6, poweroff calls shutdown -h, then performs a poweroff.

Options

-d: Suppress writing to /var/log/wtmp.
-f: Call reboot or halt and not shutdown, even when shutdown would normally be called. This option is used to force a hard halt or reboot.
-h: Place hard drives in standby mode before halt or poweroff.
-i: Shut down network interfaces before reboot.
-n: Suppress normal call to sync.
-w: Suppress normal execution; simply write to /var/log/wtmp.

pppd

pppd [tty] [speed] [options]

System administration command. PPP stands for the Point-to-Point Protocol; it allows datagram transmission over a serial connection. pppd attempts to configure tty for PPP (searching in /dev) or, by default, the controlling terminal. You can also specify a baud rate of speed. pppd accepts many options. Only the most common options are listed here.

Options

asyncmap map: Specify which control characters cannot pass over the line. map should be a 32-bit hex number, where each bit represents a character to escape. For example, bit 00000001 represents the character 0x00; bit 80000000 represents the character 0x1f or _. You may specify multiple characters.
auth: Require self-authentication by peers before allowing packets to move.
call file: Read options from file in /etc/ppp/peers/. Unlike the file option, call file may contain privileged options, even when pppd is not run by root.
connect command: Connect as specified by command, which may be a binary or shell command.
crtscts: Use hardware flow control.
debug: Log contents of control packets to syslogd.
defaultroute: Add a new default route in which the peer is the gateway. When the connection shuts down, remove the route.
nodetach: Operate in the foreground. By default, pppd forks and operates in the background.
disconnect command: Close the connection as specified by command, which may be a binary or shell command.
domain d: Specify a domain name of d.
escape character-list: Escape all characters in character-list, which should be a comma-separated list of hex numbers. You cannot escape 0x20-0x3f or 0x5e.
file file: Consult file for options.
init script: Run specified command or shell script to initialize the serial line.
lock: Allow only pppd to access the device.
mru bytes: Refuse packets of more than bytes bytes.
mtu bytes: Do not send packets of more than bytes bytes.
name name: Specify a machine name for the local system.
netmask mask: Specify netmask (for example, 255.255.255.0).
passive, -p: Do not exit if peer does not respond to attempts to initiate a connection. Instead, wait for a valid packet from the peer.
silent: Send no packets until after receiving one.
[local_IP_address]:[remote_IP_address]: Specify the local and/or remote interface IP addresses, as hostnames or numeric addresses.

Files

/var/run/pppn.pid: pppd's process ID. The n in pppn.pid is the number of the PPP interface unit corresponding to this pppd process.
/etc/ppp/ip-up: Binary or script to be executed when the PPP link becomes active.
/etc/ppp/ip-down: Binary or script to be executed when the PPP link goes down.
/etc/ppp/pap-secrets: Contains usernames, passwords, and IP addresses for use in PAP authentication.
/etc/ppp/options: System defaults. Options in this file are set before the command-line options.
~/.ppprc: The user's default options. These are read before command-line options but after the system defaults.
/etc/ppp/options.ttyname: Name of the default serial port.

pr [options] [files]

Convert a text file or files to a paginated, columned version, with headers. If - is provided as the filename, read from standard input.

Options

+beg_pag[:end-pag], --pages=[beg_pag[:end-pag]: Begin printing on page beg_pag and end on end-pag if specified.
-num_cols, --columns=num_cols: Print in num_cols number of columns, balancing the number of lines in the columns on each page.
-a, --across: Print columns horizontally, not vertically.
-c, --show-control-chars: Convert control characters to hat notation (such as ^C), and other unprintable characters to octal backslash format.
-d, --double-space: Double space.
-D format, --date-format=format: Format the header date using format. See the date command for the possible formats.
-e[tab-char[width]], --expand-tabs=[tab-char[width]]: Convert tabs (or tab-chars) to spaces. If width is specified, convert tabs to width characters (default is 8).
-f, -F, --form-feed: Separate pages with form feeds, not newlines.
-h header, --header=header: Use header for the header instead of the filename.
-i[out-tab-char[out-tab-width]], --output-tabs[=out-tab-char[out-tab-width]]: Replace spaces with tabs on output. Can specify alternative tab character (default is tab) and width (default is 8).
-J, --join-lines: Merge full lines; ignore -W if set.
-l lines, --length=lines: Set page length to lines (default is 66). If lines is less than 10, omit headers and footers.
-m, --merge: Print all files, one per column.
-n[delimiter[digits]], --number-lines[=delimiter[digits]]: Number columns, or, with the -m option, number lines. Append delimiter to each number (default is a tab) and limit the size of numbers to digits (default is 5).
-N num, --first-line-number=num: Start counting with num at the first line of the first page printed. Also see +beg_page.
-o width, --indent=width: Set left margin to width. Does not affect the page width set with -w or -W.
-r, --no-file-warnings: Continue silently when unable to open an input file.
-s[delimiter], --separator[=delimiter]: Separate columns with delimiter (default is a tab) instead of spaces.
-S[string], --sep-string[=string]: Separate columns with string. Default is a tab with -J and a space otherwise.
-t, --omit-header: Suppress headers, footers, and fills at end of pages.
-T, --omit-pagination: Like -t but also suppress form feeds.
-v, --show-non-printing: Convert unprintable characters to octal backslash format.
-w page_width, --width=page_width: Set the page width to page_width characters for multi-column output. Default is 72.
-W page_width, --page-width=page_width: Set the page width to always be page_width characters. Default is 72.
--help: Print a help message and then exit.
--version: Print version information and then exit.

praliases

praliases [options]

System administration command. praliases prints the current sendmail mail aliases. (Usually defined in the /etc/aliases or /etc/aliases.db file.)

Options

-f file: Read the aliases from the specified file instead of sendmail's default alias files.
-C file: Read sendmail configuration from the specified file instead of from /etc/mail/sendmail.cf.

printenv

printenv [option] [variables]printenv option

Print values of all environment variables or, optionally, only the specified variables.

Options

--help: Print usage information and exit.
--version: Print version information and exit.

printf

printf formats [strings]printf option

Print strings using the specified formats. formats can be ordinary text characters, C-language escape characters, C format specifications ending with one of the letters diouxXfeEgGcs or, more commonly, a set of conversion arguments listed here.

Options

--help: Print usage information and exit.
--version: Print version information and exit.

Arguments

%%: Print a single %.
%b: Print string with \ escapes interpreted.
%s: Print the next string.
%n$s: Print the nth string.
%[-]m[.n]s: Print the next string, using a field that is m characters wide. Optionally, limit the field to print only the first n characters of string. Strings are right-adjusted unless the left-adjustment flag, -, is specified.

Examples

printf '%s %s\n' "My files are in" $HOME
printf '%-25.15s %s\n' "My files are in" $HOME

ps [options]

Report on active processes. ps has three types of options. GNU long options start with two dashes, which are required. BSD options may be grouped and do not start with a dash, while Unix98 options may be grouped and require an initial dash. The meaning of the short options can vary depending on whether or not there is a dash. In options, list arguments should either be separated by commas or put in double quotes. In comparing the amount of output produced, note that e prints more than a and l prints more than f for each entry.

Options

nums, p nums, -p nums, --pid=nums: Include only specified processes, which are given in a space-delimited list.
-nums, --sid=nums: Include only specified session IDs, which are given in a space-delimited list.
[-]a: As a, list all processes on a terminal. As -a, list all processes on a terminal except session leaders.
[-]c: As -c, show different scheduler information with -l. As c, show the true command name.
-C cmds: Select by command name.
--cols=cols, --columns=cols, --width=cols: Set the output width (the number of columns to display).
-d: Select all processes except session leaders.
-e, -A: Select all processes.
e: Include environment information after the command.
[-]f, --forest: As -f, display full listing. As f or --forest, display "forest" family tree format, with ASCII art showing the relationships.
-g list, -G list, --group=groups, --Group=groups: For -g, select by session leader if list contains numbers, or by group if it contains group names. For -G, select by the group IDs in list. --group selects by effective group and --Group selects by real group, where groups can be either group names or group IDs.
h, --no-headers: Suppress header. If you select a BSD personality by setting the environment variable PS_PERSONALITY to bsd, then h prints a header on each page.
-H: Display "forest" family tree format, without ASCII art.
--headers: Repeat headers.
--help: Display help information and exit.
--info: Print debugging information.
[-]j: Jobs format. j prints more information than -j.
[-]l: Produce a long listing. -l prints more information than l.
L: Print list of field specifiers that can be used for output formatting or for sorting.
--lines=num, --rows=num: Set the screen height to num lines. If --headers is also set, the headers repeat every num lines.
[-]m: Show threads.
n: Print user IDs and WCHAN numerically.
-nfile, Nfile: Specify the System.map file for ps to use as a namelist file. The map file must correspond to the Linux kernel; e.g., /boot/System.map-2.4.19.
-N, --deselect: Negate the selection.
[-]o fields, --format=fields: As -o, o, or --format, specify user-defined format with a list of fields to display.
[-]O fields: As -O, is like -o, but some common fields are predefined. As O, can be either the same as -O in specifying fields to display, or can specify single-letter fields for sorting. For sorting, each field specified as a key can optionally have a leading + (return to default sort direction on key) or - (reverse the default direction).
r: Show only processes that are currently running.
s: Display signal format.
-s sessions: Show processes belonging to the specified sessions.
-S, --cumulative: Include some dead child process data in parent total.
[-]tttys, --tty=ttys: Display processes running on the specified terminals.
T: Display all processes on this terminal.
[-]u [users], --user=users: As u with no argument, display user-oriented output . As -u or --users, display by effective user ID (and also support names), showing results for users. With no argument, -u displays results for the current user.
[-]U users, --User=users: As U, display processes for the specified users. As -U or --User, display processes for users by real user ID (and also support names).
v: Display virtual memory format.
[-]V, --version: Display version information and then exit.
[-]w: Wide format. Don't truncate long lines.
x: Display processes without an associated terminal.
X: Use old Linux i386 register format.
-y: Do not show flags; show rss instead of addr.

Sort keys

c, cmd: Name of executable.
C, cmdline: Whole command line.
f, flags: Flags.
g, pgrp: Group ID of process.
G, tpgid: Group ID of associated tty.
j, cutime: Cumulative user time.
J, cstime: Cumulative system time.
k, utime: User time.
K, stime: System time.
m, min_flt: Number of minor page faults.
M, maj_flt: Number of major page faults.
n, cmin_flt: Total minor page faults.
N, cmaj_flt: Total major page faults.
o, session: Session ID.
p, pid: Process ID.
P, ppid: Parent's process ID.
r, rss: Resident set size.
R, resident: Resident pages.
s, size: Kilobytes of memory used.
S, share: Number of shared pages.
t, tty: Terminal.
T, start_time: Process's start time.
U, uid: User ID.
u, user: User's name.
v, vsize: Bytes of virtual memory used.
y, priority: Kernel's scheduling priority.

Fields

%CPU

Percent of CPU time used recently.

%MEM

Percent of memory used.

ADDR

Address of the process.

C, CMD, COMMAND

The command the process is running.

ELAPSED

Elapsed time since the start of the process.

F

Process flags:

001: Print alignment warning messages.
002: Being created.
004: Being shut down.
010: ptrace(0) has been called.
020: Tracing system calls.
040: Forked but didn't exec.
100: Used superuser privileges.
200: Dumped core.
400: Killed by a signal.

GROUP

Effective group ID.

NI

The nice value of the process. A higher number indicates less CPU time.

PAGEIN

Number of major page faults.

PID

Process ID.

PPID

Parent process ID.

PRI

Process's scheduling priority. A higher number indicates lower priority.

RSS

Resident set size (the amount of physical memory), in kilobytes.

SHARE

Shared memory.

SIZE

Size of virtual image.

STAT

Status:

R: Runnable.
T: Stopped.
D: Asleep and not interruptible.
S: Asleep.
Z: Zombie.
W: No resident pages (second field).
N: Positive nice value (third field).

STIME

Process start time.

SWAP

Amount of swap used, in kilobytes.

TIME

Cumulative CPU time.

TRS

Size of resident text.

TT, TTY

Associated terminal.

UID

User ID.

VSZ

Virtual memory size, in kilobytes.

WCHAN

Kernel function in which process resides.

pwck

pwck [option] [files]

System administration command. Remove corrupt or duplicate entries in the /etc/passwd and /etc/shadow files. pwck will prompt for a "yes" or "no" before deleting entries. If the user replies "no," the program will exit. Alternate passwd and shadow files can be checked. If correctable errors are found, the user will be encouraged to run the usermod command.

Option

-r: Run in noninteractive read-only mode, answering all questions no.

Exit status

0: Success.
1: Syntax error.
2: One or more bad password entries found.
3: Could not open password files.
4: Could not lock password files.
5: Could not write password files.

pwconv

pwconvpwunconv

System administration command. Convert unshadowed entries in /etc/passwd into shadowed entries in /etc/shadow. Replace the encrypted password in /etc/password with an x. Shadowing passwords keeps them safe from password-cracking programs. pwconv creates additional expiration information for the /etc/shadow file from entries in your /etc/login.defs file. If you add new entries to the /etc/passwd file, you can run pwconv again to transfer the new information to /etc/shadow. Already shadowed entries are ignored. pwunconv restores the encrypted passwords to your /etc/passwd file and removes the /etc/shadow file. Some expiration information is lost in the conversion. See also grpconv and grpunconv.

pwd

pwd

Print the full pathname of the current working directory. See also the dirs shell command, built in to both bash and tcsh.

python

python

A powerful object-oriented scripting language often compared to Perl or Java. python drives many of the configuration scripts used in Red Hat and other Linux distributions. For more information, see Learning Python and Programming Python (both from O'Reilly).

quota

quota [options] [user|group]

Display disk usage and total space allowed for a designated user or group. With no argument, the quota for the current user is displayed. This command reports quotas for all filesystems listed in /etc/mtab. Most users can display only their own quota information, but the superuser can display information for any user.

Options

-F format: Show quota for the specified format. If not specified, autodetects the format.
-g: Given with a user argument, display the quotas for the groups of which the user is a member instead of the user's quotas. With no argument, shows group quotas for the current user.
-q: Display information only for filesystems in which the user is over quota.
-s: Try to choose units for displaying limits, space used, and inodes used.
-u: The default behavior. When used with -g, display both user and group quota information.
-v: Display quotas for filesystems even if no storage is currently allocated.

Formats

rpc: Quota over NFS.
vfsold: Version 1 quota.
vfsv0: Version 2 quota.
xfs: Quota on XFS filesystem.

raidstart

raidstart [options] [devices]
raidstop [options] [devices]

System administration command. Start or stop RAID devices as defined in the RAID configuration file, /etc/raidtab. If option -a (or --all) is used, no devices need to be given; the command will be applied to all the devices defined in the configuration file.

Options

-a, --all: Apply command to all devices defined in the RAID configuration file.
-c file, --configfile file: Use file instead of /etc/raidtab.
-h, --help: Print usage message and exit.
-V, --version: Print version and exit.

ramsize

ramsize [option] [image [size [offset]]]

System administration command. If no options are specified, print usage information for the RAM disk. The pair of bytes at offset 504 in the kernel image normally specify the RAM size; with a kernel image argument, print the information found at that offset. To change that information, specify a new size (in kilobytes). You may also specify a different offset. rdev -r is the same as ramsize.

Option

-o offset: Same as specifying an offset as an argument.

ranlib

ranlib filename
ranlib option

Generate an index for archive file filename. Same as running ar -s.

Option

-v, -V, --version: Print version information and exit.

rarpd

rarpd [options] [interface]

System administration command. Respond to Reverse Address Resolution Protocol (RARP) requests. Some machines (primarily diskless SUN machines) will use RARP requests at boot time to discover their IP address and retrieve boot images. The request contains the booting machine's ethernet address, and rarpd tells it which IP to use. To answer requests, rarpd checks the ethers database (either the /etc/ethers file or read from NIS+) and performs DNS lookups as needed. rarpd will respond to RARP requests only from machines for which it has a bootable image, usually stored in the TFTP boot directory /tftpboot. The daemon will bind to the given interface if specified. This daemon replaces the kernel-based RARP support found in kernels previous to 2.2.

Options

-a: Do not bind to the specified interface.
-b directory: Look for boot images in the specified directory instead of the default /tftpboot.
-d: Do not detach and run in daemon mode. Used for debugging.
-e: Answer requests without checking the TFTP boot directory.
-v: Verbose mode.
-A

raw

raw [options] [rawnode [blockdevice]]

System administration command. Bind a raw character device to a block device, or query current raw device bindings. The rawnode should be a device in /dev/raw. The blockdevice may be specified by filename or by its major and minor device numbers.

Options

-a: Print information on all raw device bindings. Used with option -q.
-h: Print usage information, then exit.
-q: Print information on binding of the specified rawnode, or all raw nodes if accompanied with the -a option.

rcp

rcp [options] file1 file2
rcp [options] file ... directory

Copy files between two machines. Each file or directory is either a remote filename of the form rname@rhost:path, or a local filename.

Options

-k: Attempt to get tickets for remote host; query krb_realmofhost to determine realm.
-p: Preserve modification times and modes of the source files.
-r: If any of the source files are directories, descend into each directory and recursively copy all files and directories within it. The destination must be a directory.
-x: Turns on DES encryption for all data passed by rcp.

rcs

rcs [options] files

The Revision Control System (RCS) keeps track of multiple versions of files, letting you store and retrieve revisions and track the history of the files. The rcs command creates new RCS files and modifies attributes of existing files. See Chapter 14 for more information on RCS and its commands. See Chapter 15 for the newer and more powerful CVS system.

rdate

rdate [options] [host...]

TCP/IP command. Retrieve the date and time from a host or hosts on the network and optionally set the local system time.

Options

-p: Print the retrieved dates.
-s: Set the local system time from the host; must be specified by root.

rdev

rdev [options] [image [value [offset]]]

System administration command. If invoked with no arguments, show the current root filesystem in /etc/mtab syntax. Otherwise, change the values in the kernel image that specify the RAM disk size (by default located at decimal byte offset 504 in the kernel), VGA mode (default 506), and root device (default 508). You must specify the kernel image to be changed, and may specify a new value and a different offset. Using rdev to change these values directly in an image file is discouraged. These values can all be set by a boot loader such as lilo or grub.

Options

-o offset: Same as specifying an offset as an argument. The offset is given in decimal.
-r: Behave like ramsize.
-v: Behave like vidmode.
-R: Behave like rootflags.

rdist

rdist [options] [names]

System administration command. Remote file distribution client program. rdist maintains identical copies of files over multiple hosts. It reads commands from a file named distfile to direct the updating of files and/or directories. An alternative distfile can be specified with the -f option or the -c option.

Options

-a num

Do not update filesystems with fewer than num bytes free.

-c name [login@]host[:dest]

Interpret the arguments as a small distfile, where login is the user to log in as, host is the destination host, name is the local file to transfer, and dest is the remote name where the file should be installed.

-d var=value

Define var to have value. This option defines or overrides variable definitions in the distfile. Set the variable var to value.

-f file

Read input from file (by default, distfile). If file is -, read from standard input.

-l options

Specify logging options on the local machine.

-m machine

Update only machine. May be specified multiple times for multiple machines.

-n

Suppress normal execution. Instead, print the commands that would have been executed.

-ooptions

Specify one or more options, which must be comma-separated.

chknfs: Suppress operations on files that reside on NFS filesystems.
chkreadonly: Check filesystem to be sure it is not read-only before attempting to perform updates.
chksym: Do not update files that exist on the local host but are symbolic links on the remote host.
compare: Compare files; use this comparison rather than age as the criteria for determining which files should be updated.
follow: Interpret symbolic links, copying the file to which the link points instead of creating a link on the remote machine.
ignlnks: Ignore links that appear to be unresolvable.
nochkgroup: Do not update a file's group ownership unless the entire file needs updating.
nochkmode: Do not update file mode unless the entire file needs updating.
nochkowner: Do not update file ownership unless the entire file needs updating.
nodescend: Suppress recursive descent into directories.
noexec: Suppress rdist of executables that are in a.out format.
numchkgroup: Check group ownership by group ID instead of by name.
numchkowner: Check file ownership by user ID instead of by name.
quiet: Quiet mode; do not print commands as they execute.
remove: Remove files that exist on the remote host but not the local host.
savetargets: Save updated files in name.old.
sparse: Check for sparse files, for example ndbm files.
verify: Print a list of all files on the remote machine that are out of date, but do not update them.
whole: Preserve directory structure by creating subdirectories on the remote machine. For example, if you rdist the file /foo/bar into the directory /baz, it would produce the file /baz/foo/bar instead of the default /baz/bar.
younger: Do not update files that are younger than the master files.

-p path

Specify the path to search for rdistd on the remote machine.

-t seconds

Specify the timeout period (default 900 seconds) after which rdist will sever the connection if the remote server has not yet responded.

-A num

Specify the minimum number of inodes that rdist requires.

-D

Debugging mode.

-F

Execute all commands sequentially, without forking.

-L options

Specify logging options on the remote machine.

-M num

Do not allow more than num child rdist processes to run simultaneously. Default is 4.

-P path

Specify path to the transport command to use on the local machine. This is normally rsh, but may also be ssh. The path argument may also be specified as a colon-separated list of acceptable transports to use in order of preference.

-V

Display version, then exit.

rdistd

rdistd options

System administration command. Start the rdist server. Note that you must specify the -S option unless you are simply querying for version information with -V.

Options

-D: Debugging mode.
-S: Start the server.
-V: Display the version number and exit.

readelf

readelf option[...] elffiles

Display information about about one or more ELF (Executable and Linking Format) object files. At least one option is required to specify the information to be displayed for each file. readelf does not currently work on archive files or 64-bit ELF files.

Options

-a, --all: Display all. Equivalent to -h -l -S -s -r -d -n -V.
-d, --dynamic: Display the dynamic section.
-D, --use-dynamic: When displaying symbols, use the symbol table in the dynamic section, not the symbols section.
-e, --headers: Display all headers. Equivalent to -h -l -s.
-h, --file-header: Display the ELF header at the beginning of the file.
--help: Display help information and exit.
--histogram: Display a histogram of bucket bit lengths when displaying the symbol tables.
-l, --program-headers, --segments: Display the segment headers, if any.
-n, --notes: Display the NOTE segment, if any.
-r, --relocs: Display the relocation segment, if any.
-s, --symbols, --syms: Display entries in symbol table sections, if any.
-S, --section-headers, --sections: Display the section headers, if any.
-u, --unwind: Display the unwind section, if any (currently applies only to IA64 ELF files).
-v, --version: Display version information and exit.
-V, --version-info: Display the version sections, if any.
-w[option], --debug-dump[=option]: Display the debug sections. If specified with an option, display only that section. The options shown here in parentheses are for -w; the words preceding them are for --debug-dump. The options are line (l), info (i), abbrev (a), pub-names (p), ranges (r), macro (m), frames (f), frames-interp (F), str (s), and loc (o).
-W, --wide: Don't break output lines at 80 columns. The default is to break them.
-x num, --hex-dump=num: Display a hexadecimal dump of the section number.

readlink

readlink file
readlink option

Print the contents of the symbolic link file, that is, the name of the file to which the link points.

Options

--help: Print usage information and exit.
--version: Print version information and exit.

reboot

reboot [options]

System administration command. Close out filesystems, shut down the system, then reboot. Because this command immediately stops all processes, it should be run only in single-user mode. If the system is not in runlevel 0 or 6, reboot calls shutdown -r.

Options

-d: Suppress writing to /var/log/wtmp.
-f: Call reboot even when shutdown would normally be called.
-i: Shut down network interfaces before reboot.
-n: Suppress normal call to sync.
-w: Suppress normal execution; simply write to /var/log/wtmp.

rename

rename from to files

Rename files by replacing the first occurrence of from in each filename with to.

Example

Rename files that start with test so they start with mytest:

% rename test mytest test*

renice

renice [priority] [options] [target]

Control the scheduling priority of various processes as they run. May be applied to a process, process group, or user (target). A privileged user may alter the priority of other users' processes. priority must, for ordinary users, lie between 0 and the environment variable PRIO_MAX (normally 20), with a higher number indicating increased niceness. A privileged user may set a negative priority, as low as PRIO_MIN (normally -20), to speed up processes.

Options

+num: Specify number by which to increase current priority of process, rather than an absolute priority number.
-num: Specify number by which to decrease current priority of process, rather than an absolute priority number.
-g: Interpret target parameters as process group IDs.
-p: Interpret target parameters as process IDs (default).
-u: Interpret target parameters as usernames.

reset

reset [options] [terminal]

Clear screen (reset terminal). If terminal is specified on the command line, the value is used as the terminal type. reset is a symbolic link to the tset command. Invoking the command as reset is useful for clearing your terminal when a program dies and leaves the terminal in an abnormal state. You may have to run the command with a linefeed character (usually Ctrl-J) before and after it:

Ctrl-JresetCtrl-J

See the tset command for the available options.

resize2fs

resize2fs [options] device [size]

System administration command. Enlarge or shrink an ext2 filesystem on device so it has size blocks. The filesystem size cannot be larger than the underlying partition. This command changes only the filesystem size, not the underlying partition. To change the partition, use fdisk.

Options

-d flags

Print debugging information on resize activity. The value of the flags parameter determines what activity is reported. Compute its value by summing the numbers of the items you wish to debug:

1: Disk I/O.
2: Block relocations.
8: Inode relocations.
16: Inode table movement.
-f: Force resize, overriding safety checks.

-p

Print progress information for each resize task.

rev

rev [file]

Reverse the order of characters on each line of the specified file and print the results on standard output. If no file is specified, rev reads from standard input.

rexecd

rexecd command-line

TCP/IP command. Server for the rexec routine, providing remote execution facilities with authentication based on usernames and passwords. rexecd is started by inetd and must have an entry in inetd's configuration file, /etc/inetd.conf. When rexecd receives a service request, the following protocol is initiated:

The server reads characters from the socket up to a null byte. The resulting string is interpreted as an ASCII number, base 10.
If the number received in Step 1 is nonzero, it is interpreted as the port number of a secondary stream to be used for stderr. A second connection is then created to the specified port on the client's machine.
A null-terminated username of at most 16 characters is retrieved on the initial socket.
A null-terminated, unencrypted password of at most 16 characters is retrieved on the initial socket.
A null-terminated command to be passed to a shell is retrieved on the initial socket. The length of the command is limited by the upper bound on the size of the system's argument list.
rexecd then validates the user, as is done at login time. If the authentication was successful, rexecd changes to the user's home directory and establishes the user and group protections of the user.
A null byte is returned on the connection associated with stderr, and the command line is passed to the normal login shell of the user. The shell inherits the network connections established by rexecd.

Diagnostics

Username too long: Name is longer than 16 characters.
Password too long: Password is longer than 16 characters.
Command too long: Command passed is too long.
Login incorrect: No password file entry for the username exists.
Password incorrect: Wrong password was supplied.
No remote directory: chdir to home directory failed.
Try again: fork by server failed.
<shellname>:...: fork by server failed. User's login shell could not be started.

richtext

richtext [options] [file]

Display MIME ("richtext") files on an ASCII terminal on standard output, by means such as highlighting bold or italic text and displaying underlined text correctly. Intended primarily for use with metamail. If no file is specified, input is taken from standard input.

Options

-c: Don't do any formatting; simply correct the raw richtext and write the results to standard output.
-f: Use termcap-derived escape codes for bold and italic text, even if richtext was called in a pipe.
-m: In multibyte Japanese and Korean sequences, treat < as a real <, not as the start of a richtext command.
-n: Do not correct the raw richtext input.
-o: Use overstrikes for underlines.
-p: Use a pager to view the output. This option has no effect if standard input or standard output is redirected.
-s charset: Use the specified character set as the default. Valid values for charset are us-ascii (default), iso-2022-jp, and iso-2022-kr.
-t: Use * and _ instead of termcap-derived escape codes to highlight text.

rlogin

rlogin [options] rhost

Remote login. rlogin connects the terminal on the current local host system to the remote host system rhost. The remote terminal type is the same as your local terminal type. The terminal or window size is also copied to the remote system if the server supports it.

Options

-8: Allow an 8-bit input data path at all times.
-ec: Specify escape character c (default is ~).
-d: Debugging mode.
-k: Attempt to get tickets from remote host, requesting them in the realm as determined by krb_realm-ofhost.
-l username: Specify a different username for the remote login. Default is the same as your local username.
-E: Do not interpret any character as an escape character.
-L: Allow rlogin session to be run without any output postprocessing (i.e., run in litout mode).

rlogind

in.rlogind [options]

TCP/IP command. Server for the rlogin program, providing a remote login facility, with authentication based on privileged port numbers from trusted hosts. rlogind is invoked by inetd when a remote login connection is requested, and executes the following protocol:

The server checks the client's source port. If the port is not in the range 512-1023, the server aborts the connection.
The server checks the client's source address and requests the corresponding hostname. If the hostname cannot be determined, the dot-notation representation of the host address is used.

The login process propagates the client terminal's baud rate and terminal type as found in the TERM environment variable.

Options

-a: Verify hostname.
-h: Permit superuser .rhosts files to be used. Ignored if pluggable authentication module (PAM) support is enabled. Control through /etc/pam.conf instead.
-l: Do not authenticate hosts via a nonroot .rhosts file. Ignored if pluggable authentication module (PAM) support is enabled. Control through /etc/pam.conf instead.
-n: Suppress keep-alive messages.
-L: Do not authenticate hosts via .rhosts or hosts.equiv files. Ignored if pluggable authentication module (PAM) support is enabled. Control through /etc/pam.conf instead.

rm [options] files

Delete one or more files. To remove a file, you must have write permission in the directory that contains the file, but you need not have permission on the file itself. If you do not have write permission on the file, you will be prompted (y or n) to override.

Options

-d, --directory: Remove directories, even if they are not empty. Available only to a privileged user.
-f, --force: Remove write-protected files without prompting.
--help: Print a help message and then exit.
-i, --interactive: Prompt for y (remove the file) or n (do not remove the file).
-r, -R, --recursive: If file is a directory, remove the entire directory and all its contents, including subdirectories. Be forewarned: use of this option can be dangerous.
-v, --verbose: Verbose mode (print the name of each file before removing it).
--version: Print version information and then exit.
--: Mark the end of options. Use this when you need to supply a filename beginning with -.

rmail

rmail [options] users

TCP/IP command. Handle remote mail received via uucp. rmail transforms trace information from mail in UUCP format to the equivalent RFC 822 format, then forwards messages to sendmail.

Options

-D domain: Use domain instead of UUCP as the UUCP host name in From fields.
-T: Print debugging information.

rmdir

rmdir [options] directories

Delete the named directories (not the contents). directories are deleted from the parent directory and must be empty (if not, rm -r can be used instead). See also mkdir.

Options

--help: Print a help message and then exit.
--ignore-fail-on-non-empty: Ignore failure to remove directories that are not empty.
-p, --parents: Remove directories and any intervening parent directories that become empty as a result. Useful for removing subdirectory trees.
--verbose: Verbose mode; print message for each directory as it is processed.
--version: Print version information and then exit.

rmmod

rmmod [options] modules

System administration command. Unload a module or list of modules from the kernel. This command is successful only if the specified modules are not in use and no other modules are dependent on them.

Options

-a, --all: Autoclean modules; tag unused modules for future cleanings, and remove any currently tagged modules. Tagged modules remain tagged unless used between cleanings.
-e, --persist: Save persistent data for specified modules, or for all modules supporting persistence if none are specified. Do not unload modules.
-h, --help: Print help message then exit.
-r, --stacks: Recursively remove stacked modules (all modules that use the specified module).
-s, --syslog: Write messages to syslogd instead of to the terminal.
-v, --verbose: Verbose mode.
-V, --version: Print modutils version number and help message, then exit.

rootflags

rootflags [option] image [flags [offset]]

System administration command. Set flags for a kernel image. If no arguments are specified, print flags for the kernel image. flags is a 2-byte integer located at offset 498 in a kernel image. Currently the only effect of flags is to mount the root filesystem in read-only mode if flags is nonzero. You may change flags by specifying the kernel image to change, the new flags, and the byte offset at which to place the new information (the default is 498). Note that rdev -R is a synonym for rootflags. If LILO is used, rootflags is not needed. flags can be set from the LILO prompt during a boot.

Option

-o offset: Same as specifying an offset as an argument.

route

route [options] [command]

TCP/IP command. Add or remove entries in the routing tables maintained by routed. route accepts two commands: add, to add a route, and del, to delete a route. The two commands have the following syntax:

add [-net | -host] address [modifiers]
del [-net | -host] address [modifiers]

address is treated as a plain route unless -net is specified or address is found in /etc/networks. -host can be used to specify that address is a plain route whether or not it is found in /etc/networks. Using route modifiers, you can specify the gateway through which to route packets headed for that address, its netmask, TCP mss, or the device with which to associate the route; you can also mask certain routes. Only a privileged user may modify the routing tables.

If no command is specified, route prints the routing tables.

Options

-n, --numeric: Show numerical addresses; do not look up hostnames. (Useful if DNS is not functioning properly.)
-e, --extend: Use netstat -r format to print routing table. Use twice to print extended information. Same as netstat -ree.
-h, --help: Print help message, then exit.
-v, --verbose: Verbose mode.
-A family, --family: Specify an address family to use with an add or del command. family may be inet, inet6, ax25, netrom, ipx, ddp, or x25.
-C, --cache: Perform command on the routing cache instead of the forwarding information base (FIB) routing table.
-F, --fib: Perform command on the forwarding information base (FIB) routing table. This is the default behavior.
-V, --version: Print version and configuration options, then exit.

Route modifiers

netmask mask: Use netmask mask.
gw gateway: Route packets through gateway.
metric n: Set routing metric to n.
mss bytes: Set maximum segment size for connections over this route.
reject: Cause route lookup for target to fail. Used to mask out networks from a default route.
[dev] interface: Associate route with specified device. When the interface is given as the last argument on a command line, the word dev is optional.

routed

routed [options] [logfile]

TCP/IP command. Network routing daemon. routed is invoked by a privileged user at boot time to manage the Internet routing tables. The routing daemon uses a variant of the Xerox NS Routing Information Protocol in maintaining up-to-date kernel routing-table entries. When routed is started, it uses the SIOCGIFCONF ioctl call to find those directly connected interfaces configured into the system and marked up. routed transmits a REQUEST packet on each interface, then enters a loop, listening for REQUEST and RESPONSE packets from other hosts. When a REQUEST packet is received, routed formulates a reply based on the information maintained in its internal tables. The generated RESPONSE packet contains a list of known routes. Any RESPONSE packets received are used to update the routing tables as appropriate.

When an update is applied, routed records the change in its internal tables, updates the kernel routing table, and generates a RESPONSE packet reflecting these changes to all directly connected hosts and networks.

Options

-d: Debugging mode. Log additional information to the logfile.
-g: Offer a route to the default destination.
-q: Opposite of -s option.
-s: Force routed to supply routing information, whether it is acting as an internetwork router or not.
-t: Stop routed from going into background and releasing itself from the controlling terminal, so that interrupts from the keyboard will kill the process.

rpcgen

rpcgen [options] file

Parse file, which should be written in the RPC language, and produce a program written in C that implements the RPC code. Place header code generated from file.x in file.h, XDR routines in file_xdr.c, server code in file_svc.c, and client code in file_clnt.c. Lines preceded by % are not parsed. By default, rpcgen produces Sun OS 4.1-compatible code.

-a: Produce all files (client and server).
-5: Produce SVR4-compatible code.
-c: Create XDR routines. Cannot be used with other options.
-C: Produce ANSI C code (the default).
-K: Produce K&R C code.
-Dname[=value]: Define the symbol name, and set it equal to value or 1.
-h: Produce a header file. With -T, make the file support RPC dispatch tables. Cannot be used with other options.
-I: Produce an inetd-compatible server.
-K secs: Specify amount of time that the server should wait after replying to a request and before exiting. Default is 120. A secs of -1 prevents the program from ever exiting.
-l: Produce client code. Cannot be used with other options.
-m: Produce server code only, suppressing creation of a "main" routine. Cannot be used with other options.
-N: New style. Allow multiple arguments for procedures. Not necessarily backward compatible.
-o [file]: Print output to file or standard output.
-Sc: Print sample client code to standard output.
-Ss: Create skeleton server code only.
-t: Create RPC dispatch table. Cannot be used with other options.
-T: Include support for RPC dispatch tables.

rpcinfo

rpcinfo [options] [host] [program] [version]

NFS/NIS command. Report RPC information. program can be either a name or a number. If a version is specified, rpcinfo attempts to call that version of the specified program. Otherwise, it attempts to find all the registered version numbers for the specified program by calling Version 0, and then attempts to call each registered version.

Options

-b program version: Make an RPC broadcast to the specified program and version using UDP, and report all hosts that respond.
-d program version: Delete the specified version of program's registration. Can be executed only by the user who added the registration or a privileged user.
-n portnum: Use portnum as the port number for the -t and -u options, instead of the port number given by the portmapper.
-p [host]: Probe the portmapper on host and print a list of all registered RPC programs. If host is not specified, it defaults to the value returned by hostname.
-t host program [version]: Make an RPC call to program on the specified host using TCP, and report whether a response was received.
-u host program [version]: Make an RPC call to program on the specified host using UDP, and report whether a response was received.

Examples

To show all the RPC services registered on the local machine, use:

$ rpcinfo -p

To show all the RPC services registered on the machine named klaxon, use:

$ rpcinfo -p klaxon

To show all machines on the local network that are running the Network Information Service (NIS), use:

$ rpcinfo -b ypserv version | uniq

where version is the current NIS version obtained from the results of the -p switch earlier in this list.

rpm

rpm [options]

The Red Hat Package Manager. A freely available packaging system for software distribution and installation. RPM packages are built, installed, and queried with the rpm and rpmbuild commands. For detailed information on RPM, see Chapter 5.

rsh

rsh [options] host [command]

Execute command on remote host, or, if no command is specified, begin an interactive shell on the remote host using rlogin.

Options

-d: Enable socket debugging.
-l username: Attempt to log in as username. By default, the name of the user executing rsh is used.
-n: Redirect the input to rsh from the special device /dev/null. (This should be done when backgrounding rsh from a shell prompt, to direct the input away from the terminal.)

rshd

rshd [options]

TCP/IP command. Remote shell server for programs such as rcmd and rcp, which need to execute a noninteractive shell on remote machines. rshd is started by inetd and must have an entry in inetd's configuration file, /etc/inetd.conf.

All options are exactly the same as those in rlogind, except for -L, which is unique to rshd.

Option

-L: Log all successful connections and failed attempts via syslogd.

runlevel

runlevel [utmp]

System administration command. Display the previous and current system runlevels as reported in the utmp file. The default utmp file is /var/run/utmp. See init for a summary of runlevels.

run-parts

run-parts [options] [directory]

System administration command. Run, in lexical order, all scripts found in directory. Exclude scripts whose filenames include nonalphanumeric characters (besides underscores and hyphens).

Options

--: Interpret all subsequent arguments as filenames, not options.
--test: Print information listing which scripts would be run, but suppress actual execution of them.
--umask=umask: Specify umask. The default is 022.

rup

rup [options] [hosts]

TCP/IP command. Query statd for system status on RPC hosts: current time, uptime, and load averages (the average number of jobs in the run queue).

Options

-d: Report local time on each host.
-h: Sort information by hostname.
-l: Sort information by load average.
-s: Print times in seconds. Useful for scripts.
-t: Sort information by uptime.

ruptime

ruptime [options]

TCP/IP command. Provide information on how long each machine on the local network has been up and which users are logged into each. If a machine has not reported in for 11 minutes, assume it is down. The listing is sorted by hostname. ruptime depends on rwhod.

Options

-a: Include users who have been idle for more than one hour.
-l: Sort machines by load average.
-r: Reverse the normal sort order.
-t: Sort machines by uptime.
-u: Sort machines by the number of users logged in.

rusers

rusers [options] [host]

TCP/IP command. List the users logged into host, or to all local machines, in who format (hostname, usernames). rusers depends on rwhod.

Options

-a: Include machines with no users logged in.
-l: Include more information: tty, date, time, idle time, remote host.

rusersd

rpc.rusersd

System administration command. Report information on users logged into the system. Answers queries from rusers.

rwall

rwall host [file]

TCP/IP command. Use RPC to print a message to all users logged into host. If file is specified, read the message from it; otherwise, read from standard input.

rwho

rwho [option]

Report who is logged on for all machines on the local network (similar to who). rwho depends on rwhod.

Option

-a: List users even if they've been idle for more than one hour.

rwhod

rwhod [options]

TCP/IP command. System-status server that maintains the database used by the rwho and ruptime programs. Its operation is predicated on the ability to broadcast messages on a network. As a producer of information, rwhod periodically queries the state of the system and constructs status messages, which are broadcast on a network. As a consumer of information, it listens for other rwhod servers' status messages, validates them, then records them in a collection of files located in the directory /var/spool/rwho. Messages received by the rwhod server are discarded unless they originated at an rwhod server's port. Status messages are generated approximately once every three minutes.

Options

-a: Use both broadcast and point-to-point interfaces. This is the default.
-b: Use only broadcast interfaces.
-p: Use only point-to-point interfaces.
-u user: Run daemon as specified user.

scp

scp [options] file1[...] file2

Securely copy files between hosts on a network, using ssh. Part of the OpenSSH suite of network tools. scp requests a password or passphrase if required. The transfer can be between two remote hosts. If more than one file is specified for file1, file2 should be a directory; otherwise, only the last file in the list is copied. file1 and file2 can be specified in any of the following ways:

file
host:file
user@host:file

Options

-4: Use IPv4 addresses.
-6: Use IPv6 addresses.
-B: Run in batch mode. Don't ask for passwords or passphrases.
-c cipher: Specify the cipher to be used for encrypting the data.
-C: Enable ssh compression.
-i file: Specify the file that contains the identity (private key) for RSA authentication.
-o option: Specify an option to pass to ssh.
-p: Preserve modification time, access time, and mode.
-P port: Connect to port on the remote host.
-q: Don't display the progress meter.
-r: Copy directories recursively.
-S program: Specify the program to use for the encrypted connection. The program must understand ssh options.
-v: Verbose mode.

screen

screen [options] [command [args]]

Provide ANSI/VT100 terminal emulation, making it possible to run multiple full-screen pseudo-terminals from one real terminal, and letting you manipulate and save your screen input and output, copy and paste between windows, etc.

Options

-a: Include all capabilities in each window's termcap.
-A: Adapt all windows to the size of the current terminal. Default is to try to use the previous window size.
-c file: Use file as the configuration file instead of the default $HOME/.screenrc.
-d: Detach session running elsewhere. With -r, reattach to this terminal. With -R, reattach to this terminal or create it if it doesn't already exist. With -RR, use the first session when reattaching if more than one session is available.
-D: Detach session running elsewhere, logging out before detaching. With -r, reattach to this terminal. With -R, reattach to this terminal or create it if it doesn't already exist. With -RR, do whatever is necessary to create a new session.
-e xy: Change command characters. Specify x as the command character (default Ctrl-a) and y as the character that generates a literal command character (default a). Specify in caret notation (e.g., ^A for Ctrl-a).
-f, -fn, -fa: Turn flow control on, off, or to automatic switching mode.
-h num: Specify the size of the history scrollback buffer.
-i: Cause the interrupt key (usually Ctrl-c) to interrupt the display immediately when flow control is on. Use of this option is discouraged.
-l, -ln: Turn login mode on or off for /etc/utmp updating.
-ls, -list: Print list of pid.tty.host strings identifying screen sessions.
-L: Tell screen that automargin terminal has a writable last position.
-m: Ignore the $STY environment variable and create a new session. With -d, start session in detached mode; useful for scripts. With -D, start session in detached mode but don't fork a new process; the command exits if the session terminates.
-O: Use optimal output mode for terminal rather than true VT100 emulation.
-p window: Preselect the specified window if it exists.
-q: Suppress error message printing on startup. Exit with nonzero return code if unsuccessful.
-r [pid.tty.host]
-r sessionowner/[pid.tty.host]: Resume detached session. No other options except -d or -D can be specified. With sessionowner, resume another user's detached session; requires setuid root.
-R: Attempt to resume the first session found, or start a new session with the specified options. Set by default if screen is run as a login shell.
-s shell: Set the default shell, overriding the $SHELL environment variable.
-S name: Specify a name for the session being started.
-t name: Set the window's title.
-T term: Set $TERM to term instead of "screen".
-U: Run in UTF-8 mode.
-v: Print version information and exit.
-wipe [match]: Like -ls, but remove destroyed sessions instead of marking them dead. If a match is specified, it should be in the same form as the argument to the -r option.
-x: Attach to a session that is not detached. Requires multi-display mode.
-X: Run specified command in specified session. Requires multi-display mode, and session must not be password-protected.

Key bindings

screen commands consist of a command character (Ctrl-a by default) followed by another character. For many of the commands, you can also specify the character as Ctrl-character; e.g., Ctrl-a Ctrl-d as well as Ctrl-a d. The default key bindings are listed here. You can change the bindings for yourself in the $HOME/.screenrc configuration file, or for all users in /etc/screenrc. The term in parentheses following the description is the equivalent configuration file command for changing the key binding.

Ctrl-a ': Prompt for window name or number to switch to. (select)
Ctrl-a ": List all windows for selection. (windowlist -b)
Ctrl-a num: Switch to window num, where num is a digit in the range 0-9 or - (the blank window). (select num)
Ctrl-a Tab: Switch input focus to next region. (focus)
Ctrl-a Ctrl-a: Toggle to previously displayed window. (other)
Ctrl-a a: Send the command character (Ctrl-a) to the window. (meta)
Ctrl-a A: Prompt user to enter a name for the current window. (title)
Ctrl-a b: Send a break to the window. (break)
Ctrl-a B: Reopen the terminal line and send a break. (pow-break)
Ctrl-a c: Create a new window with a shell and switch to it. (screen)
Ctrl-a C: Clear the screen. (clear)
Ctrl-a d: Detach screen from this terminal. (detach)
Ctrl-a D D: Detach and log out. (pow-detach)
Ctrl-a f: Toggle flow control between on, off, and auto. (flow)
Ctrl-a F: Resize window to current region size. (fit)
Ctrl-a Ctrl-g: Toggle visual bell mode. (vbell)
Ctrl-a h: Write contents of the current window to the file hardcopy.n. (hardcopy)
Ctrl-a H: Begin/end logging of the current window to the file screenlog.n. (log)
Ctrl-a i: Show information about this window. (info)
Ctrl-a k: Kill current window. (kill)
Ctrl-a l: Refresh current window. (redisplay)
Ctrl-a L: Toggle window's login slot. Requires that screen be configured to update the utmp database. (login)
Ctrl-a m: Redisplay last message. (lastmsg)
Ctrl-a M: Toggle monitoring of the current window. (monitor)
Ctrl-a Space
Ctrl-a n: Switch to next window. (next)
Ctrl-a N: Show number and title of current window. (number)
Ctrl-a Backspace
Ctrl-a h
Ctrl-a p: Switch to previous window. (prev)
Ctrl-a q: Send a start signal (associated with Ctrl-q by terminals) to current window. (xon)
Ctrl-a Q: Delete all regions except the current one. (only)
Ctrl-a r: Toggle current window's line-wrap setting. (wrap)
Ctrl-a s: Send a stop signal (associated with Ctrl-s by terminals) to current window. (xoff)
Ctrl-a S: Split current region into two new regions. (split)
Ctrl-a t: Show system information, including time and date. (time)
Ctrl-a v: Display version information. (version)
Ctrl-a Ctrl-v: Enter digraph for entering characters that can't normally be entered. (digraph)
Ctrl-a w: List all windows. (windows)
Ctrl-a W: Toggle 80/132 columns. (width)
Ctrl-a x: Lock terminal. (lockscreen)
Ctrl-a X: Kill the current region. (remove)
Ctrl-a z: Suspend screen. (suspend)
Ctrl-a Z: Reset virtual terminal to its "power-on" values. (reset)
Ctrl-a .: Write out a .termcap file. (dumptermcap)
Ctrl-a ?: Show all key bindings. (help)
Ctrl-a Ctrl-\: Kill all windows and terminate screen. (quit)
Ctrl-a :: Enter command-line mode. (colon)
Ctrl-a [
Ctrl-a Esc: Enter copy/scrollback mode. (copy)
Ctrl-a ]: Write contents of the paste buffer to the standard input queue of the current window. (paste)
Ctrl-a {
Ctrl-a }: Copy and paste a previous line. (history)
Ctrl-a >: Write paste buffer to a file. (writebuf)
Ctrl-a <: Read screen-exchange file into paste buffer. (readbuf)
Ctrl-a =: Remove file used by Ctrl-a < and Ctrl-a >. (removebuf)
Ctrl-a ,: Shows where screen comes from, where it went to, and why you can use it. (license)
Ctrl-a _: Start/stop monitoring the current window for inactivity. (silence)
Ctrl-a *

script

script [option] [file]

Fork the current shell and make a typescript of a terminal session. The typescript is written to file. If no file is given, the typescript is saved in the file typescript. The script ends when the forked shell exits, usually with Ctrl-D or exit.

Options

-a: Append to file or typescript instead of overwriting the previous contents.
-f: Flush output after each write. Useful if another person is monitoring the output file.
-q: Operate in quiet mode.
-t: Write timing data to standard error. Each entry has two fields: the first is the elapsed time since the last output, and the second is the number of characters in the current output.

sdiff

sdiff -o outfile [options] from to

Find differences between the two files from and to and merge interactively, writing the results to outfile.

Options

--: Treat remaining options as filenames, even if they begin with -.
-a, --text: Treat all files as text and compare line-by-line.
-b, --ignore-space-change: Ignore differences in whitespace.
-B, --ignore-blank-lines: Ignore added or missing blank lines.
-d, --minimal: Use a different algorithm to find fewer changes. This option causes sdiff to run more slowly.
-H, --speed-large-files: Heuristically speed comparison of large files with many small scattered changes.
-i, --ignore-case: Ignore case changes.
-I regexp, --ignore-matching-lines=regexp: Ignore any changes that insert or delete lines matching the regular expression regexp.
--ignore-all-space: Ignore whitespace when comparing lines.
-l, --left-column: Print only the left column of common lines.
-o file, --output=file: Write merged output to the specified file.
-s, --suppress-common-lines: Suppress common lines.
-t, --expand-tabs: Convert tabs to spaces in the output to preserve alignment.
-v, --version: Print version information and exit.
-w cols, --width=cols: Set the output to cols columns wide.
-W: Ignore horizontal whitespace when comparing lines.

Interactive commands

ed: Edit, then use both versions, with a header for each.
eb: Edit, then use both versions.
el: Edit, then use the left version.
er: Edit, then use the right version.
e: Edit a new version to replace the others.
l: Use the left version.
r: Use the right version.
s: Silently include common lines.
v: Verbosely include common lines.
q: Quit.

sed

sed [options] [command] [files]

Stream editor. Edit one or more files without user interaction. See Chapter 12 for more information.

sendmail

sendmail [flags] [address...]

System administration command. sendmail is a mail transfer agent (MTA) or, more simply, a mail router. It accepts mail from a user's mail program, interprets the mail address, rewrites the address into the proper form for the delivery program, and routes the mail to the correct delivery program.

Command-line flags

-Ac

Use local submission configuration file /etc/mail/submit.cf, even when no mail is sent from the command line.

-Am

Use configuration file /etc/mail/sendmail.cf, even when mail is sent from the command line.

-Btype

Set message body type. Accepted values are 7BIT and 8BITMIME.

-bx

Set operation mode to x. Operation modes are:

a: Run in ARPAnet mode.
d: Run as a daemon.
D: Run as a daemon, but remain in the foreground.
h: Print persistent host status information.
H: Purge expired entries from persistent host status information.
i: Initialize the alias database.
m: Deliver mail (the default).
p: Print the mail queue.
s: Speak SMTP on input side.
t: Run in test mode.
v: Verify addresses; do not collect or deliver.

-C file

Use configuration file file.

-d level

Set debugging level.

-F name

Set full name of user to name.

-f name

Sender's name is name.

-G

Relay message submission. Used by rmail.

-i

Do not interpret dots on a line by themselves as a message terminator.

-h cnt

Set hop count (number of times message has been processed by sendmail) to cnt.

-L identifier

Use the specified log identifier for messages sent to syslogd.

-N conditions

Specify conditions for delivery status notification (DSN) as a comma-separated list. Accepted values are never, delay, failure, and success.

-n

Do not alias or forward.

-O option=value

Set an option specified by its long name. Options are described in the next section.

-oXvalue

Set an option specified by its short name X. Options are described in the next section.

-pprotocol

Receive messages via the protocol protocol.

-q[time]

Process queued messages immediately, or at intervals indicated by time (for example, -q30m for every half hour).

-qp[time]

Same as -q, but create a persistent process to handle the queue instead of initiating a new process at each time interval.

-qf

Process saved messages in the queue using the foreground process.

-qG group

Process saved messages in the named queue group.

-q[!]I substring

Process jobs for named queues containing substring. Use ! to process mail for all queues not containing substring.

-q[!]R substring

Process jobs with recipients containing substring. Use ! to process mail for recipients not containing substring.

-q[!]S substring

Process jobs from senders containing substring. Use ! to process mail from senders not containing substring.

-R portion

When bouncing messages, return only the specified portion of the bounced message. portion may be hdrs for headers, or full for the full message.

-r name

Obsolete form of -f.

-t

Read header for To:, Cc:, and Bcc: lines, and send to everyone on those lists.

-v

Use envid as the original envelope ID.

-V envid

-X file

Log all traffic to file. Not to be used for normal logging.

Configuration options

Command-line configuration options are the same options normally set with an O in the sendmail configuration file. On the command line they are set using -O and the option's long name. Many of these options have short name variations that are used with the -o option. Here we document items most likely to be useful on the command line, providing both their short and long name forms. Many of the commands call for timeout values. These should be given as a number followed by a letter indicating the interval: s for seconds, m for minutes, h for hours, or d for days. For example, 30s is 30 seconds, 10m is 10 minutes, 3d is 3 days. The default is minutes when no letter is given.

Aliasfile=file, Afile

Use alternate alias file.

AliasWait=min, amin

If the D option is set, wait min minutes for the aliases file to be rebuilt before returning an alias database out-of-date warning.

BlankSub=char, Bchar

Set unquoted space replacement character.

CheckAliases, n

When running newaliases, validate the right side of aliases.

CheckpointInterval=num, Cnum

Checkpoint the queue when mailing to multiple recipients. sendmail will rewrite the list of recipients after each group of num recipients has been processed.

ClassFactor=factor, zfactor

Multiplier for priority increments. This determines how much weight to give to a message's precedence header. sendmail's default is 1800.

ConnectionCacheSize=num, knum

Specify the maximum number of open connections to cache.

ConnectionCacheTimeout=timeout, Ktimeout

Time out connections after timeout.

ConnectionRateThrottle=num

Restrict SMTP connections per second to num.

DefaultUser=uid[:gid], uuid[:gid]

Use user ID and group ID for mailers instead of 1:1. If no group ID is specified, the user's default group is used.

DefaultCharSet=label

Use the specified label for 8-bit data.

DeliveryMode=x, dx

Set the delivery mode to x. Delivery modes are d for deferred delivery, i for interactive (synchronous) delivery, b for background (asynchronous) delivery, and q for queue only (i.e., deliver the next time the queue is run).

DialDelay=seconds

Specify the number of seconds to wait before redialing after a connection fails.

DontPruneRoutes, R

Don't prune route addresses.

EightBitMode=mode, 8mode

Specify how to handle 8-bit input. Accepted values for mode are mimefy (convert to 7-bit), pass (send as is), or strict (bounce the message).

ErrorHeader=text, Etext

Set error message header. text is either text to add to an error message, or the name of a file. A filename must include its full path and begin with a /.

ErrorMode=x, ex

Set error processing to mode x. Valid modes are m to mail back the error message, w to write back the error message, p to print the errors on the terminal (default), q to throw away error messages, and e to do special processing for the BerkNet.

FallbackMXhost=host, Vhost

Set fallback MX host. host should be the fully qualified domain name of the fallback host.

ForkEachJob, Y

Deliver each job that is run from the queue in a separate process. This helps limit the size of running processes on systems with very low amounts of memory.

ForwardPath=path, Jpath

Set an alternative .forward search path.

HelpFile=file, Hfile

Specify SMTP help file to use instead of /etc/mail/helpfile.

HoldExpensive, c

On mailers that are considered "expensive" to connect to, don't initiate immediate connection.

IgnoreDots, i

Do not take dots on a line by themselves as a message terminator.

LogLevel=n, Ln

Specify log level. Default is 9.

MatchGECOS, G

Compare local mail names to the GECOS section in the password file.

MaxDaemonChildren=num

Restrict incoming SMTP daemon to no more than num child processes.

MaxHopCount=num, hnum

Allow a maximum of num hops per message.

MeToo, m

Send to me (the sender) also if I am in an alias expansion.

MinFreeBlocks=minblocks, bminblocks

Require at least minblocks on the filesystem to be free.

MinQueueAge=timeout

Wait the specified time before processing a new job in the queue.

NoRecipientAction=action

Specify what headers, if any, to add to a message without recipient headers. Accepted values are none, add-to, add-apparently-to, add-bcc, and add-to-undisclosed.

OldStyleHeaders, o

If set, this message may have old-style headers. If not set, this message is guaranteed to have new-style headers (i.e., commas instead of spaces between addresses).

PostmasterCopy=user, Puser

Send copies of all failed mail to user (usually postmaster).

PrivacyOptions=optionlist, poptionlist

Adjust the privacy of the SMTP daemon. The optionlist argument should be a comma-separated list of the following values:

public: Make SMTP fully public (the default).
needmailhelo: Require site to send HELO or ELHO before sending mail.
needexpnhelo: Require site to send HELO or ELHO before answering an address expansion request.
needvrfyhelo: Like preceding argument, but for verification requests.
noetrn: Deny requests to reverse the connection using extended TURN.
noexpn: Deny all expansion requests.
noverb: Deny requests for verbose mode.
novrfy: Deny all verification requests.
authwarnings: Insert special headers in mail messages advising recipients that the message may not be authentic.
goaway: Set all of the previous arguments (except public).
nobodyreturn: Don't return message body with a delivery status notification.
noreceipts: Turn off delivery status notification on success.
restrictexpand: Deny untrusted users access to aliases, forwards, or include files. Restrict sendmail -bv and disallow -v.
restrictmailq: Allow only users of the same group as the owner of the queue directory to examine the mail queue.
restrictqrun: Limit queue processing to root and the owner of the queue directory.

QueueDirectory=dir, Qdir

Select the directory in which to queue messages.

QueueFactor=factor, qfactor

Multiplier (factor) for high-load queuing. Default is 600000.

QueueLA=load, xload

Queue messages when load level is higher than load.

QueueTimeout=timeout, Ttimeout

Set the timeout on undelivered messages in the queue to the specified time (overridden by Timeout.queuereturn).

RecipientFactor=factor, yfactor

Penalize large recipient lists by factor.

RefuseLA=load, Xload

Refuse SMTP connections when load is higher than load.

ResolverOptions=arg, I arg

Use DNS lookups and tune them. Queue messages on connection refused. The arg arguments are identical to resolver flags without the RES_ prefix. Each flag can be preceded by a plus or minus sign to enable or disable the corresponding name server option. There must be whitespace between the I and the first flag.

RetryFactor=inc, Zinc

Increment priority of items remaining in queue by inc after each job is processed. sendmail uses 90,000 by default.

SaveFromLine, f

Save Unix-style From lines at the front of messages.

SendMimeErrors, j

Use MIME format for error messages.

SevenBitInput, 7

Format all incoming messages in seven bits.

StatusFile=file, Sfile

Save statistics in the named file.

SuperSafe, s

Always instantiate the queue file, even when it is not strictly necessary.

TempFileMode=mode, Fmode

Set default file permissions for temporary files. If this option is missing, default permissions are 0600.

Timeout.queuereturn=timeout

Return undelivered mail that has been in the queue longer than the specified timeout. The default is 5d (five days).

TimeZoneSpec=timezone, ttimezone

Set name of the time zone.

UseErrorsTo, l

Do not ignore Errors-To header.

UserDatabaseSpec=database, Udatabase

Consult the user database for forwarding information.

Verbose, v

Run in verbose mode.

sendmail support files

/usr/lib/sendmail: Traditional location of sendmail binary.
/usr/bin/newaliases: Link to /usr/lib/sendmail; rebuilds the alias database from information in /etc/aliases.
/usr/bin/mailq: Prints a listing of the mail queue.
/etc/mail/sendmail.cf: Configuration file, in text form.
/etc/mail/submit.cf: Configuration file used for local message submissions.
/etc/mail/helpfile: SMTP help file.
/etc/mail/statistics: Statistics file.
/etc/aliases: Alias file, in text form.
/etc/aliases.db: Alias file in dbm format. Created by newaliases
/var/spool/mqueue

seq

seq [options] [first [increment]] last

Print the numbers from first through last by increment. The default is to print one number per line to standard output. Both first and increment can be omitted and default to 1, but if first is omitted then increment must also be omitted. In other words, if only two numbers are specified, they are taken to be the first and last numbers. The numbers are treated as floating point.

Options

-f format, --format=format: Write the output using the specified printf floating-point format, which can be one of %e, %f, or %g (the default).
--help: Print help message and exit.
-s string, --separator=string: Use string to separate numbers in the output. Default is newline.
-w, --equal-width: Equalize the width of the numbers by padding with leading zeros. (Use -f for other types of padding.)
--version: Print version information and exit.

setfdprm

setfdprm [options] device [name]

Load disk parameters used when autoconfiguring floppy devices.

Options

-c device: Clear parameters of device.
-n device: Disable format-detection messages for device.
-p device [name | parameters]: Permanently reset parameters for device. You can use name to specify a configuration, or you can specify individual parameters. The parameters that can be specified are dev, size, sect, heads, tracks, stretch, gap, rate, spec1, or fmt_gap. Consult /etc/fdprm for the original values.
-y device: Enable format-detection messages for device.

setkeycodes

setkeycodes scancode keycode

System administration command. Assign a keycode event to the specified keyboard scancode. The kernel matches these to its own keycodes. Scancodes in the range of 1-88 are hardwired in the kernel, but the remaining scancodes can be assigned to keycodes in the range of 1-127. Use getkeycodes to see current assignments. Use showkey to discover what scancode a key is sending.

setleds

setleds [options]

Display or change the led flag settings (NumLock, CapsLock, and ScrollLock) for the current virtual terminal. With no options, display the current settings for all three flags. Can be used in a startup script to set the initial state of the leds.

Options

+num, -num: Set or clear NumLock.
+caps, -caps: Set or clear CapsLock
+scroll, -scroll: Set or clear ScrollLock.
-D: Change both the current and the default settings. Useful for always having NumLock set, for example.
-F: Only change the flags (and their settings may be reflected by the keyboard leds). The default behavior.
-L: Change the leds but not the flags, so the leds no longer reflect the virtual terminal (VT) flags. Run setleds -L with no other options to restore the default behavior.
-v: Report the settings before and after the change.

setmetamode

setmetamode [options]

Display or set Meta key handling for the current virtual terminal. With no option, print the current Meta key mode. Otherwise, set the mode and display the setting before and after the change.

Options

esc, prefix, escprefix: Set the Meta key to send an escape sequence.
meta, bit, metabit: Set the Meta key to set the high-order bit of the character.

setsid

setsid command [arguments]

System administration command. Execute the named command and optional command arguments in a new session.

setterm

setterm [options]

Set terminal attributes by writing to standard output a character string to invoke the specified attributes.

Options

For Boolean options, the default value is on. Where 8-color is specified, the possible colors are black, red, green, yellow, blue, magenta, cyan, and white. Where 16-color is specified, the possible colors include the 8-color colors, plus grey, bright red, bright green, bright yellow, bright blue, bright magenta, bright cyan, and bright white.

-appcursorkeys [on|off]

Set cursor key application mode on or off. Virtual consoles only. Can cause problems with vi.

-append [num]

Write a snapshot of virtual console num to the file specified with the -file option, appending the snapshot to any existing contents. With no argument, write a snapshot of the current virtual terminal.

-background 8-color|default

Set background color. Virtual consoles only.

-bfreq [freq]

Set the bell frequency in Hz (default 0).

-blank [min]

Set the delay before the screen blanks to the specified number of minutes. Virtual consoles only.

-blength [millisec]

Set the bell duration in milliseconds (default 0).

-blink [on|off]

Turn blinking mode on or off. If the terminal is not a virtual console, -blink off also turns off bold, half-bright, and reverse modes.

-bold [on|off]

Turn bold on or off. If the terminal is not a virtual console, -bold off also turns off blink, half-bright, and reverse modes.

-clear [all]

Clear the screen.

-clear rest

Clear from the current cursor position to the end of the screen.

-cleartabs [tab1...tabn]

With no arguments, clear all tab stops. Otherwise, clear the specified tab stops. Virtual consoles only.

-cursor [on|off]

Turn the cursor on or off.

-default

Set rendering options to defaults.

-dump [num]

Write a snapshot of virtual console num to the file specified with the -file option, overwriting any existing contents. With no argument, dump the current virtual console. Overrides -append.

-file file

Write output from the -dump or -append option to the specified file. If no filename is specified, write to the file screen.dump in the current directory.

-foreground 8-color|default

Set foreground color. Virtual consoles only.

-half-bright [on|off]

Turn half-bright (dim) mode on or off. If the terminal is not a virtual console, -half-bright off also turns off bold, blink, and reverse modes.

-hbcolor 16-color

Set color for half-bright characters. Virtual consoles only.

-initialize

Display the terminal initialization string to reset the rendering options and other attributes to their defaults.

-inversescreen [on|off]

Invert the screen colors, swapping foreground and background, and underline and half-bright. Virtual consoles only.

-linewrap [on|off]

Turn line-wrapping on or off. Virtual consoles only.

-msg [on|off]

Enable or disable the sending of kernel printk( ) messages to the console. Virtual consoles only.

-msglevel [num]

Set the console logging level for kernel printk( ) messages. The value of num can be in the range 0-8. Messages more important than the specified number are printed, with 8 printing all kernel messages, and 0 equivalent to -msg on. Virtual consoles only.

-powerdown [min]

Set the VESA powerdown interval to the specified number of minutes, from 0-60. If no value is specified for min, defaults to 0, disabling powerdown.

-powersave [mode]

Put the monitor in the specified VESA powersave mode. Specifying no mode is equivalent to off. The possible values of mode are:

on, vsync: vsynch suspend mode.
hsync: hsync suspend mode.
powerdown: Powerdown mode.
off: Turn off VESA powersaving features.

-regtabs [num]

Clear all existing tab stops and set a regular tab stop pattern at every num number (default 8). num is a number in the range 1-160. Virtual consoles only.

-repeat [on|off]

Turn keyboard repeat on or off. Virtual consoles only.

-reset

Display the terminal reset string to reset the terminal to its power-on state.

-reverse [on|off]

Turns reverse-video mode on or off. If the terminal is not a virtual console, -reverse off also turns off bold, half-bright, and blink modes.

-store

Store the current rendering options as the defaults. Virtual consoles only.

-tabs [tab1...tabn]

Set tab stops at the specified cursor positions, which can range from 1 to 160. Virtual consoles only.

-term term

Replace the value of the TERM environment variable with term.

-ulcolor 16-color

Set color for underlining. Virtual consoles only.

-underline [on|off]

Turn underlining on or off.

sftp

sftp [options] host

An interactive file transfer program, similar to ftp except that it uses ssh to perform file transfers securely. sftp connects to host and logs in, prompting for a password if required. The host can be specified in the following ways:

host
[user@]host[:file [file] ...]
[user@]host[:dir[/]]

If user is specified, that username is used for the login. If any files are specified, the sftp client automatically retrieves them after the user has been authenticated and then exits. If a directory dir is specified, the client starts in that directory on the remote host. sftp is part of the OpenSSH suite of network tools.

Options

-1: Use SSH1. The default is to use SSH2.
-b file: Run in batch mode, taking commands from the specified file. Requires the use of a noninteractive authentication mechanism.
-B bytes: Specify the size of the buffer sftp uses for file transfers. Default is 32768 bytes.
-C: Enable compression (uses ssh -C).
-F file: Use file as the ssh configuration file instead of the default system configuration file. The systemwide file is usually /etc/ssh/ssh_config and per-user files are $HOME/.ssh/config.
-ooption: Pass an option to ssh. The passed option is in the format used by ssh_config(5) (e.g., -oPORT=nn, where nn is the port number). -o can appear more than once to pass multiple options to ssh. This option is useful for passing options that don't have an equivalent sftp command-line option.
-P server_path: Connect directly to the local sftp server specified in server_path. Useful for debugging.
-R num: Specify the number of requests that may be outstanding at any time (default 16).
-s subsys|server_path: Specify the SSH2 subsystem or path to the sftp server on the remote system. Specifying the path is useful for using sftp via SSH1 or if the remote sshd does not have an sftp subsystem configured.
-S program: Specify the name of a program that understands ssh options and that you want to use for the encrypted connection.
-v: Raise the logging level.

sh [options] [file [arguments]]

The standard Unix shell, a command interpreter into which all other commands are entered. On Linux, this is just another name for the bash shell. For more information, see Chapter 7.

shar

shar [options] files
shar -S [options]

Create shell archives ("shar" files) that are in text format and can be mailed. These files may be unpacked later by executing them with /bin/sh. Other commands may be required on the recipient's system, such as compress, gzip, and uudecode. The resulting archive is sent to standard output unless the -o option is given.

Options

-a, --net-headers: Allows automatic generation of headers. The -n option is required if the -a option is used.
-b bits, --bits-per-code=bits: Use -b bits as a parameter to compress (when doing compression). Default value is 12. The -b option automatically turns on -Z.
-c, --cut-mark: Start the shar file with a line that says "Cut here."
-d delimiter, --here-delimiter=delimiter: Use delimiter for the files in the shar instead of SHAR_EOF.
-f, --basename: Causes only simple filenames to be used when restoring, which is useful when building a shar from several directories or another directory. (If a directory name is passed to shar, the substructure of that directory will be restored whether or not -f is used.)
-g level, --level-for-gzip=level: Use -level as a parameter to gzip (when doing compression). Default is 9. The -g option turns on the -z option by default.
--help: Print a help summary on standard output, then exit.
-l nn, --whole-size-limit=nn: Limit the output file size to nn kilobytes but don't split input files. Requires use of -o.
-m, --no-timestamp: Don't generate touch commands to restore the file modification dates when unpacking files from the archive.
-n name, --archive-name=name: Name of archive to be included in the header of the shar files. Required if the -a option is used.
--no-i18n: Do not produce internationalized shell archives; use default English messages. By default, shar produces archives that will try to output messages in the unpacker's preferred language (as determined by LANG/LC_MESSAGES).
-o prefix, --output-prefix=prefix: Save the archive to files prefix.01 through prefix.nn (instead of sending it to standard output). This option must be used when either -l or -L is used.
-p, --intermix-type: Allow positional parameter options. The options -B, -T, -z, and -Z may be embedded, and files to the right of the option will be processed in the specified mode.
--print-text-domain-dir: Print the directory shar looks in to find message files for different languages, then immediately exit.
-q, --quiet, --silent: Turn off verbose mode.
-s who@where, --submitter=who@where: Supply submitter name and address, instead of allowing shar to determine it automatically.
--version: Print the version number of the program on standard output, then exit.
-w, --no-character-count: Do not check each file with wc -c after unpacking. The default is to check.
-x, --no-check-existing: Overwrite existing files without checking. Default is to check and not overwrite existing files. If -c is passed as a parameter to the script when unpacking (sh archive -c), existing files will be overwritten unconditionally. See also -X.
-z, --gzip: gzip and uuencode all files prior to packing. Must be unpacked with uudecode and gunzip (or zcat).
-B, --uuencode: Treat all files as binary; use uuencode prior to packing. This increases the size of the archive, and it must be unpacked with uudecode.
-D, --no-md5-digest: Do not use md5sum digest to verify the unpacked files. The default is to check.
-F, --force-prefix: Force the prefix character to be prepended to every line even if not required. May slightly increase the size of the archive, especially if -B or -Z is used.
-L nn, --split-size-limit=nn: Limit output file size to nn kilobytes and split files if necessary. The archive parts created with this option must be unpacked in the correct order. Requires use of -o.
-M, --mixed-uuencode: Pack files in mixed mode (the default). Distinguishes files as either text or binary; binaries are uuencoded prior to packing.
-P, --no-piping: Use temporary files instead of pipes in the shar file.
-Q, --quiet-unshar: Disable verbose mode.
-S, --stdin-file-list: Read list of files to be packed from standard input rather than from the command line. Input must be in a form similar to that generated by the find command, with one filename per line.
-T, --text-files: Treat all files as text.
-V, --vanilla-operation: Produce shars that rely only upon the existence of sed and echo in the unsharing environment.
-X, --query-user: Prompt user to ask if files should be overwritten when unpacking.
-Z, --compress

showkey

showkey [options]

Print keycodes, scancodes, or ASCII codes of keys pressed on the keyboard. The default is to show keycodes. In keycode and scancode mode, the program terminates 10 seconds after the last key is pressed. In ASCII mode, press Ctrl-D to exit. This command may not function properly under the X Window System, which also reads from the console device.

Options

-a, --ascii: Print the ASCII character, decimal, octal, and hexadecimal values of keys pressed.
-h, --help: Print version number and help message, then exit.
-k, --keycodes: Print keycodes associated with key-press events. This is the default mode.
-s, --scancodes: Print the keyboard scancodes associated with key-press events.

showmount

showmount [options] [host]

NFS/NIS command. Show information about an NFS server. This information is maintained by the mountd server on host. The default value for host is the value returned by hostname. With no options, show the clients that have mounted directories from the host. showmount is usually found in /usr/sbin, which is not in the default search path.

Options

-a, --all: Print all remote mounts in the format hostname:directory, where hostname is the name of the client and directory is the root of the filesystem that has been mounted.
-d, --directories: List directories that have been remotely mounted by clients.
-e, --exports: Print the list of exported filesystems.
-h, --help: Provide a short help summary.
--no-headers: Do not print headers.
-v, --version: Report the current version of the program.

shred

shred [options] files

Overwrite a file to make the contents unrecoverable, and delete the file afterwards if requested.

Options

-: Shred standard output.
-f, --force: Force permissions to allow writing to files.
--help: Print help message and exit.
-nnum, --iterations=num: Overwrite files num times (default is 25).
-snum, --size=num: Shred num bytes. num can be expressed with suffixes (e.g., K, M, or G).
-u, --remove: Remove file after overwriting. shred does not remove the file unless this option is specified.
-v, --verbose: Verbose mode.
--version: Print version information and exit.
-x, --exact: Shred the exact file size; do not round up to the next full block.
-z, --zero: On the final pass, overwrite with zeros to hide the shredding.

shutdown

shutdown [options] when [message]

System administration command. Terminate all processing. when may be a specific time (in hh:mm format), a number of minutes to wait (in +m format), or now. A broadcast message notifies all users to log off the system. Processes are signaled with SIGTERM to allow them to exit gracefully. /etc/init is called to perform the actual shutdown, which consists of placing the system in runlevel 1. Only privileged users can execute the shutdown command, although init may call shutdown with root privileges when the CTRL-ALT-DEL key combination is pressed from the console keyboard. Broadcast messages, default or defined, are displayed at regular intervals during the grace period; the closer the shutdown time, the more frequent the message.

Options

-a: When called from init, shut down only if one of the users listed in the file /etc/shutdown.allow is currently logged in.
-c: Cancel a shutdown that is in progress.
-F: Force a filesystem check (fsck) on reboot.
-f: Reboot fast, by suppressing the normal call to fsck when rebooting.
-h: Halt the system when shutdown is complete.
-k: Print the warning message, but suppress actual shutdown.
-r: Reboot the system when shutdown is complete.
-t num: Ensure a num-second delay between killing processes and changing the runlevel.

size

size [options] [objfile...]

Print the number of bytes of each section of objfile and its total size. If objfile is not specified, a.out is used.

Options

-d: Display the size in decimal and hexadecimal.
--format=format: Imitate the size command from either System V (--format sysv) or BSD (--format berkeley).
--help: Print help message, then exit.
-o: Display the size in octal and hexadecimal.
--radix=num: Specify how to display the size: in hexadecimal and decimal (if num is 10 or 16) or hexadecimal and octal (if num is 8).
-t, --totals: Show object totals. Works only with Berkeley format listings.
--target=bfdname: Specify object format by binary file descriptor name. Use -h for a list of supported object formats.
-x: Display the size in hexadecimal and decimal.
-A: Imitate System V's size command.
-B: Imitate BSD's size command.
-V, --version: Print version, then exit.

skill

skill [signal] [options] processes
snice [priority] [options] processes

Send a signal to processes or reset the priority. The default signal for skill is TERM, and the default priority for snice is +4 but can be in the range +20 (slowest) to -20 (fastest). The selection options -c, -p, -t, and -u are not required, but can be specified to insure that processes are interpreted correctly.

Options

-c: The next argument is a command.
-i: Use interactive mode.
-l, -L: List available signals.
-n: Display the process ID, but take no other action.
-p: The next argument is a process ID.
-t: The next argument is a tty or pty.
-u: The next argument is a username.
-v: Verbose mode.

slattach

slattach [options] [tty]

TCP/IP command. Attach serial lines as network interfaces, thereby preparing them for use as point-to-point connections. Only a privileged user may attach or detach a network interface.

Options

-c command: Run command when the connection is severed.
-d: Debugging mode.
-e: Exit immediately after initializing the line.
-h: Exit when the connection is severed.
-l: Create UUCP-style lockfile in /var/spool/uucp.
-L: Enable three-wire operation.
-m: Suppress initialization of the line to 8-bit raw mode.
-n: Similar to mesg -n.
-p protocol: Specify protocol, which may be slip, adaptive, ppp, or kiss.
-q: Quiet mode; suppress messages.
-s speed: Specify line speed.

sleep

sleep amount[units]
sleep option

Wait a specified amount of time before executing another command. units may be s (seconds), m (minutes), h (hours), or d (days). The default for units is seconds.

Options

--help: Print usage information and exit.
--version: Print version information and exit.

snice

snice [priority] [options] processes

Reset the priority for processes. The default priority is +4. See skill for the possible options.

sort

sort [options] [files]

Sort the lines of the named files. Compare specified fields for each pair of lines; if no fields are specified, compare them by byte, in machine collating sequence. If no files are specified or if the file is -, the input is taken from standard input. See also uniq, comm, and join.

Options

-b, --ignore-leading-blanks: Ignore leading spaces and tabs.
-c, --check: Check whether files are already sorted and, if so, produce no output.
-d, --dictionary-order: Sort in dictionary order.
-f, --ignore-case: Fold; ignore uppercase/lowercase differences.
-g, --general-numeric-sort: Sort in general numeric order.
--help: Print a help message and then exit.
-i, --ignore-nonprinting: Ignore nonprinting characters (those outside ASCII range 040-176).
-n: Sort in arithmetic order.
-k n[,m], --key=n[,m]: Skip n-1 fields and stop at m-1 fields (i.e., start sorting at the nth field, where the fields are numbered beginning with 1).
-ofile: Put output in file.
-m, --merge: Merge already sorted input files.
-r, --reverse: Reverse the order of the sort.
-s, --stable: Stabilize sort by disabling last-resort comparison.
-tc, --field-separator=c: Separate fields with c (default is a tab).
-u, --unique: Identical lines in input file appear only one time in output.
-z, --zero-terminated: End lines with zero byte, not with newline.
--version: Print version information and then exit.
-M, --month-sort: Attempt to treat the first three characters as a month designation (JAN, FEB, etc.). In comparisons, treat JAN < FEB and any invalid name for a month as less than a valid month.
-Ssize, --buffer-size=size: Set the size of the main memory buffer to size, which may include a suffix; e.g., K (1024, the default) or M.
-T tempdir, --temporary-directory=dir: Directory pathname to be used for temporary files.

Examples

List files by decreasing number of lines:

wc -l * | sort -r

Alphabetize a list of words, remove duplicates, and print the frequency of each word:

sort -fd wordlist | uniq -c

Sort the password file numerically by the third field (user ID):

sort -nk3,4 -t: /etc/passwd

split

split [options] [infile [prefix]]

Split infile into equal-sized segments. infile remains unchanged, and the results are written to prefixaa, prefixab, and so on. The default prefix is x, giving the output files xaa, xab, etc. If infile is - or missing, standard input is read. See also csplit.

Options

-n

Split infile into n new files.

-a n, --suffix-length=n

Use suffixes of length n (default is 2).

-b n[b|k|m], --bytes=n[b|k|m]

Split infile into n-byte segments. Alternate blocksizes may be specified:

b: 512 bytes.
k: 1 kilobyte.
m: 1 megabyte.

-C bytes[b|k|m], --line-bytes=bytes[b|k|m]

Put a maximum of bytes into file; insist on adding complete lines.

-l n, --lines=n

Split infile into n-line segments (default is 1000).

--help

Print a message for each output file.

--verbose

--version

Take input from the standard input.

-

Examples

Break bigfile into 1000-line segments:

split bigfile

Join four files, then split them into 10-line files named new.aa, new.ab, and so on. Note that without the -, new. would be treated as a nonexistent input file:

cat list[1-4] | split -10 - new.

ssh

ssh [options] hostname [command]

Securely log a user into a remote system and run commands on that system. The version of ssh described here is the OpenSSH client. ssh can use either Version 1 (SSH1) or Version 2 (SSH2) of the SSH protocol. SSH2 is preferable, as it provides better encryption methods and greater connection integrity. The hostname can be specified either as hostname or as user@hostname. If a command is specified, the user is authenticated, the command is executed, and the connection is closed. Otherwise, a terminal session is opened on the remote system. See later under "Escape characters" for functions that can be supported through an escape character. The default escape character is a tilde (~). The exit status returned from ssh is the exit status from the remote system or 255 if there was an error.

Options

-1: Try only SSH1.
-2: Try only SSH2.
-4: Use only IPv4 addresses.
-6: Use only IPv6 addresses.
-a: Disable forwarding of the authentication agent connection.
-A: Allow forwarding of the authentication agent connection. Can also be specified on a per-host basis in a configuration file.
-b bind_address: Specify the interface to transmit from when there are multiple available interfaces or aliased addresses.
-c blowfish|3des|des|ciphers: Select the cipher for encrypting the session. The default is 3des. For SSH2, a comma-separated list of ciphers can also be specified, with the ciphers listed in order of preference. des is supported only for legacy SSH1 compatibility and otherwise should not be used.
-C: Enable compression. Useful mainly for slow connections. The default compression level can be set on a per-host basis in the configuration file with the CompressionLevel option.
-D port: Enable dynamic application-level port forwarding using port on the local side. Can be specified in the configuration file. Only root can forward privileged ports.
-e char|^char|none: Set the escape character (default ~). The escape character must be the first character on a line. If none is specified, disable the use of an escape character.
-f: Run interactively for user authentication, then go into background mode for command execution. Implies -n.
-F configfile: Specify a per-user configuration file (default is $HOME/.ssh/config).
-g: Allow remote hosts to connect to local forwarded ports.
-i idfile: Use idfile to read identity (private key) for RSA or DSA authentication. Default is $HOME/.ssh/id_rsa or $HOME/.ssh/id_dsa for SSH2, or $HOME/.ssh/identity for SSH1. You can specify more than one -i option on the command line or in the configuration file.
-I device: Specify a smartcard device from which to get the user's private RSA key.
-k: Disable Kerberos ticket and AFS token forwarding. Can be set on a per-host basis in the configuration file.
-l user: Log in as user on the remote system. Can be specified on a per-host basis in the configuration file.
-L port:host:hostport: Forward port on the local host to the specified remote host and port. Can be specified in the configuration file. Only root can forward privileged ports. For IPv6, an alternative syntax is port/host/hostport.
-m macspec: For SSH2, the contents of macspec specify message authentication code (MAC) algorithms to use. macspec is a comma-separated list of algorithms in order of preference.
-n: Get standard input as a redirection from /dev/null. Used to prevent reading from standard input, which is required when running ssh in the background. Useful for running X programs on a remote host.
-N: Do not execute a remote command. Useful with SSH2 for port forwarding.
-o option: Specify options in configuration-file format. Useful for specifying options that have no command-line equivalent.
-p port: Specify the port on the remote host to which ssh is to connect. Can be specified on a per-host basis in the configuration file.
-P: Use a nonprivileged port for outgoing connections. Useful if a firewall prevents connections from privileged ports.
-q: Run quietly, suppressing warnings and error messages.
-R port:host:hostport: Forward port on the remote host to the local host:hostport. Can be specified in the configuration file. You can forward privileged ports only if you are logged in as root on the remote host. For IPv6, an alternative syntax is port/host/hostport.
-s: For SSH2, request invocation of a subsystem on the remote host to be used for another application such as sftp. The desired subsystem is specified as the remote command.
-t: Force pseudo-tty allocation. Multiple -t options can be specified to force tty allocation even when ssh has no local tty.
-T: Disable pseudo-tty allocation.
-v: Verbose mode. Useful for debugging. Specify multiple -v options to increase verbosity.
-x: Disable X11 forwarding.
-X: Enable X11 forwarding. Can be specified on a per-host basis in the configuration file.

Escape characters

~.: Disconnect.
~~: Send a single ~.
~#: List forwarded connections.
~&: Run ssh in the background at logout, while waiting for a forwarded connection or X11 sessions to terminate.
~?: Display the available escape characters.
~C: Open a command line. Useful for adding port forwardings when using the -L and -R options.
~R: Request rekeying of the connection. Useful only for SSH2 and if the peer supports it.
~^Z: Suspend the connection.

Environment variables

DISPLAY: Set by SSH to hostname:n for forwarding X11 connections. hostname is the host where the shell is running and n is an integer greater than zero.
HOME: The path to the user's home directory.
LOGNAME: The same as USER; set only for compatibility with systems that use LOGNAME.
MAIL: The path to the user's mailbox.
PATH: The default PATH as specified when SSH was compiled.
SSH_ASKPASS: Can be set to the name of a program to run to open an X11 window and read the user's passphrase if ssh does not have an associated terminal.
SSH_AUTH_SOCK: The path of a Unix-domain socket for communicating with the agent.
SSH_CLIENT: Three space-separated values that contain the client IP address, the client port number, and the server port number.
SSH_ORIGINAL_COMMAND: The original command line, including arguments, if a forced command is executed.
SSH_TTY: The path to the tty device associated with the current shell or command. Not set if there is no associated tty.
TZ: The time zone, passed from the SSH daemon, if it was set when the daemon was started.
USER: The name of the user logging in.

Files

ssh uses the following files in the user's home directory:

$HOME/.rhosts: Lists host/user pairs allowed to log in. Used with rhosts authentication.
$HOME/.shosts: Like .rhosts, but allows rhosts authentication without permitting login with rlogin or rsh.
$HOME/.ssh/authorized_keys: Lists RSA/DSA public keys that can be used to log in as this user.
$HOME/.ssh/config: The user's configuration file.
$HOME/.ssh/environment: Additional environment variable definitions.
$HOME/.ssh/identity, $HOME/.ssh/id_dsa, $HOME/.ssh/id_rsa: The authentication identity of the user for SSH1 RSA, SSH2 DSA, and SSH2 RSA, respectively.
$HOME/.ssh/identity.pub, $HOME/.ssh/id_dsa.pub, $HOME/.ssh/id_rsa.pub: The public key for user authentication for SSH1 RSA, SSH2 DSA, and SSH2 RSA, respectively.
$HOME/.ssh/known_hosts: Contains host keys for all hosts the user has logged into that are not already in the systemwide file at /etc/ssh/ssh_known_hosts.
$HOME/.ssh/rc

ssh-add

ssh-add [options] [files]
ssh-add -e|-s reader

Add RSA or DSA identities to the authentication agent (see ssh-agent), which must be running and must be an ancestor of the current process. With no arguments specified, add the files $HOME/.ssh/id_rsa, $HOME/.ssh/id_dsa, and $HOME/.ssh/identity. If any files are specified, add those instead, prompting for a passphrase if required.

Options

-d: Remove an identity from the agent instead of adding one.
-D: Delete all identities from the agent.
-e reader: Remove key in specified smartcard reader.
-l: List fingerprints of all identities known to the agent.
-L: List public key parameters of all identities known to the agent.
-s: Add key in smartcard reader.
-t life: Set maximum lifetime when adding identities to an agent. The value of life can be in seconds or another time format specified in sshd.
-x: Lock the agent with a password.
-X: Unlock the agent.

ssh-agent

ssh-agent [options] [command [arguments]]

Hold private keys used for public key authentication. ssh-agent is usually executed at the beginning of an X or login session; then all other windows or programs given as command are run as clients of ssh-agent. When a command is specified, the command and any arguments are executed. The agent dies when the command completes. Use ssh-add to add keys to the agent. Operations that require a private key are performed by the agent, which returns the results to the requestor.

Options

-a bind_addr: Bind the agent to the socket bind_addr (default is /tmp/ssh-nnnnnnnn/agent, where nnnnnnnn is a generated number).
-c: Write csh commands to standard output. This is the default if the environment variable SHELL looks like a csh-type shell.
-d: Debug mode.
-k: Kill the current agent.
-s: Write Bourne shell commands to standard output. This is the default if the environment variable SHELL does not look like a csh-type command.

ssh-keygen

ssh-keygen [options]

Generate, manage, and convert authentication keys for ssh.

Options

-b bits: Specify the number of bits in the key. The minimum is 512 and the default is 1024.
-B: Show the bubblebabble digest (a digest represented as a string that looks like real words) for the private or public key file specified with -f.
-c: Change the comment in the private and public key files (for RSA1 keys only).
-C comment: Specify the new comment.
-D reader: Download the RSA public key from the smartcard in reader.
-e: Read an OpenSSH private or public key file and write it in SECSH Public Key File Format to standard output for exporting to a commercial SSH.
-f file: Specify the filename of the key file.
-i: Read an SSH2-compatible unencrypted private or public key file and write an OpenSSH-compatible key to standard output. Used to import keys from a commercial SSH.
-l: Show fingerprint of public or private RSA1 key file specified with -f.
-N passphrase: Specify the new passphrase.
-p: Change the passphrase for a private key file. Prompt for the file, the old passphrase, and twice for the new passphrase.
-P passphrase: Specify the old passphrase.
-q: Operate in quiet mode.
-t type: Specify the type of key to create. Possible values of type are rsa1 for SSH1, and rsa or dsa for SSH2.
-U reader: Upload an existing RSA private key to the smartcard in reader.
-y: Read a private OpenSSH-format file and print a public key to standard output.

ssh-keyscan

ssh-keyscan [options]

Gather public and private host keys from a number of hosts. Can be used in scripts.

Options

-4: Use IPv4 addresses only.
-6: Use IPv6 addresses only.
-f file: Read hostnames or addrlist namelist pairs from file. If - is specified instead of a filename, read hosts or addrlist namelist pairs from standard input.
-p port: Specify the port to connect to on the remote host.
-t type: Specify the type of key to get from the scanned hosts. Possible values are rsa1 for SSH1 (default) or rsa or dsa for SSH2. Specify multiple values in a comma-separated list.
-T timeout: Specify the timeout for attempting a connection, in seconds.
-v: Verbose mode.

sshd

sshd [options]

TCP/IP command. Server for the ssh program, providing a secure remote login and remote execution facility equivalent to rlogin and rsh. Normally started at boot, sshd listens for incoming connections, forking a new daemon when one is detected. The forked daemon handles authentication, command execution, and encryption. Most implementations of sshd support both SSH protocols 1 and 2. The following options are those used by OpenSSH, OpenBSD's Secure Shell implementation.

Options

-b bits: Use the specified number of bits in the server key. Default is 768.
-d: Run sshd in the foreground and send verbose debug information to the system log. Process only one connection. Use the specified number of bits in the server key. This option may be specified from one to three times. Each additional -d increases the level of information sent to the system log.
-e: Send output to standard error instead of the system log.
-f file: Read configuration information from file instead of the default configuration file /etc/ssh/sshd_config.
-g seconds: Set the grace time a client has to authenticate itself before the server disconnects and exits. The default is 600 seconds. A value of means there is no limit.
-h keyfile: Read the host's cryptographic key from the specified keyfile instead of from the default file /etc/ssh/ssh_host_key for SSH protocol 1, and the default files /etc/ssh/ssh_host_rsa_key and /etc/ssh/ssh_host_dsa_key for SSH protocol 2. The -h option may be given more than once to specify multiple keyfiles.
-i: Use when running sshd from inetd.
-k seconds: Set how often the version 1 server key should be regenerated. Default value is 3600 seconds. If set to 0 seconds, the key will never be regenerated.
-o setting: Pass a configuration file setting as an option.
-p port: Listen for connections on port. The default is 22. More than one -p option may be specified. This option overrides ports specified in a configuration file.
-q: Send no messages to the system log.
-t: Test configuration files and keys, then exit.
-u namelength: Specify the length of the remote hostname field in the UTMP structure as specifed in utmp.h. A namelength of 0 will cause sshd to write dotted decimal values instead of hostnames to the utmp file and prevent DNS requests unless required by the authentication mechanism.
-D: Do not detach from the foreground process.
-4: Use only IPv4 addresses.
-6: Use only IPv6 addresses.

stat

stat [options] files

Print out the contents of an inode as they appear to the stat system call in a human-readable format. The error messages "Can't stat file" and "Can't lstat file" usually mean the file doesn't exist. "Can't readlink file" generally indicates that something is wrong with a symbolic link.

Options

-c format: Display the output as specified by format.
-f: Display information about the filesystem where the file is located, not about the file itself.
-l: For links, display information about the files found by following the links.
-s: For SE (Security Enhanced) Linux, show security information, if it's available, in addition to stat's normal output.
-t: Print the output tersely, in a form suitable for parsing by other programs.
-v: Print version information and exit.

Output

stat and stat -l display the following:

Device number
Inode number
Access rights
Number of hard links
Owner's user ID and name, if available
Owner's group ID and name, if available
Device type for inode device
Total size, in bytes
Number of blocks allocated
I/O blocksize
Last access time
Last modification time
Last change time
Security context for SE Linux

If -f is specified, stat displays the following information about the filesystem:

Filesystem type
Filesystem blocksize
Total blocks in the filesystem
Number of free blocks
Number of free blocks for nonroot users
Total number of inodes
Number of free inodes
Maximum filename length

Format

The printf(3) flag characters #, 0, -, +, and space can be used in format. In addition, the field width and precision options can be used.

If -c format is specified, the following sequences can be used for format:

%a: Access rights in octal
%A: Access rights in human-readable form
%b: Number of blocks allocated
%c: SE Linux security context
%d: Device number in decimal
%D: Device number in hex
%f: Raw mode in hex
%F: File type
%g: Owner's group ID
%G: Owner's group name
%h: Number of hard links
%i: Inode number
%n: Filename
%N: Quoted filename. If file is a symbolic link, include path to original.
%o: I/O blocksize
%s: Total size, in bytes
%S: SE Linux SID (security identifier)
%t: Major device type in hex
%T: Minor device type in hex
%u: Owner's user ID
%U: Owner's username
%x: Last access time
%X: Last access time as seconds since the Epoch
%y: Last modification time (modification of the file contents)
%Y: Last modification time as seconds since the Epoch
%z: Time of last change (modification of the inode)
%Z: Time of last change as seconds since the Epoch

If both -c format and -f are specified, the following sequences can be used for format:

%a: Free blocks available to nonroot user
%b: Total data blocks in filesystem
%c: Total file nodes in filesystem
%d: Free file nodes in filesystem
%f: Free blocks in filesystem
%i: Filesystem ID, _ _val[0] in hex
%I: Filesystem ID, _ _val[1] in hex
%l: Maximum filename length
%n: Filename
%s: Optimal transfer blocksize
%t: Type in hex
%T: Type in human-readable form

Examples

Sample output from the command stat /:

stat /
  File: "/"
  Size: 4096            Blocks: 8          IO Block: 4096   Directory
Device: 303h/771d       Inode: 2           Links: 19
Access: (0755/drwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Access: Thu Jan  2 04:02:40 2003
Modify: Wed Jan  1 23:03:20 2003
Change: Wed Jan  1 23:03:20 2003

Sample output with -f, displaying information about the filesystem:

stat -f /
  File: "/"
    ID: 0        0        Namelen: 255     Type: ext2/ext3
Blocks: Total: 2612475    Free: 1869472    Available: 1736735    Size: 4096
Inodes: Total: 1329696    Free: 1150253

statd

rpc.statd [options]

System administration command. The NFS status server, statd, reports server status to clients like the rup command.

Options

-d: Debugging mode; log verbose information to standard error.
-F: Run statd in the foreground.
-n hostname, --name hostname: Specify a name to use for the local hostname. By default this is read using the gethostname function.
-o port, --outgoing-port port: Specify the port that statd should use for its outgoing requests to other servers. When not specified, a port is assigned by portmap.
-p port, --port port: Specify the incoming port that statd should listen on. When not specified, a port is assigned by portmap.
-V: Print version information, then exit.
-?: Print help message, then exit.

strace

strace [options] command [arguments]

Trace the system calls and signals for command and arguments. strace shows you how data is passed between the program and the system kernel. With no options, strace prints a line to stderr for each system call. It shows the call name, arguments given, return value, and any error messages generated. A signal is printed with both its signal symbol and a descriptive string.

Options

-a n: Align the return values in column n.
-c: Count all calls and signals and create a summary report when the program has ended.
-d: Debug mode. Print debugging information for strace on stderr.
-e [keyword=][!]values

strfile

strfile [options] input_file [output_file]
unstr [-c delimiter] input_file[.ext] [output_file]

strfile creates a random-access file for storing strings. The input file should be a file containing groups of lines separated by a line containing a single percent sign (or other specified delimiter character). strfile creates an output file that contains a header structure and a table of file offsets for each group of lines, allowing random access of the strings. The output file, if not specified on the command line, is named sourcefile.dat. unstr undoes the work of strfile, printing out the strings contained in the input file in the order they are listed in the header file data. If no output file is specified, unstr prints to standard output; otherwise, it prints to the file specified. unstr can also globally change the delimiter character in a strings file.

Options

Of the following options, only -c can be used with unstr. All other options apply only to strfile.

-c delimiter: Change the delimiting character from the percent sign to delimiter. Valid for both strfile and unstr.
-i: Ignore case when ordering the strings.
-o: Order the strings alphabetically.
-r: Randomize access to the strings.
-s: Run silently; don't give a summary message when finished.
-x: Set the STR_ROTATED bit in the header str_flags field.

strings

strings [options] files

Search each file specified and print any printable character strings found that are at least four characters long and followed by an unprintable character.

Options

-, -a, --all

Scan entire object files; default is to scan only the initialized and loaded sections for object files.

-e encoding, --encoding=encoding

Specify the character encoding of the strings to be found. Possible values are:

b: 16-bit big-endian
B: 32-bit big-endian
l: 16-bit little-endian
L: 32-bit little-endian
s: Single-byte character, such as ASCII, ISO-8859, etc. (the default)

-f, --print-file-name

Print the name of the file before each string.

-min-len, -n min-len, --bytes=min-len

Print only strings that are at least min-len characters.

-o

The same as -t o.

-t base, --radix=base

Print the offset within the file before each string, in the format specified by base:

d: Decimal
o: Octal
x: Hexadecimal

--target=format

Specify an alternative object code format to the system default. Valid targets include elf32-i386, a.out-i386-linux, efi-app-ia32, elf32-little, elf32-big, srec, symbolsrec, tekhex, binary, ihex, and trad-core.

--help

Print help message and then exit. The help message includes a list of valid targets.

-v, --version

Go through the entire login sequence (i.e., change to user's environment).

strip

strip [options] files

Remove symbols from object files, thereby reducing file sizes and freeing disk space.

Options

-Fbfdname, --target=bfdname: Specify object format for both input and output by binary file descriptor name bfdname. Use option -h to see a list of supported formats.
-I bfdname, --input-target=bfdname: Expect object format bfdname for input.
--help: Print help message, then exit.
-K symbol, --keep-symbol=symbol: Delete all symbols except the specified symbol. This option may be used more than once.
-N symbol, --strip-symbol=symbol: Remove symbol from the source file.
-O bfdname, --output-target=bfdname: Use object format bfdname for output.
-o file: Write stripped object to file instead of replacing the original. Only one object file at a time may be stripped when using this option.
-p, --preserve-dates: Preserve access and modification times.
-R section, --remove-section=section: Delete section.
-S, -g, -d, --strip-debug: Strip debugging symbols.
-s, --strip-all: Strip all symbols.
--strip-unneeded: Remove symbols not needed for relocation processing.
-V, --version: Print version and exit.
-v, --verbose: Verbose mode.
-X, --discard-locals: Strip local symbols that were generated by the compiler.
-x, --discard-all: Strip nonglobal symbols.

stty

stty [options] [modes]

Set terminal I/O options for the current standard input device. Without options, stty reports the terminal settings that differ from those set by running stty sane, where ^ indicates the Ctrl key and ^` indicates a null value. Most modes can be negated using an optional - (shown in brackets). The corresponding description is also shown in brackets. Some arguments use non-POSIX extensions; these are marked with *.

Options

-a, --all: Report all option settings.
-F, --device: Open the specified device and use it instead of standard input.
-g, --save: Report settings in stty-readable form (i.e., hex).
--help: Print help message and exit.
--version: Print version information and exit.

Control modes

n: Set terminal baud rate to n (e.g., 2400).
[-]clocal: [Enable] disable modem control.
[-]cread: [Disable] enable the receiver.
[-]crtscts*: [Disable] enable RTS/CTS handshaking.
csbits: Set character size to bits, which must be 5, 6, 7, or 8.
[-]cstopb: [1] 2 stop bits per character.
[-]hup: [Do not] hang up connection on last close.
[-]hupcl: Same as previous.
ispeed n: Set terminal input baud rate to n.
ospeed n: Set terminal output baud rate to n.
[-]parenb: [Disable] enable parity generation and detection.
[-]parodd: Use [even] odd parity.

Flow control modes

The following flow control modes are available by combining the ortsfl, ctsflow, and rtsflow flags:

Flag settings	Flow control mode
ortsfl rtsflow ctsflow	Enable unidirectional flow control.
ortsfl rtsflow -ctsflow	Assert RTS when ready to send.
ortsfl -rtsflow ctsflow	No effect.
ortsfl -rtsflow -ctsflow	Enable bidirectional flow control.
-ortsfl rtsflow ctsflow	Enable bidirectional flow control.
-ortsfl rtsflow -ctsflow	No effect.
-ortsfl -rtsflow ctsflow	Stop transmission when CTS drops.
-ortsfl -rtsflow -ctsflow	Disable hardware flow control.

Input modes

[-]brkint: [Do not] signal INTR on break.
[-]icrnl: [Do not] map CR to NL on input.
[-]ignbrk: [Do not] ignore break on input.
[-]igncr: [Do not] ignore CR on input.
[-]ignpar: [Do not] ignore parity errors.
[-]inlcr: [Do not] map NL to CR on input.
[-]inpck: [Disable] enable input parity checking.
[-]istrip: [Do not] strip input characters to 7 bits.
[-]iuclc*: [Do not] map uppercase to lowercase on input.
[-]ixany*: Allow [XON] any character to restart output.
[-]ixoff, [-]tandem: [Enable] disable sending of START/STOP characters.
[-]ixon: [Disable] enable XON/XOFF flow control.
[-]parmrk: [Do not] mark parity errors.
[-]imaxbel*: When input buffer is too full to accept a new character, [flush the input buffer] beep without flushing the input buffer.

Output modes

bsn: Select style of delay for backspaces (0 or 1).
crn: Select style of delay for carriage returns (0-3).
ffn: Select style of delay for formfeeds (0 or 1).
nln: Select style of delay for linefeeds (0 or 1).
tabn: Select style of delay for horizontal tabs (0-3).
vtn: Select style of delay for vertical tabs (0 or 1).
[-]ocrnl*: [Do not] map CR to NL on output.
[-]ofdel*: Set fill character to [NULL] DEL.
[-]ofill*: Delay output with [timing] fill characters.
[-]olcuc*: [Do not] map lowercase to uppercase on output.
[-]onlcr*: [Do not] map NL to CR-NL on output.
[-]onlret*: On the terminal, NL performs [does not perform] the CR function.
[-]onocr*: Do not [do] output CRs at column 0.
[-]opost: [Do not] postprocess output.

Local modes

[-]echo: [Do not] echo every character typed.
[-]echoe, [-]crterase: [Do not] echo ERASE character as BS-space-BS string.
[-]echok: [Do not] echo NL after KILL character.
[-]echonl: [Do not] echo NL.
[-]icanon: [Disable] enable canonical input (ERASE, KILL, WERASE, and RPRINT processing).
[-]iexten: [Disable] enable extended functions for input data.
[-]isig: [Disable] enable checking of characters against INTR, SUSPEND, and QUIT.
[-]noflsh: [Enable] disable flush after INTR or QUIT.
[-]tostop*: [Do not] send SIGTTOU when background processes write to the terminal.
[-]xcase*: [Do not] change case on local output.
[-]echoprt, [-]prterase*: When erasing characters, echo them backward, enclosed in \ and /.
[-]echoctl. [-]ctlecho*: Do not echo control characters literally. Use hat notation (e.g., ^Z).
[-]echoke [-]crtkill*: Erase characters as specified by the echoprt and echoe settings (default is echoctl and echok settings).

Control assignments

ctrl-char c: Set control character to c. ctrl-char is dsusp (flush input and then send stop), eof, eol, eol2 (alternate end-of-line), erase, intr, lnext (treat next character literally), kill, rprnt (redraw line), quit, start, stop, susp, swtch, or werase (erase previous word). c can be a literal control character, a character in hat notation (e.g., ^Z), in hex (must begin with 0x), in octal (must begin with 0), or in decimal. Disable the control character with values of ^- or undef.
min n: Set the minimum number of characters that will satisfy a read until the time value has expired when -icanon is set.
time n: Set the number of tenths of a second before reads time out if the min number of characters have not been read when -icanon is set.
line i*: Set line discipline to i (1-126).

Combination modes

[-]cooked: Same as [raw]-raw.
[-]evenp, [-]parity: Same as [-]parenb and cs[8]7.
[-]parity: Same as [-]parenb and cs[8]7.
ek: Reset ERASE and KILL characters to Ctrl-h and Ctrl-u, their defaults.
[-]lcase: [Unset] set xcase, iuclc, and olcuc.
[-]LCASE: Same as [-]lcase.
[-]nl: [Unset] set icrnl and onlcr. -nl also unsets inlcr, igncr, ocrnl, and onlret, icrnl, onlcr.
[-]oddp: Same as [-]parenb, [-]parodd, and cs7[8].
[-]raw: [Disable] enable raw input and output (no ERASE, KILL, INTR, QUIT, EOT, SWITCH, or output postprocessing).
sane: Reset all modes to reasonable values.
[-]tabs*: [Expand to spaces] preserve output tabs.
[-]cbreak: Same as [icanon]-icanon.
[-]pass8: Same as -parenb -istrip cs8.
[-]litout: Same as -parenb -istrip cs8.
[-]decctlq*: Same as -ixany.
crt: Same as echoe echoctl echoke.
dec: Same as echoe echoctl echoke -ixany. Additionally, set INTERRUPT to ^C, ERASE to DEL, and KILL to ^U.

Special settings

ispeed speed: Specify input speed.
ospeed speed: Specify output speed.
rows rows*: Specify number of rows.
cols columns, columns columns*: Specify number of columns.
size*: Display current row and column settings.
speed

su [option] [user] [shell_args]

Create a shell with the effective user ID user. If no user is specified, create a shell for a privileged user (i.e., become a superuser). Enter EOF to terminate. You can run the shell with particular options by passing them as shell_args (e.g., if the shell runs bash, you can specify -c command to execute command via bash, or -r to create a restricted shell).

Options

-, -l, --login

-c command, --command=command

Execute command in the new shell and then exit immediately. If command is more than one word, it should be enclosed in quotes. For example:

su -c 'find / -name \*.c -print' nobody

-f, --fast

Start the shell with the -f option, which suppresses the reading of the .cshrc or .tcshrc file. Applies to csh and tcsh.

-m, -p, --preserve-environment

Do not reset environment variables.

-s shell, --shell=shell

Execute shell, not the shell specified in /etc/passwd, unless shell is restricted.

--help

--version

Begin printing at nth item from end-of-file. k specifies the item to count: l (lines, the default), b (blocks), or c (characters).

sudo

sudo [options] [command]

If you are allowed, execute command as the superuser. Authorized users of sudo and the commands they are permitted to execute are listed in the sudo configuration file, /etc/sudoers. If an unauthorized user attempts to run a command, sudo will inform an administrator via email. By default, it will send the message to the root account. Users attempting to run commands are prompted for their password. Once authenticated, sudo sets a timestamp for the user. For five minutes from the timestamp, the user may execute further commands without being prompted for their password. This grace period may be overriden by settings in the /etc/sudoers file.

Options

-b: Execute command in the background.
-h: Print help message, then exit.
-k: Revoke user's sudo permissions. Similar to -K, but changes user's timestamp to the Epoch instead of revoking it.
-l: List all allowed and forbidden commands for the user on the current host, then exit.
-p promptstring: Use the specified promptstring to prompt for a password. The string may contain escape codes %u and %h, which will be replaced with the current user's login name and local hostname.
-s: Run the shell specified in the SHELL environment variable, or the default shell specified in /etc/passwd. If a command is given, it should be a shell script and not a binary file.
-u user: Run command as the specified user instead of the root user. This may also be specified as a user ID number using #uid.
-v: Update timestamp for user. Prompt for password if necessary.
-H: Set the HOME environment variable to the home directory of the target user.
-K: Remove user's timestamp.
-L: List parameters that may be set as defaults for a user in the /etc/sudoers file.
-P: Preserve initial user's group membership.
-S: Read password from standard input instead of from the console.
-V: Print version number, then exit. When run by the root user, print sudo's defaults and the local network address as well.
--: Stop reading command-line arguments.

sum

sum [options] files

Calculate and print a checksum and the number of (1KB) blocks for file. If no files are specified, or file is -, read from standard input. Useful for verifying data transmission.

Options

-r: The default setting. Use the BSD checksum algorithm.
-s, --sysv: Use alternate checksum algorithm as used on System V. The blocksize is 512 bytes.
--help: Print a help message and then exit.
--version: Print the version number and then exit.

swapoff

swapoff [options] [devicelist]

System administration command. Stop making devices and files specified in devicelist available for swapping and paging.

Option

-a: Consult /etc/fstab for devices marked sw. Use those in place of the device argument.
-h: Print help message and then exit.
-V: Display version number and then exit.

swapon

swapon [options] devices

System administration command. Make the listed devices available for swapping and paging.

Options

-a: Consult /etc/fstab for devices marked sw. Use those in place of the devices argument.
-e: Used with -a. Don't complain about missing devices.
-h: Print help message, then exit.
-p priority: Specify a priority for the swap area. Higher priority areas will be used up before lower priority areas are used.
-s: Print swap usage summaries, then exit.
-V: Print version information, then exit.

sync

sync

System administration command. Write filesystem buffers to disk. sync executes the sync( ) system call. If the system is to be stopped, sync must be called to ensure filesystem integrity. Note that shutdown automatically calls sync before shutting down the system. sync may take several seconds to complete, so the system should be told to sleep briefly if you are about to manually call halt or reboot. Note that shutdown is the preferred way to halt or reboot your system, as it takes care of sync-ing and other housekeeping for you.

sysctl

sysctl [options] [key]

System administration command. Examine or modify kernel parameters at runtime using the /proc/sys filesystem. While many of these kernel keys can be altered by other utilities, sysctl provides a single interface to kernel settings.

Options

-a, -A: Display all available values.
-e: Ignore requests for unknown keys.
-n: Do not print the keyname when printing values.
-p: Reset keys from information specified in /etc/sysctl.conf.
-w key=value: Write a new value to the specified key.

sysklogd

syslogd [options]

System administration command. sysklogd provides both syslogd and klogd functionality. By default, it is meant to behave exactly like the BSD version of syslogd. While the difference should be completely transparent to the user, sysklogd supports an extended syntax. It is invoked as syslogd.

sysklogd logs system messages into a set of files described by the configuration file /etc/syslog.conf. Each message is one line. A message can contain a priority code, marked by a number in angle brackets at the beginning of the line. Priorities are defined in <sys/syslog.h>. syslogd reads from an Internet domain socket specified in /etc/services. To bring syslogd down, send it a terminate signal. See also klogd.

Options

-a socket: Add socket to the list of sockets syslogd listens to.
-d: Turn on debugging.
-f configfile: Specify alternate configuration file.
-h: Forward messages from remote hosts to forwarding hosts.
-l hostlist: Specify hostnames that should be logged with just the hostname, not the fully qualified domain name. Multiple hosts should be separated by a colon (:).
-m markinterval: Select number of minutes between mark messages.
-n: Avoid auto-backgrounding. This is needed when starting syslogd from init.
-p socket: Send log to socket instead of /dev/log.
-r: Receive messages from the network using an Internet domain socket with the syslog service.
-s domainlist: Strip off domain names specified in domainlist before logging. Multiple domain names should be separated by a colon (:).
-v: Print version number, then exit.
-x: Disable domain name lookups for remote messages.

syslogd

syslogd

TCP/IP command. See sysklogd.

tac

tac [options] [file]

Named for the common command cat, tac prints files in reverse to standard output. Without a filename or with -, it reads from standard input. By default, tac reverses the order of the lines, printing the last line first.

Options

-b, --before: Print separator (by default a newline) before the string it delimits.
-r, --regex: Expect separator to be a regular expression.
-s string, --separator=string: Specify alternate separator (default is newline).
--help: Print a help message and then exit.
--version: Print version information and then exit.

tail

tail [options] [files]

Print the last 10 lines of each named file (or standard input if - is specified) on standard output. If more than one file is specified, the output includes a header at the beginning of each file:

=  =>filename<=  =

Options

-n[k]

-k

Same as -n, but use the default count of 10.

+n[k]

Like -n, but start at nth item from beginning of file.

+k

Like -k, but count from beginning of file.

-c num{bkm}, --bytes num{bkm}

Print last num bytes. An alternate blocksize may be specified:

b: 512 bytes
k: 1 kilobyte
m: 1 megabyte

-f, --follow[=name|descriptor]

Don't quit at the end of file; "follow" file as it grows and end when the user presses Ctrl-c. Following by file descriptor is the default, so -f, --follow, and --follow=descriptor are equivalent. Use --follow=name to track the actual name of a file even if the file is renamed, as with a rotated log file.

-F

Identical to --follow=name --retry.

--help

Print a help message and exit.

-n num, --lines=num

Print the last num lines.

--max-unchanged-stats=num

Used with --follow=name to reopen a file whose size hasn't changed after num iterations (default 5), to see if it has been unlinked or renamed (as with rotated log files).

--pid=pid

Used with -f to end when process ID pid dies.

-q, --quiet, --silent

Suppress filename headers.

--retry

With -f, keep trying to open a file even if it isn't accessible when tail starts or if it becomes inaccessible later.

-s sec, --sleep-interval=sec

With -f, sleep approximately sec seconds between iterations. Default is 1 second.

-v, --verbose

With multiple files, always output the filename headers.

--version

Set drive (0-7) and storage density (l, m, or h, corresponding to low, medium, or high). Not available in all versions of tar.

Examples

Show the last 20 lines containing instances of .Ah:

grep '\.Ah' file | tail -20

Show the last 10 characters of variable name:

echo "$name" | tail -c

Print the last two blocks of bigfile:

tail -2b bigfile

talk

talk person [ttyname]

Talk to another user. person is either the login name of someone on your own machine or user@host on another host. To talk to a user who is logged in more than once, use ttyname to indicate the appropriate terminal name. Once communication has been established, the two parties may type simultaneously, with their output appearing in separate windows. To redraw the screen, type Ctrl-L. To exit, type your interrupt character; talk then moves the cursor to the bottom of the screen and restores the terminal.

talkd

talkd [options]

TCP/IP command. Remote user communication server. talkd notifies a user that somebody else wants to initiate a conversation. A talk client initiates a rendezvous by sending a CTL_MSG of type LOOK_UP to the server. This causes the server to search its invitation tables for an existing invitation for the client. If the lookup fails, the caller sends an ANNOUNCE message, causing the server to broadcast an announcement on the callee's login ports requesting contact. When the callee responds, the local server responds with the rendezvous address, and a stream connection is established through which the conversation takes place.

Options

-d: Write debugging information to the syslogd log file.
-p: Log malformed packets to /var/log/talkd.packets.

tar

tar [options] [tarfile] [other-files]

Copy files to or restore files from an archive medium. If any files are directories, tar acts on the entire subtree. Options need not be preceded by - (though they may be). The exception to this rule is when you are using a long-style option (such as --modification-time). In that case, the exact syntax is:

tar --long-option -function-options files

For example:

tar --modification-time -xvf tarfile.tar

Function options

You must use exactly one of these, and it must come before any other options:

-c, --create: Create a new archive.
-d, --diff, --compare: Compare the files stored in tarfile with other-files. Report any differences: missing files, different sizes, different file attributes (such as permissions or modification time).
--delete: Delete from the archive. This option cannot be used with magnetic tape.
-r, --append: Append other-files to the end of an existing archive.
-t, --list: Print the names of other-files if they are stored on the archive (if other-files are not specified, print names of all files).
-u, --update: Add files if not in the archive or if modified.
-x, --extract, --get: Extract other-files from an archive (if other-files are not specified, extract all files).
-A, --catenate, --concatenate: Concatenate a second tar file to the end of the first.

Options

[drive][density]

--anchored

Exclude patterns must match the start of the filename (the default).

--atime-preserve

Preserve original access time on extracted files.

-b n, --blocking-factor=n

Set blocksize to n × 512 bytes.

--backup[=type]

Back up files rather than deleting them. If no backup type is specified, a simple backup is made with ~ as the suffix. (See also --suffix.) The possible values of type are:

t, numbered: Make numbered backups.
nil, existing: Make numbered backups if there are already numbered backups, otherwise make simple backups.
never, simple: Always make simple backups.

--checkpoint

List directory names encountered.

--exclude=pattern

Remove files matching pattern from any list of files.

-f file, --file=file

Store files in or extract files from archive file. Note that file may take the form hostname:filename.

--force-local

Interpret filenames in the form hostname:filename as local files.

-g file, --listed-incremental=file

Create new-style incremental backup.

--group=group

Use group as the group for files added to the archive.

-h, --dereference

Dereference symbolic links and archive the files they point to rather than the symbolic link.

--help

Print help message and exit.

-i, --ignore-zeros

Ignore zero-sized blocks (i.e., EOFs).

--ignore-case

Ignore case when excluding files.

--ignore-failed-read

Ignore unreadable files to be archived. Default behavior is to exit when encountering these.

-j, --bzip2, -i

Compress files with bzip2 before archiving them, or uncompress them with bunzip2 before extracting them.

-l, --one-file-system

Do not archive files from other filesystems.

-k, --keep-old-files

When extracting files, do not overwrite files with similar names. Instead, print an error message.

-m, --touch

Do not restore file modification times; update them to the time of extraction.

--mode=permissions

Use permissions when adding files to an archive. The permissions are specified the same way as for the chmod command.

--newer-mtime=date

Add only files whose contents have changed since date to the archive.

--no-anchor

Exclude patterns may match anything following a slash.

--no-ignore-case

Do not ignore case when excluding files.

--no-same-permissions

Do not extract permissions information when extracting files from the archive. This is the default for users, and therefore affects only the superuser.

--no-recursion

Do not move recursively through directories.

--no-same-owner

When extracting, create files with yourself as owner.

--no-wildcards

Don't use wildcards when excluding files; treat patterns as strings.

--no-wildcards-match-slash

Wildcards do not match slash when excluding files.

--null

Allow filenames to be null-terminated with -T. Override -C.

--numeric-owner

Use the numeric owner and group IDs rather than the names.

-o, --old-archive, --portability

Create old-style archive in Unix V7 rather than ANSI format.

--overwrite

Overwrite existing files and directory metadata when extracting from archive.

--overwrite-dir

Overwrite existing directory metadata when extracting from archive.

--owner=owner

Set owner as the owner of extracted files instead of the original owner. owner is first assumed to be a username, then, if there is no match, a numeric user ID.

-p, --same-permissions, --preserve-permissions

Keep permissions of extracted files the same as the originals.

--posix

Create a POSIX-compliant archive.

--preserve

Equivalent to invoking both the -p and -s options.

--record-size=size

Treat each record as having size bytes, where size is a multiple of 512.

--recursion

Move recursively through directories.

--recursive-unlink

Remove existing directory hierarchies before extracting directories with the same name.

--remove-files

Remove originals after inclusion in archive.

--rsh-command=command

Do not connect to remote host with rsh; instead, use command.

-s, --same-order, --preserve-order

When extracting, sort filenames to correspond to the order in the archive.

--same-owner

When extracting, create files with the same ownership as the originals.

--show-omitted-dirs

List directories being omitted when operating on an archive.

--suffix=suffix

Use suffix instead of the default ~ when creating a backup file.

--totals

Print byte totals.

--use-compress-program=program

Compress archived files with program, or uncompress extracted files with program.

-v, --verbose

Verbose. Print filenames as they are added or extracted.

--version

Print version information and exit.

--volno-file=file

Use/update the volume number in file.

-w, --interactive, --confirmation

Wait for user confirmation (y) before taking any actions.

--wildcards

Use wildcards when excluding files.

--wildcards-match-slash

Wildcards match / when excluding files.

-z, --gzip, --gunzip, --ungzip

Compress files with gzip before archiving them, or uncompress them with gunzip before extracting them.

-B, --read-full-records

Reblock while reading; used for reading from 4.2BSD pipes.

-C directory, --directory=directory

cd to directory before beginning tar operation.

-F script, --info-script=script, --new-volume-script=script

Implies -M (multiple archive files). Run script at the end of each file.

-G, --incremental

Create old-style incremental backup.

-K file, --starting-file=file

Begin tar operation at file in archive.

-L length, --tape-length=length

Write a maximum of length × 1024 bytes to each tape.

-M, --multivolume

Expect archive to be multivolume. With -c, create such an archive.

-N date, --newer=date, --after-date=date

Ignore files older than date.

-O, --to-stdout

Print extracted files to standard output.

-P, --absolute-names

Do not remove initial slashes (/) from input filenames.

-R, --block-number

Display archive's block number in messages.

-S, --sparse

Treat sparse files more efficiently when adding to archive.

-T file, --files-from=file

Consult file for files to extract or create.

-U, --unlink-first

Remove each existing file from the filesystem before extracting from the archive.

-V name, --label=name

Name this volume name.

-W, --verify

Check archive for corruption after creation.

-X file, --exclude-from file

Consult file for list of files to exclude.

-Z, --compress, --uncompress

Compress files with compress before archiving them, or uncompress them with uncompress before extracting them.

Examples

Create an archive of /bin and /usr/bin (c), show the command working (v), and store on the tape in /dev/rmt0:

tar cvf /dev/rmt0 /bin /usr/bin

List the tape's contents in a format like ls -l:

tar tvf /dev/rmt0

Extract the /bin directory:

tar xvf /dev/rmt0 /bin

Create an archive of the current directory and store it in a file backup.tar:

tar cvf - `find . -print` > backup.tar

(The - tells tar to store the archive on standard output, which is then redirected.)

tcpd

tcpd

TCP/IP command. Monitor incoming TCP/IP requests (such as those for telnet, ftp, finger, exec, rlogin). Provide checking and logging services; then pass the request to the appropriate daemon.

tcsh

tcsh [options] [file [arguments]]

An extended version of the C shell, a command interpreter into which all other commands are entered. For more information, see Chapter 8.

tee

tee [options] files

Accept output from another command and send it both to standard output and to files (like a T or fork in the road).

Options

-a, --append: Append to files; do not overwrite.
-i, --ignore-interrupts: Ignore interrupt signals.
--help: Print a help message and then exit.
--version: Print version information and then exit.

Example

s -l | tee savefile    View listing and save for later

telinit

telinit [option] [runlevel]

System administration command. Signal init to change the system's runlevel. telinit is actually just a link to init, the ancestor of all processes.

Option

-t seconds: Send SIGKILL seconds after SIGTERM. Default is 20.

Runlevels

The default runlevels vary from distribution to distribution, but these are standard:

0: Halt the system.
1, s, S: Single user.
6: Reboot the system.
a, b, c: Process only entries in /etc/inittab that are marked with runlevel a, b, or c.
q, Q: Reread /etc/inittab.

Check the /etc/inittab file for runlevels on your system.

telnet

telnet [options] [host [port]]

Access remote systems. telnet is the user interface that communicates with another host using the Telnet protocol. If telnet is invoked without host, it enters command mode, indicated by its prompt, telnet>, and accepts and executes the commands listed after the following options. If invoked with arguments, telnet performs an open command (shown in the following list) with those arguments. host indicates the host's official name, alias, or Internet address. port indicates a port number (default is the Telnet port).

The Telnet protocol is often criticized because it uses no encryption and makes it easy for snoopers to pick up user passwords. Most sites now use ssh instead.

Options

-a: Automatic login to the remote system.
-b hostalias: Use bind to bind the local socket to an aliased address or the address of an interface other than the one that would be chosen by connect.
-c: Disable reading of the user's .telnetrc file.
-d: Turn on socket-level debugging.
-e [escape_char]: Set initial telnet escape character to escape_char. If escape_char is omitted, no escape character is predefined.
-f: With Kerberos V5 authentication, allow forwarding of the local credentials to the remote system.
-k realm: With Kerberos authentication, obtain tickets for the remote host in realm, instead of in the remote host's realm.
-l user: When connecting to remote system and if remote system understands ENVIRON, send user to the remote system as the value for variable USER. Implies the -a option.
-n tracefile: Open tracefile for recording the trace information.
-r: Emulate rlogin. The default escape character for this mode is a tilde (~); an escape character followed by a dot causes telnet to disconnect from the remote host; a ^Z instead of a dot suspends telnet; and a ^] (the default telnet escape character) generates a normal telnet prompt. These codes are accepted only at the beginning of a line.
-x: Turn on datastream encryption if possible.
-8: Request 8-bit operation.
-E: Disable the escape character functionality.
-F: With Kerberos V5 authentication, allow local credentials to be forwarded to the remote system, including any that were already forwarded to the local environment.
-K: Do not allow automatic login to the remote system.
-L: Specify an 8-bit data path on output.
-X atype: Disable the atype type of authentication.

Commands

Ctrl-Z

Suspend telnet.

! [command]

Execute a single command in a subshell on the local system. If command is omitted, an interactive subshell will be invoked.

? [command]

Get help. With no arguments, print a help summary. If a command is specified, print the help information for just that command.

close

Close a Telnet session and return to command mode.

display argument ...

Display all or some of the set and toggle values.

environ [arguments [...]]

Manipulate variables that may be sent through the TELNET ENVIRON option. Valid arguments for environ are:

?: Get help for the environ command.
define variable value: Define variable to have a value of value.
undefine variable: Remove variable from the list of environment variables.
export variable: Mark variable to have its value exported to the remote side.
unexport variable: Mark variable to not be exported unless explicitly requested by the remote side.
list: Display current variable values.
send variable: Send the environment variable variable.

logout

If the remote host supports the logout command, close the telnet session.

mode [type]

Depending on state of Telnet session, type is one of several options:

?: Print out help information for the mode command.
character: Disable TELNET LINEMODE option, or, if remote side does not understand the option, enter "character-at-a-time" mode.
[-]edit: Attempt to [disable] enable the EDIT mode of the TELNET LINEMODE option.
[-]isig: Attempt to [disable] enable the TRAPSIG mode of the LINEMODE option.
line: Enable LINEMODE option, or, if remote side does not understand the option, enter "old line-by-line" mode.
[-]softtabs: Attempt to [disable] enable the SOFT_TAB mode of the LINEMODE option.
[-]litecho: [Disable] enable LIT_ECHO mode.

open[-l user] host [port]

Open a connection to the named host. If no port number is specified, attempt to contact a Telnet server at the default port.

quit

Close any open Telnet session and then exit telnet.

send arguments

Send one or more special character sequences to the remote host. Following are the arguments that may be specified:

?: Print out help information for send command.
abort: Send Telnet ABORT sequence.
ao: Send Telnet AO sequence, which should cause the remote system to flush all output from the remote system to the user's terminal.
ayt: Send Telnet AYT (Are You There) sequence.
brk: Send Telnet BRK (Break) sequence.
do cmd
dont cmd
will cmd
wont cmd: Send Telnet DO cmd sequence, where cmd is a number between 0 and 255 or a symbolic name for a specific telnet command. If cmd is ? or help, this command prints out help (including a list of symbolic names).
ec: Send Telnet EC (Erase Character) sequence, which causes the remote system to erase the last character entered.
el: Send Telnet EL (Erase Line) sequence, which causes the remote system to erase the last line entered.
eof: Send Telnet EOF (End Of File) sequence.
eor: Send Telnet EOR (End Of Record) sequence.
escape: Send current Telnet escape character (initially ^]).
ga: Send Telnet GA (Go Ahead) sequence.
getstatus: If the remote side supports the Telnet STATUS command, getstatus sends the subnegotiation request that the server send its current option status.
ip: Send Telnet IP (Interrupt Process) sequence, which causes the remote system to abort the currently running process.
nop: Send Telnet NOP (No Operation) sequence.
susp: Send Telnet SUSP (Suspend Process) sequence.
synch: Send Telnet SYNCH sequence, which causes the remote system to discard all previously typed (but not read) input.

set argument value

unset argument value

Set any one of a number of telnet variables to a specific value or to TRUE. The special value off disables the function associated with the variable. unset disables any of the specified functions. The values of variables may be interrogated with the aid of the display command. The variables that may be specified are:

?: Display legal set and unset commands.
ayt: If telnet is in LOCALCHARS mode, this character is taken to be the alternate AYT character.
echo: This is the value (initially ^E) that, when in "line-by-line" mode, toggles between doing local echoing of entered characters and suppressing echoing of entered characters.
eof: If telnet is operating in LINEMODE or in the old "line-by-line" mode, entering this character as the first character on a line will cause the character to be sent to the remote system.
erase: If telnet is in LOCALCHARS mode and operating in the "character-at-a-time" mode, entering this character will send a Telnet EC sequence to the remote system.
escape: This is the Telnet escape character (initially ^]), which causes entry into the Telnet command mode when connected to a remote system.
flushoutput: If telnet is in LOCALCHARS mode and the flushoutput character is entered, a Telnet AO sequence is sent to the remote host.
forw1: If Telnet is in LOCALCHARS mode, this character is taken to be an alternate end-of-line character.
forw2: If Telnet is in LOCALCHARS mode, this character is taken to be an alternate end-of-line character.
interrupt: If Telnet AO is in LOCALCHARS mode and the interrupt character is entered, a Telnet IP sequence is sent to the remote host.
kill: If Telnet IP is in LOCALCHARS mode and operating in the "character-at-a-time" mode, entering this character causes a Telnet EL sequence to be sent to the remote system.
lnext: If Telnet EL is in LINEMODE or the old "line-by-line" mode, this character is taken to be the terminal's lnext character.
quit: If Telnet EL is in LOCALCHARS mode and the quit character is entered, a Telnet BRK sequence is sent to the remote host.
reprint: If Telnet BRK is in LINEMODE or the old "line-by-line" mode, this character is taken to be the terminal's reprint character.
rlogin: Enable rlogin mode. Same as using the -r command-line option.
start: If the Telnet TOGGLE-FLOW-CONTROL option has been enabled, this character is taken to be the terminal's start character.
stop: If the Telnet TOGGLE-FLOW-CONTROL option has been enabled, this character is taken to be the terminal's stop character.
susp: If Telnet is in LOCALCHARS mode or if the LINEMODE is enabled, the suspend character causes a Telnet SUSP sequence to be sent to the remote host.
tracefile: This is the file to which output generated by netdata is written.
worderase: If Telnet BRK is in LINEMODE or the old "line-by-line" mode, this character is taken to be the terminal's worderase character. Defaults for these are the terminal's defaults.

slc [state]

Set state of special characters when Telnet LINEMODE option has been enabled.

?: List help on the slc command.
check: Verify current settings for current special characters. If discrepancies are discovered, convert local settings to match remote ones.
export: Switch to local defaults for special characters.
import: Switch to remote defaults for special characters.

status

Show current status of telnet. This includes the peer you are connected to as well as the current mode.

toggle arguments [...]

Toggle various flags that control how Telnet responds to events. The flags may be set explicitly to true or false using the set and unset commands listed previously. The valid arguments are:

?: Display legal toggle commands.
autoflush: If autoflush and LOCALCHARS are both true, then when the ao or quit characters are recognized, Telnet refuses to display any data on the user's terminal until the remote system acknowledges that it has processed those Telnet sequences.
autosynch: If autosynch and LOCALCHARS are both true, then when the intr or quit character is entered, the resulting Telnet sequence sent is followed by the Telnet SYNCH sequence. Initial value for this toggle is false.
binary: Enable or disable the Telnet BINARY option on both the input and the output.
inbinary: Enable or disable the Telnet BINARY option on the input.
outbinary: Enable or disable the Telnet BINARY option on the output.
crlf: If this toggle value is true, carriage returns are sent as CR-LF. If false, carriage returns are sent as CR-NUL. Initial value is false.
crmod: Toggle carriage return mode. Initial value is false.
debug: Toggle socket-level debugging mode. Initial value is false.
localchars: If the value is true, flush, interrupt, quit, erase, and kill characters are recognized locally, then transformed into appropriate Telnet control sequences. Initial value is true.
netdata: Toggle display of all network data. Initial value is false.
options: Toggle display of some internal telnet protocol processing that pertains to Telnet options. Initial value is false.
prettydump: When netdata and prettydump are enabled, the output from the netdata command is reorganized into a more user-friendly format, spaces are put between each character in the output, and an asterisk precedes any Telnet escape sequence.
skiprc: Toggle whether to process ~/.telnetrc file. Initial value is false, meaning the file is processed.
termdata: Toggle printing of hexadecimal terminal data. Initial value is false.

Suspend telnet; works only for tcsh.

telnetd

telnetd [options]

TCP/IP command. Telnet protocol server. telnetd is invoked by the Internet server for requests to connect to the Telnet port (port 23 by default). telnetd allocates a pseudo-terminal device for a client, thereby creating a login process that has the slave side of the pseudo-terminal serving as stdin, stdout, and stderr. telnetd manipulates the master side of the pseudo-terminal by implementing the Telnet protocol and by passing characters between the remote client and the login process.

The Telnet protocol is often criticized because it uses no encryption and makes it easy for snoopers to pick up user passwords. Most sites now use ssh instead.

Options

-a type

When compiled with authentication support, this option sets the authentication type. Accepted values are:

debug: Debug authentication code.
user: Allow only authenticated remote users with permission to access their accounts without giving a password.
valid: Allow only authenticated remote users. Use login for any additional verification needed to access an account.
none: No authentication required, but accept it if offered. Use login for any further verification needed to access an account.
off: Disable authentication.

-debug [port]

Start telnetd manually instead of through inetd. port may be specified as an alternate TCP port number on which to run telnetd.

-D modifier(s)

Debugging mode. This allows telnet to print out debugging information to the connection, enabling the user to see what telnet is doing. Several modifiers are available for the debugging mode:

netdata: Display data stream received by telnetd.
options: Print information about the negotiation of the Telnet options.
ptydata: Display data written to the pseudo-terminal device.
report: Print options information, as well as some additional information about what processing is going on.

-edebug

When compiled with support for encryption, enable encryption debugging code.

-h

Don't print host-specific information until after login is complete.

-L command

Use command for login instead of /bin/login.

-n

Disable checking for lost connections with TCP keep-alives.

-X type

Disable authentication type.

test

test expression 
[expression]

Evaluate an expression and, if its value is true, return a zero exit status; otherwise, return a nonzero exit status. In shell scripts, you can use the alternate form [expression]. This command is generally used with conditional constructs in shell programs. Also exists as a built-in in most shells.

File testers

The syntax for all of these options is test option file. If the specified file does not exist, they return false. Otherwise, they test the file as specified in the option description.

-b: Is the file block special?
-c: Is the file character special?
-d: Is the file a directory?
-e: Does the file exist?
-f: Is the file a regular file?
-g: Does the file have the set-group-ID bit set?
-k: Does the file have the sticky bit set?
-L: Is the file a symbolic link?
-p: Is the file a named pipe?
-r: Is the file readable by the current user?
-s: Is the file nonempty?
-S: Is the file a socket?
-t [file-descriptor]: Is the file associated with file-descriptor (or 1, standard output, by default) connected to a terminal?
-u: Does the file have the set-user-ID bit set?
-w: Is the file writable by the current user?
-x: Is the file executable?
-O: Is the file owned by the process's effective user ID?
-G: Is the file owned by the process's effective group ID?

File comparisons

The syntax for file comparisons is test file1 option file2. A string by itself, without options, returns true if it's at least one character long.

-nt: Is file1 newer than file2? Check modification date, not creation date.
-ot: Is file1 older than file2? Check modification date, not creation date.
-ef: Do the files have identical device and inode numbers?

String tests

The syntax for string tests is test option string or test string1 [!]= string2.

-z: Is the string 0 characters long?
-n: Is the string at least 1 character long?
string1 = string2: Are the two strings equal?
string1 != string2: Are the strings unequal?

Expression tests

Note that an expression can consist of any of the previous tests.

! expression: Is the expression false?
expression -a expression: Are the expressions both true?
expression -o expression: Is either expression true?

Integer tests

The syntax for integer tests is test integer1 option integer2. You may substitute -l string for an integer; this evaluates to string's length.

-eq: Are the two integers equal?
-ne: Are the two integers unequal?
-lt: Is integer1 less than integer2?
-le: Is integer1 less than or equal to integer2?
-gt: Is integer1 greater than integer2?
-ge: Is integer1 greater than or equal to integer2?

tftp

tftp [options] [host [port]]

User interface to TFTP (IPv4 Trivial File Transfer Protocol), which allows users to transfer files to and from a remote machine. The remote host may be specified, and optionally the port, in which case tftp uses host as the default host for future transfers. The version of tftp described here is tftp-hpa.

Options

-v: Verbose mode.
-V: Print version and configuration information and exit.

Commands

Once tftp is running, it issues the prompt:

tftp>

and recognizes the following commands:

? [command...]
help [command...]: Print help information. If no command is specified, list the commands and a brief usage message. With a command, list the usage message for that command.
ascii: Shorthand for mode ascii.
binary: Shorthand for mode binary.
connect hostname [port]: Set the hostname, and optionally the port, for transfers.
get filename
get remotename localname
get filename1 filename2 filename3...filenameN: Get a file or set of files from the specified remote sources. The filename can be specified as host:filename to set both host and filename at the same time. In that case, the last host specified becomes the default for future file transfers.
mode transfer-mode: Set the mode for transfers. transfer-mode may be ascii, netascii, binary, octet, or image. The default is ascii.
put filename
put localfile remotefile
put filename1 filename2...filenameN remote-directory: Transfer a file or set of files to the specified remote file or directory. The destination can be specified as host:filename to set both host and filename at the same time. In that case, the last host specified becomes the default for future file transfers. If remote-directory is specified, the remote host is assumed to be a Unix-style system that uses / as the directory path separator.
quit: Exit tftp.
rexmt retransmission-timeout: Set the per-packet retransmission timeout, in seconds.
status: Print status information: whether tftp is connected to a remote host (i.e., whether a host has been specified for the next connection), the current mode, whether verbose and tracing modes are on, and the values for retransmission timeout and total transmission timeout.
timeout total-transmission-timeout: Set the total transmission timeout, in seconds.
trace: Toggle packet tracing.
verbose: Toggle verbose mode.

tftpd

in.tftpd [options] [directories]

TCP/IP command. IPv4 Trivial File Transfer Protocol server. in.tftpd is normally started by inetd and operates at the port indicated in the tftp Internet service description in /etc/services. Only publicly readable files may be accessed. By default, only files that already exist and are publicly writable can be written. In addition, if any directories are specified, access is restricted to files in those directories. The version of tftp described here is tftp-hpa.

Options

-a [address][:port]: Specify the address and port to listen to when run in standalone mode with -l. By default, use the address and port in /etc/services.
-c: Allow new files to be written. The default permissions allow anyone to read and write the files. Use -p or -U to set other permissions.
-l: Run tftpd in standalone mode, not from inetd. This mode ignores -t.
-m remap-file: Remap filenames based on rules specified in remap-file. Each line in the file contains an operation, an egrep-style regular expression (regex), and optionally a replacement pattern. If the regex matches any part of a filename, the operation is performed. The operation is specified as any of the letters shown in the next section, alone or in combination. Comment lines begin with #.
-p: Use only normal system access controls for the user specified with -u (the tftpd username).
-r option: Never accept the specified RFC 2347 option (see the later section "Standards"). The possible options are blksize, blksize2 (not based on a standard; like blksize but the blocksize must be a power of 2), tsize (transfer size), and timeout.
-s: On startup, change root directory to the directory specified as directory on the command line. With -s, only one directory should be specified. Recommended for security and compatibility with certain boot ROMs.
-t timeout: When run from inetd, specify how long, in seconds, to wait for another connection before timing out and terminating the server. Default timeout is 900 (15 minutes). If server is terminated, inetd spawns a new server on receiving a new request.
-u username: Specify the name of the tftpd user. The default user is nobody.
-U umask: Set the umask for newly created files. Without -p, the default is 0. With -p, it is inherited from the calling process.
-v: Increase verbosity. Specify multiple times for greater verbosity.
-V: Print version and configuration information and exit.

Filename remapping rules

a: If this rule matches, refuse the request and send an "access denied" error to the client.
e: If this rule matches, execute it and then end rule processing.
g: Repeat the rule until it no longer matches. Used with r.
G: Apply this rule to GET (RRQ) requests only.
i: Use case-insensitive regex matching. The default is for case-sensitive matching.
P: Apply this rule to PUT (WRQ) requests only.
r: Replace the matching substring with the replacement pattern.
s: If this rule matches, execute it and then restart rule processing with the first rule.

The replacement pattern can include the following escape sequences:

\0: The entire string matching the regex.
\1...\9: The strings matched by each of the first nine substrings in the regex.
\i: The IP address of the requesting host, in dotted-quad notation.
\x: The IP address of the requesting host, in hexadecimal notation.
\\: Literal backslash.
\whitespace: Literal whitespace.
\#: Literal hash mark.

Standards

RFC 1123, Requirements for Internet Hosts--Application and Support
RFC 1350, The TFTP Protocol (Revision 2)
RFC 2347, TFTP Option Extension
RFC 2348, TFTP Blocksize Option
RFC 2349, TFTP Timeout Interval and Transfer Size Options

time

time [options] command [arguments]

Run the specified command, passing it any arguments, and time the execution. Note that there is also a shell time command, so you might need to specify the full path, usually /usr/bin/time, to run this version of time. time displays its results on standard error. The output includes elapsed time, user CPU time, system CPU time, and other information such as memory used and number of I/Os. The output can be formatted using printf format strings specified with the -f option or the TIME environment variable.

Options

--: The end of the options. Anything after the -- is the command or one of its arguments.
-a, --append: Used with -o to append the output to file instead of overwriting it.
-f format, --format=format: Specify the output format. Overrides any format specified in the TIME environment variable.
--help: Print help message and exit.
-o file, --output=file: Send the output from time to the specified file instead of to standard error. If file exists, it is overwritten.
-p, --portability: Use portable output format (POSIX).
-v, --verbose: Give verbose output, providing all available information.
-V, --version: Print version information and exit.

Resources

The following resources can be specified in format strings:

c: Number of involuntary context switches because of time slice expiring.
C: Name and arguments of command being timed.
D: Average size of unshared data area, in kilobytes.
e: Elapsed real time, in seconds.
E: Elapsed real time as hours:minutes:seconds.
F: Number of major (I/O-requiring) page faults.
I: Number of filesystem inputs.
k: Number of signals delivered to the process.
K: Average total (data+stack+text) memory use, in kilobytes.
M: Maximum resident set size, in kilobytes.
O: Number of filesystem outputs.
p: Average unshared stack size, in kilobytes.
P: Percent of CPU used.
r: Number of socket messages received.
R: Number of minor (recoverable) page faults.
s: Number of socket messages received.
S: Total CPU seconds used by the system on behalf of the process.
t: Average resident set size, in kilobytes.
U: Total CPU seconds used directly by the process.
w: Number of voluntary context switches.
W: Number of times the process was swapped out of main memory.
x: Exit status of the command.
X: Average shared text size, in kilobytes.
Z: System page size, in bytes.

Example

Time the execution of the command ls -l and display the user time, system time, and exit status of the command:

/usr/bin/time -f "\t%U user,\t%S system,\t%x status" ls -Fs

tload

tload [options] [tty]

Display system load average in graph format. If tty is specified, print it to that terminal.

Options

-d delay: Specify the delay, in seconds, between updates.
-s scale: Specify scale (number of characters between each graph tick). A smaller number results in a larger scale.
-V: Print version information and exit.

top

top [options]

Provide information (frequently refreshed) about the most CPU-intensive processes currently running. You do not need to include a - before options. See ps for explanations of the field descriptors.

Options

-b: Run in batch mode; don't accept command-line input. Useful for sending output to another command or to a file.
-c: Show command line in display instead of just command name.
-C: For SMP systems, display total CPU information in addition to information for the individual CPUs.
-d delay: Specify delay between refreshes.
-h: Print a help message and exit.
-i: Suppress display of idle and zombie processes.
-n num: Update display num times, then exit.
-p pid: Monitor only processes with the specified process ID.
-q: Refresh without any delay. If user is privileged, run with highest priority.
-s: Secure mode. Disable some (dangerous) interactive commands.
-S: Cumulative mode. Print total CPU time of each process, including dead child processes.
-v: Print version information and exit.

Interactive commands

space: Update display immediately.
c: Toggle display of command name or full command line.
f, F: Add fields to or remove fields from the display.
h, ?: Display help about commands and the status of secure and cumulative modes.
H: Prompt for a process ID and show all threads for that process.
k: Prompt for process ID to kill and signal to send (default is 15) to kill it.
i: Toggle suppression of idle and zombie processes.
l: Toggle display of load average and uptime information.
m: Toggle display of memory information.
n, #: Prompt for number of processes to show. If 0 is entered, show as many as will fit on the screen (default).
o, O: Change order of displayed fields.
q: Exit.
r: Apply renice to a process. Prompt for PID and renice value. Suppressed in secure mode.
s: Change delay between refreshes. Prompt for new delay time, which should be in seconds. Suppressed in secure mode.
t: Toggle display of processes and CPU states lines.
A: Sort by age, with newest first.
^L: Redraw screen.
M: Sort tasks by resident memory usage.
N: Sort numerically by process ID.
P: Sort tasks by CPU usage (default).
S: Toggle cumulative mode. (See the -S option.)
T: Sort tasks by time/cumulative time.
W: Write current setup to ~/.toprc. This is the recommended way to write a top configuration file.

Field descriptions

The first five entries in the following list describe the lines that appear at the top of the top display. The rest are the fields that can be displayed for each task (sizes are in kilobytes). Use the interactive f command to add or remove fields.

uptime: Display the time the system has been up, and three load averages consisting of the average number of processes ready to run in the last 1, 5, and 15 minutes.
processes: The total number of processes running when the last update was taken, shown as the number of running, sleeping, stopped, or undead tasks.
CPU states: The percentage of CPU time spent in user mode, in system mode, on tasks with a negative nice value, and idle.
Mem: Memory statistics, including total available memory, free memory, memory used, shared memory, and memory used for buffers.
Swap: Swap-space statistics, including total, available, and used.
PID: Process ID.
PPID: Parent process ID.
UID: User ID of task's owner.
USER: Username of task's owner.
PRI: Priority.
NI: Nice value.
PAGEIN: Page fault count.
SIZE: Total size of the task's code, data, and stack space.
TSIZE: Code size.
DSIZE: Data plus stack size.
TRS: Resident text size.
SWAP: Size of swapped-out portion of task.
D: Size of pages marked dirty.
LC: Last-used processor, for multiprocessor systems.
RSS: Total amount of physical memory used.
SHARE: Amount of shared memory used.
STAT: State of the task. Values are S (sleeping), D (uninterruptible sleep), R (running), Z (zombies), or T (stopped or traced), possibly followed by < (negative nice value), N (positive nice value), or W (swapped out).
WCHAN: Address or name of the kernel function in which the task is currently sleeping.
TIME: Total CPU time used by task and any children.
%CPU: Share of CPU time since last update, as percentage of total CPU time.
%MEM: Share of physical memory.
TTY: Controlling tty.
COMMAND: Command line (truncated if too long) if task is in memory, or command name in parentheses if swapped out.
FLAGS

touch

touch [options] files

For one or more files, update the access time and modification time (and dates) to the current time and date. touch is useful in forcing other commands to handle files a certain way; for example, the operation of make, and sometimes find, relies on a file's access and modification time. If a file doesn't exist, touch creates it with a filesize of 0.

Options

-a, --time=atime, --time=access, --time=use: Update only the access time.
-c, --no-create: Do not create any file that doesn't already exist.
-d time, --date time: Change the time value to the specified time instead of the current time. time can use several formats and may contain month names, time zones, a.m. and p.m. strings, etc.
-m, --time=mtime, --time=modify: Update only the modification time.
-r file, --reference file: Change times to be the same as those of the specified file, instead of the current time.
-t time: Use the time specified in time instead of the current time. This argument must be of the format [[cc]yy]mmddhhmm[.ss], indicating optional century and year, month, date, hours, minutes, and optional seconds.
--help: Print help message and then exit.
--version: Print the version number and then exit.

tr [options] [string1 [string2]]

Translate characters. Copy standard input to standard output, substituting characters from string1 to string2 or deleting characters in string1.

Options

-c, --complement: Complement characters in string1 with respect to ASCII 001-377.
-d, --delete: Delete characters in string1 from output.
-s, --squeeze-repeats: Squeeze out repeated output characters in string2.
-t, --truncate-set1: Truncate string1 to the length of string2 before translating.
--help: Print help message and then exit.
--version: Print the version number and then exit.

Special characters

Include brackets ([ ]) where shown.

\a

\b

\f

\n

\r

\t

\v

\nnn

Character with octal value nnn

\\

Literal backslash

char1-char2

All characters in the range char1 through char2. If char1 does not sort before char2, produce an error.

[char*]

In string2, expand char to the length of string1.

[char*number]

Expand char to number occurrences. [x*4] expands to xxxx, for instance.

[:class:]

Expand to all characters in class, where class can be:

alnum: Letters and digits
alpha: Letters
blank: Whitespace
cntrl: Control characters
digit: Digits
graph: Printable characters except space
lower: Lowercase letters
print: Printable characters
punct: Punctuation
space: Whitespace (horizontal or vertical)
upper: Uppercase letters
xdigit: Hexadecimal digits

[=char=]

The class of characters to which char belongs.

Examples

Change uppercase to lowercase in a file:

cat file | tr 'A-Z' 'a-z'

Turn spaces into newlines (ASCII code 012):

tr ' ' '
' < file

Strip blank lines from file and save in new.file (or use 011 to change successive tabs into one tab):

cat file | tr -s "" "
" > new.file

Delete colons from file and save result in new.file:

tr -d : < file > new.file

traceroute

traceroute [options] host [packetsize]

TCP/IP command. Trace route taken by packets to reach network host. traceroute attempts tracing by launching UDP probe packets with a small TTL (time-to-live), then listening for an ICMP "time exceeded" reply from a gateway. host is the destination hostname or the IP number of the host to reach. packetsize is the packet size in bytes of the probe datagram. Default is 40 bytes.

Options

-d: Turn on socket-level debugging.
-g addr: Enable the IP LSRR (Loose Source Record Route) option in addition to the TTL tests, to ask how someone at IP address addr can reach a particular target.
-i interface: Specify the network interface for getting the source IP address for outgoing probe packets. Useful with a multi-homed host. Also see the -s option.
-I: Use ICMP ECHO requests instead of UDP datagrams.
-m max_ttl: Set maximum time-to-live used in outgoing probe packets to max-ttl hops. Default is 30.
-n: Show numerical addresses; do not look up hostnames. (Useful if DNS is not functioning properly.)
-p port: Set base UDP port number used for probe packets to port. Default is (decimal) 33434.
-q n: Set number of probe packets for each time-to-live setting to the value n. Default is 3.
-r: Bypass normal routing tables and send directly to a host on an attached network.
-s src_addr: Use src_addr as the IP address that will serve as the source address in outgoing probe packets.
-t tos: Set the type-of-service in probe packets to tos (default 0). The value must be a decimal integer in the range 0 to 255.
-v: Verbose; received ICMP packets (other than TIME_EXCEEDED and PORT_UNREACHABLE) will be listed.
-w wait: Set time to wait for a response to an outgoing probe packet to wait seconds (default is 5).
-x: Toggle IP checksums, usually to turn them off. IP checksums are always calculated if -I is specified.
-z msecs: Set the delay between probes, in milliseconds. The default is 0.

troff

troff

See groff.

true

true

A null command that returns a successful (0) exit status. See also false.

tset

tset [options] [terminal]
reset [options] [terminal]

Initialize a terminal. The terminal to be initialized is whichever is found first from the value of terminal, the value of the TERM environment variable, or the default terminal type. See also the reset command.

Options

-echar

Set the erase character to char.

-ichar

Set the interrupt character to char.

-I

Do not send terminal or tab initialization strings to the terminal.

-kchar

Set line kill character to char.

-m arg

Specify a mapping from a port type to a terminal, where arg looks like this:

[port type][operator][baud rate][:]terminal type

operator can be any combination of < (less than), > (greater than), @ (equal), and ! (not). The terminal type is a string (e.g., vt100 or xterm).

-q

Print the terminal type on standard output but do not initialize the terminal.

-Q

Don't display values for the erase, interrupt, and line kill characters.

-r

Print the terminal type to standard error.

-s

Print the shell commands that initialize the TERM environment variable on standard output.

-V

Print the version of ncurses used for this program and exit.

tty

tty [options]

Print the filename of the terminal connected to standard input.

Options

--help: Print help message and exit.
-s, --silent, --quiet: Print nothing to standard output, but return an exit status.
--version: Display version information and exit.

tune2fs

tune2fs [options] device

System administration command. Tune the parameters of a Linux Second Extended Filesystem by adjusting various parameters. You must specify the device on which the filesystem resides; it must not be mounted read/write when you change its parameters.

Options

-c max-mount-counts

Specify the maximum number of mount counts between two checks on the filesystem.

-C mount-count

Specify the mount count. For use with -c to force a check the next time the system boots.

-e behavior

Specify the kernel's behavior when encountering errors. behavior must be one of:

continue: Continue as usual.
remount-ro: Remount the offending filesystem in read-only mode.
panic: Cause a kernel panic.

-f

Force completion even if there are errors.

-g group

Allow group (a group ID or name) to use reserved blocks.

-i interval[d|w|m]

Specify the maximum interval between filesystem checks. Units may be in days (d), weeks (w), or months (m). If interval is 0, checking will not be time-dependent.

-j

Add an ext3 journal to the filesystem. If specified without -J, use the default journal parameters.

-J jrnl-options

Specify ext3 journal parameters as a comma-separated list of option=value pairs. The specified options override the default values. Only one size or device option can be specified for a filesystem. Possible options are:

device=ext-jrnl

Attach to the journal block device on ext-jrnl, which must exist and must have the same blocksize as the filesystem to be journaled. ext-jrnl can be specified by its device name, by the volume label (LABEL=label), or by the Universal Unique Identifier (UUID) stored in the journal's ext2 superblock (UUID=uuid; see uuidgen). Create the external journal with:

     mke2fs -O jrnl-dev ext-jrnl

size=jrnl-size

The size of the journal in megabytes. The size must be at least equivalent to 1024 blocks and not more than 102,400 blocks.

-l

Display a list of the superblock's contents.

-L label

Specify the volume label of filesystem. The label must be no more than 16 characters.

-m percentage

Specify the percentage of blocks that will be reserved for use by privileged users.

-M dir

Specify the filesystem's last-mounted directory.

-O option

Set or clear the specified filesystem options in the filesystem's superblock. Specify multiple options as a comma-separated list. Prefixing an option with a caret (^) clears the option. No prefix or a plus sign (+) causes the option to be set. Run e2fsck after changing filetype or sparse_super. The following options can be cleared or set:

filetype: Save file type information in directory entries.
has_journal: Create an ext3 journal. Same as the -j option.
sparse_super: Save space on large filesystems by limiting the number of backup superblocks. Same as -s.

-r num

Specify the number of blocks that will be reserved for use by privileged users.

-s [0|1]

Turn the sparse superblock feature on or off. Run e2fsck after changing this feature.

-T time

Set the time e2fsck was last run. The time specification is international date format, with the time optional; i.e., YYYYMMDD[[HHMM]SS]. If time is specified as time-last-checked, the current time is used.

-u user

Allow user (a user ID or name) to use reserved blocks.

-U uuid

Set the UUID of the filesystem to a UUID generated by uuidgen or to one of the following:

clear: Clear the existing UUID.
random: Randomly generate a new UUID.
time: Generate a new time-based UUID.

tunelp

tunelp device [options]

System administration command. Control a line printer's device parameters. Without options, print information about device(s).

Options

-a [on|off]: Specify whether or not to abort if the printer encounters an error. By default, do not abort.
-c n: Retry device n times if it refuses a character. (Default is 250.) After exhausting n, sleep before retrying.
-i irq: Use irq for specified parallel port. Ignore -t and -c. If 0, restore noninterrupt driven (polling) action.
-o [on|off]: Specify whether to abort if device is not online or is out of paper.
-q [on|off]: Specify whether to print current IRQ setting.
-r: Reset port.
-s: Display printer's current status.
-t time: Specify a delay of time in jiffies to sleep before resending a refused character to the device. A jiffy is defined as either one tick of the system clock or one AC cycle time; it should be approximately 1/100 of a second.
-w time: Specify a delay of time in jiffies to sleep before resending a strobe signal.
-C [on|off]: Specify whether to be extremely careful in checking for printer error. Obsolete; the default beginning with Linux 2.1.131.
-T [on|off]: Tell the lp driver whether it can trust the IRQ. Useful only if using with interrupts, to handle IRQ printing efficiently. Requires at least Linux 2.1.131.

ul [options] [names]

Translate underscores to underlining. The process will vary by terminal type. Some terminals are unable to handle underlining.

Options

-i: When on a separate line, translate - to underline instead of translating underscores.
-t terminal-type: Specify terminal type. By default, TERM is consulted.

umount

umount [options] [directory|special-device]

System administration command. Unmount a filesystem. umount announces to the system that the removable file structure previously mounted on the specified directory is to be removed. umount also accepts the special-device to indicate the filesystem to be unmounted; however, this usage is obsolete and will fail if the device is mounted on more than one directory. Any pending I/O for the filesystem is completed, and the file structure is flagged as clean. A busy filesystem cannot be unmounted.

Options

-a: Unmount all filesystems that are listed in /etc/mtab.
-d: If the unmounted device was a loop device, free the loop device too. See also the losetup command.
-f: Force the unmount. This option requires kernel 2.1.116 or later.
-h: Print help message and exit.
-l: Lazy unmount. Detach the filesystem from the hierarchy immediately, but don't clean up references until it is no longer busy. Requires kernel 2.4.11 or later.
-n: Unmount, but do not record changes in /etc/mtab.
-O options: Unmount only filesystems with the specified options in /etc/fstab. Specify multiple options as a comma-separated list. Add no as a prefix to an option to indicate filesystems that should not be unmounted.
-r: If unmounting fails, try to remount read-only.
-t type: Unmount only filesystems of type type. Multiple types can be specified as a comma-separated list, and any type can be prefixed with no to specify that filesystems of that type should not be unmounted.
-v: Verbose mode.
-V: Print version information and exit.

uname

uname [options]

Print information about the machine and operating system. Without options, print the name of the operating system (Linux).

Options

-a, --all: Combine all the system information from the other options.
-i, --hardware-platform: Print the system's hardware platform.
-m, --machine: Print the name of the hardware the system is running on.
-n, --nodename: Print the machine's hostname.
-o, --operating-system: Print the operating system name.
-p, --processor: Print the type of processor (not available on all versions).
-r, --kernel-release: Print the release number of the kernel.
-s, --kernel-name: Print the name of the kernel (Linux). This is the default action.
-v, --kernel-version: Print build information about the kernel.
--help: Display a help message and then exit.
--version: Print version information and then exit.

uncompress

uncompress [options] files

Uncompress files that were compressed (i.e., whose names end in .Z). uncompress takes all the same options as compress except -r and -b.

unexpand

unexpand [options] [files]

Convert strings of initial whitespace, consisting of at least two spaces and/or tabs, to tabs. Read from standard input if given no file or a file named -.

Options

-a, --all: Convert all, not just initial, strings of spaces and tabs.
-nums, -t nums, --tabs nums: nums is a comma-separated list of integers that specify the placement of tab stops. If a single integer is provided, the tab stops are set to every integer spaces. By default, tab stops are eight spaces apart. With -t and --tabs, the list may be separated by whitespace instead of commas. This option implies -a.
--help: Print help message and then exit.
--version: Print the version number and then exit.

unicode_start

unicode_start [font [umap]]

Put keyboard and console in Unicode mode, setting the font to font and the Unicode map to umap if the font doesn't have its own map. If no font is specified, use the default.

unicode_stop

unicode_stop

Take keyboard and console out of Unicode mode.

uniq

uniq [options] [file1 [file2]]

Remove duplicate adjacent lines from sorted file1, sending one copy of each line to file2 (or to standard output). Often used as a filter. Specify only one of -d or -u. See also comm and sort.

Options

-n, -f n, --skip-fields=n: Ignore first n fields of a line. Fields are separated by spaces or by tabs.
+n, -s n, --skip-chars=n: Ignore first n characters of a field.
-c, --count: Print each line once, prefixing number of instances.
-d, --repeated: Print duplicate lines once but no unique lines.
-D, --all-repeated[=method]: Print all duplicate lines. -D takes no delimiter method. The delimiter method method takes one of the values none (default), prepend, or separate. Blank lines are used as the delimiter.
-i, --ignore-case: Ignore case differences when checking for duplicates.
-u, --unique: Print only unique lines (no copy of duplicate entries is kept).
-w n, --check-chars=n: Compare only first n characters per line (beginning after skipped fields and characters).
--help: Print a help message and then exit.
--version: Print version information and then exit.

Examples

Send one copy of each line from list to output file list.new:

uniq list list.new

Show which names appear more than once:

sort names | uniq -d

unshar

unshar [options] [files]

Unpack a shell archive (shar file). unshar scans mail messages looking for the start of a shell archive. It then passes the archive through a copy of the shell to unpack it. unshar accepts multiple files. If no files are given, standard input is used.

Options

-c, --overwrite: Overwrite existing files.
-d directory, --directory=directory: Change to directory before unpacking any files.
-e, --exit-0: Sequentially unpack multiple archives stored in same file. This uses the clue that many shar files are terminated by an exit 0 at the beginning of a line. (Equivalent to -E "exit 0".)
-E string, --split-at=string: Like -e, but allows you to specify the string that separates archives.
-f, --force: Same as -c.
--help: Print help message and then exit.
--version: Print the version number and then exit.

update

update [options]

System administration command. update is a daemon that controls how often the kernel's disk buffers are flushed to disk. update is also known as bdflush. The daemon forks a couple of processes to call system functions flush( ) and sync( ). When called by an unprivileged user, no daemon is created. Instead, update calls sync( ) and then exits. By default, update will wake up every 5 seconds and flush( ) some dirty buffers. If that doesn't work, it will try waking up every 30 seconds to sync( ) the buffers to disk. Not all of the listed options are available in every version of update.

Options

-d: Display the kernel parameters. This does not start the update daemon.
-f seconds: Call flush( ) at this interval. Default is 5.
-h: Help. Print a command summary.
-s seconds: Call sync( ) at this interval. Default is 30.
-0 percent: Flush buffers when the specified percent of the buffer cache is dirty.
-1 blocks: The maximum number of dirty blocks to write out per wake cycle.
-2 buffers: The number of clean buffers to try to obtain each time the free buffers are refilled.
-3 blocks: Flush buffers if dirty blocks exceed blocks when trying to refill the buffers.
-4 percent: Percent of buffer cache to scan when looking for free clusters.
-5 seconds: Time for a data buffer to age before being flushed.
-6 seconds: Time for a nondata buffer to age before being flushed.
-7 constant: The time constant to use for load average.
-8 ratio: How low the load average can be before trimming back the number of buffers.

uptime

uptime [option]

Print the current time, how long the system has been running, the number of users currently logged in (which may include the same user multiple times), and system load averages. This output is also produced by the first line of the w command.

Option

-V: Print version information and exit.

useradd

useradd [options] [user]

System administration command. Create new user accounts or update default account information. Unless invoked with the -D option, user must be given. useradd will create new entries in system files. Home directories and initial files may also be created as needed.

Options

-c comment

Comment field.

-d dir

Home directory. The default is to use user as the directory name under the home directory specified with the -D option.

-e date

Account expiration date. date is in the format MM/DD/YYYY. Two-digit year fields are also accepted. The value is stored as the number of days since January 1, 1970. This option requires the use of shadow passwords.

-f days

Permanently disable account this many days after the password has expired. A value of -1 disables this feature. This option requires the use of shadow passwords.

-g group

Initial group name or ID number. If a different default group has not been specified using the -D option, the default group is 1.

-G groups

Supplementary groups given by name or number in a comma-separated list with no whitespace.

-k [dir]

Copy default files to the user's home directory. Meaningful only when used with the -m option. Default files are copied from /etc/skel/ unless an alternate dir is specified.

-m

Make user's home directory if it does not exist. The default is not to make the home directory.

-M

Do not create a home directory for the user, even if the system default in /etc/login.defs is to create one.

-n

Red Hat-specific option. Turn off the Red Hat default that creates a group with the same name as the username and puts the user in that group.

-o

Override. Accept a nonunique uid with the -u option. (Probably a bad idea.)

-p passwd

The encrypted password, as returned by crypt(3).

-r

Red Hat-specific option. Create a system account with a non-expiring password and a UID lower than the minimum defined in /etc/login.defs. Do not create a home directory for the account unless -m is also specified.

-s shell

-u uid

Numerical user ID. The value must be unique unless the -o option is used. The default value is the smallest ID value greater than 99 and greater than every other uid.

-D [options]

Set or display defaults. If options are specified, set them. If no options are specified, display current defaults. The options are:

-b dir: Home directory prefix to be used in creating home directories. If the -d option is not used when creating an account, the user name will be appended to dir.
-e date: Expire date. Requires the use of shadow passwords.
-f days: Number of days after a password expires to disable an account. Requires the use of shadow passwords.
-g group: Initial group name or ID number.
-s shell: Default login shell.

userdel

userdel [option] user

System administration command. Delete all entries for user in system account files.

Option

-r: Remove the home directory of user and any files contained in it.

usermod

usermod [options] user

System administration command. Modify user account information.

Options

-c comment: Comment field.
-d dir: Home directory.
-e date: Account expiration date. date is in the format MM/DD/YYYY; two-digit year fields are also accepted. The value is stored as the number of days since January 1, 1970. This option requires the use of shadow passwords.
-f days: Permanently disable account this many days after the password has expired. A value of -1 disables this feature. This option requires the use of shadow passwords.
-g group: Initial group name or number.
-G groups: Supplementary groups given by name or number in a comma-separated list with no whitespace. user will be removed from any groups to which it currently belongs that are not included in groups.
-l name: Login name. This cannot be changed while the user is logged in.
-L: Lock user's password by putting a ! in front of it. This option cannot be used with -p or -U.
-o: Override. Accept a nonunique uid with the -u option.
-p pw: Encrypted password, as returned from crypt(3).
-s shell: Login shell.
-u uid: Numerical user ID. The value must be unique unless the -o option is used. Any files owned by user in the user's home directory will have their user ID changed automatically. Files outside of the home directory will not be changed. user should not be executing any processes while this is changed.
-U: Unlock the user's password by removing the ! that -L put in front of it. This option cannot be used with -p or -L.

users

users [file]users option

Print a space-separated list of each login session on the host. Note that this may include the same user multiple times. Consult file or, by default, /var/log/utmp or /var/log/wtmp.

Options

--help: Print usage information and exit.
--version: Print version information and exit.

usleep

usleep [microseconds]usleep [options]

Sleep some number of microseconds (default is 1).

Options

-?, --help: Print help information and then exit.
--usage: Print usage message and then exit.
-v, --version: Print version information.

uudecode

uudecode [-o outfile] [file]

Read a uuencoded file and re-create the original file with the permissions and name set in the file (see uuencode). The -o option specifies an alternate output file.

uuencode

uuencode [-m] [file] name

Encode a binary file. The encoding uses only printable ASCII characters and includes the permissions and name of the file. When file is reconverted via uudecode, the output is saved as name. If the file argument is omitted, uuencode can take standard input, so a single argument is taken as the name to be given to the file when it is decoded. With the -m option, base64 encoding is used.

Examples

It's common to encode a file and save it with an identifying extension, such as .uue. This example encodes the binary file flower12.jpg, names it rose.jpg, and saves it to a .uue file:

% uuencode flower12.jpg rose.jpg > rose.uue

Encode flower12.jpg and mail it:

% uuencode flower12.jpg flower12.jpg | mail el@oreilly.com

uuidgen

uuidgen [option]

Create a new Universal Unique Identifier (UUID) and print it to standard output. The generated UUID consists of five hyphen-separated groups of hex digits (e.g., 3cdfc61d-87d3-41b5-ba50-32870b33dc67). The default is to generate a random-based UUID, but this requires that a high-quality random-number generator be available on the system.

Options

-r: Generate a random-based UUID.
-t: Generate a time-based UUID.

vacation

vacationvacation [options] [user]

Automatically return a mail message to the sender announcing that you are on vacation.

Use vacation with no options to initialize the vacation mechanism. The process performs several steps.

Creates a .forward file in your home directory. The .forward file contains:
```
\user, "|/usr/bin/vacation user"
```
user is your login name. The action of this file is to actually deliver the mail to user (i.e., you) and to run the incoming mail through vacation.
Creates the .vacation.pag and .vacation.dir files. These files keep track of who has sent you messages so that they receive only one "I'm on vacation" message from you per week.
Starts an editor to edit the contents of .vacation.msg. The contents of this file are mailed back to whomever sends you mail. Within its body, $subject is replaced with the contents of the incoming message's Subject line.

Remove or rename the .forward file to disable vacation processing.

Options

The -a and -r options are used within a .forward file; see the example.

-a alias: Mail addressed to alias is actually mail for the user and should produce an automatic reply.
-i: Reinitialize the .vacation.pag and .vacation.dir files. Use this right before leaving for your next vacation.
-r interval: By default, no more than one message per week is sent to any sender; this option changes that interval. interval is a number with a trailing s, m, h, d, or w indicating seconds, minutes, hours, days, or weeks, respectively. If interval is infinite, only one reply is sent to each sender.

Example

Send no more than one reply every three weeks to any given sender:

$ cd
$ vacation -I
$ cat .forward
\jp, "|/usr/bin/vacation -r3w jp"
$ cat .vacation.msg
From: jp@wizard-corp.com (J. Programmer, via the vacation program)
Subject: I'm out of the office ...

Hi. I'm off on a well-deserved vacation after finishing
up whizprog 1.0. I will read and reply to your mail
regarding "$SUBJECT" when I return.

Have a nice day.

vdir

vdir [options] [files]

Verbosely list directory contents. Equivalent to ls -lb. By default, list the current directory. Directory entries are sorted alphabetically unless overridden by an option. vdir takes the same options as ls.

vi [options] [files]

A screen-oriented text editor based on ex. For more information on vi, see Chapter 11.

vidmode

vidmode [option] image [mode [offset]]

System administration command. Set the video mode for a kernel image. If no arguments are specified, print current mode value. mode is a 1-byte value located at offset 506 in a kernel image. You may change the mode by specifying the kernel image to change, the new mode, and the byte offset at which to place the new information (the default is 506). Note that rdev -v is a synonym for vidmode. If LILO is used, vidmode is not needed. The video mode can be set from the LILO prompt during a boot.

Modes

-3: Prompt
-2: Extended VGA
-1: Normal VGA
0: Same as entering 0 at the prompt
1: Same as entering 1 at the prompt
2: Same as entering 2 at the prompt
3: Same as entering 3 at the prompt
n: Same as entering n at the prompt

Option

-o offset: Same as specifying an offset as an argument.

vim

vim

An enhanced version of the vi screen editor. Both vi and vim are covered in Chapter 11.

vmstat

vmstat [options] [interval [count]]

Print report on virtual memory statistics, including information on processes, memory, swap space, I/O, system and CPU usage. vmstat will first report average values since the last system reboot. If given a sampling period interval in seconds, it will print additional statistics for each interval. If specified, vmstat will exit when it has completed count reports. Otherwise, it will continue until it receives a Ctrl-C, printing a new header line each time it fills the screen.

Options

-n: Don't print new header lines when the screen is full.
-V: Print version number, then exit.

Fields

procs

r: Processes waiting for run time.
b: Uninterruptable sleeping processes.
w: Swapped but runnable processes.

memory

swpd: Virtual memory used, in kilobytes.
free: Idle memory, in kilobytes.
buff: Memory used as buffers, in kilobytes.

swap

si: Memory swapped in from disk each second, in kilobytes.
so: Memory swapped out to disk each second, in kilobytes.

io

bi: Blocks sent to block devices each second.
bo: Blocks received from block devices each second.

system

in: Interrupts per second, including clock interrupts.
cs: Context switches per second.

cpu

us: Percentage of CPU time consumed by user processes.
sy: Percentage of CPU time consumed by system processes.
id: Percentage of CPU time spent idle.

volname

volname [devfile]

Return the volume name for a device such as a CD-ROM that was formatted with an ISO-9660 filesystem. The default device file devfile is /dev/cdrom.

w [options] [user]

Print summaries of system usage, currently logged-in users, and what those users are doing. w is essentially a combination of uptime, who, and ps -a. Display output for one user by specifying user.

Options

-f: Toggle printing the from (remote hostname) field.
-h: Suppress headings and uptime information.
-s: Use the short format.
-u: Ignore the username while figuring out the current process and CPU times.
-V: Display version information.

File

/var/run/utmp: List of users currently logged in.

wall

wall [file]
wall [message]

Write to all users. Depending on your Linux distribution, wall uses one of the two syntaxes shown. In both versions, the default is for wall to read a message from standard input and send the message to all users currently logged in, preceded by "Broadcast Message from...". With the first syntax, which comes with Debian for example, if file is specified, wall reads input from that file rather than from standard input, and only the superuser can write to a terminal if the user has disallowed messages. With the second syntax, distributed by Red Hat for example, the text of the message can be included on the command line, and the message is limited to 20 lines.

watch

watch [options] command [cmd_options]

Run the specified command repeatedly (by default, every 2 seconds) and display the output so you can watch it change over time. The command and any options are passed to sh -c, so you may need to use quotes to get correct results.

Options

-d, --differences[=cumulative]: Highlight changes between iterations. If cumulative is specified, the highlighting remains on the screen throughout, giving a cumulative picture of the changes.
-h, --help: Display help message and exit.
-n secs, --interval=secs: Run the command every secs seconds.
-v, --version: Print version information and exit.

wc [options] [files]

Print byte, word, and line counts for each file. Print a total line for multiple files. If no files are given, read standard input. See other examples under ls and sort.

Options

-c, --bytes: Print byte count only.
-l, --lines: Print line count only.
-L, --max-line-length: Print length of longest line.
-m, --chars: Print character count only.
-w, --words: Print word count only.
--help: Print help message and then exit.
--version: Print the version number and then exit.

Examples

Count the number of users logged in:

who | wc -l

Count the words in three essay files:

wc -w essay.[123]

Count lines in the file named by variable $file (don't display filename):

wc -l < $file

whatis

whatis keywords

Search the short manual page descriptions in the whatis database for each keyword and print a one-line description to standard output for each match. Like apropos, except that it searches only for complete words. Equivalent to man -f.

whereis

whereis [options] files

Locate the binary, source, and manual page files for specified commands/files. The supplied filenames are first stripped of leading pathname components and any (single) trailing extension of the form .ext (for example, .c). Prefixes of s. resulting from use of source code control are also dealt with. whereis then attempts to locate the desired program in a list of standard Linux directories (/bin, /etc, /usr/bin, /usr/local/bin/, etc.).

Options

-b: Search only for binaries.
-f: Terminate the last directory list and signal the start of filenames. Required when the -B, -M, or -S option is used.
-m: Search only for manual sections.
-s: Search only for sources.
-u: Search for unusual entries, that is, files that do not have one entry of each requested type. Thus, the command whereis -m -u * asks for those files in the current directory that have no documentation.
-B directories: Change or otherwise limit the directories to search for binaries.
-M directory: Change or otherwise limit the directories to search for manual sections.
-S directory: Change or otherwise limit the directories to search for sources.

Example

Find all files in /usr/bin that are not documented in /usr/share/man/man1 but that have source in /usr/src:

% cd /usr/bin
% whereis -u -M /usr/share/man/man1 -S /usr/src -f *

which

which [options] [--] [commands]

List the full pathnames of the files that would be executed if the named commands had been run. which searches the user's $PATH environment variable. tcsh has a built-in which command that has no options. To use the options with tcsh, specify the full pathname (e.g., /usr/bin/which).

Options

-a, --all: Print all matches, not just the first.
-i, --read-alias: Read aliases from standard input and write matches to standard output. Useful for using an alias for which.
--read-functions: Read shell functions from standard input and report matches to standard output. Useful for also using a shell function for which itself.
--skip-alias: Ignore --read-alias if present. Useful for finding normal binaries while using --read-alias in an alias for which.
--skip-dot: Skip directories that start with a dot.
--skip-functions: Ignore --read-functions if present. Useful when searching for normal binaries while using --read-functions in an alias or function for which.
--skip-tilde: Skip directories that start with a tilde (~) and executables in $HOME.
--show-dot: If a matching command is found in a directory that starts with a dot, print ./cmdname instead of the full pathname.
--show-tilde: Print a tilde (~) to indicate the user's home directory. Ignored if the user is root.
--tty-only: Stop processing options on the right if not on a terminal.
-v, -V, --version: Print version information and then exit.
--help: Print help information and then exit.

Example

 which cc ls
/usr/bin/cc
ls:      aliased to ls -sFC

who

who [options] [file]
who am i

Show who is logged into the system. With no options, list the names of users currently logged in, their terminal, the time they have been logged in, and the name of the host from which they have logged in. An optional system file (default is /etc/utmp) can be supplied to give additional information.

Options

am i

Print the username of the invoking user.

--help

Include idle times. An idle time of . indicates activity within the last minute; one of old indicates no activity in more than a day.

-i, -u, --idle

-l, --lookup

Attempt to include canonical hostnames via DNS.

-m

Same as who am i.

-q, --count

"Quick." Display only the usernames and total number of users.

--version