Chapter 3. Linux Commands

System administration command. The Linux version of getty. Set terminal type, modes, speed, and line discipline. agetty is invoked by init. It is the second process in the series init-getty-login-shell, which ultimately connects a user with the Linux system. agetty reads the user's login name and invokes the login command with the user's name as an argument. While reading the name, agetty attempts to adapt the system to the speed and type of device being used.

You must specify a port, which agetty will search for in the /dev directory. You may use -, in which case agetty reads from standard input. You must also specify baudrate, which may be a comma-separated list of rates, through which agetty will step. Optionally, you may specify the term, which is used to override the TERM environment variable.

Options

-h

Specify hardware, not software, flow control.

-i

Suppress printing of /etc/issue before printing the login prompt.

-l program

Specify the use of program instead of /bin/login.

-m

Attempt to guess the appropriate baud rate.

-t timeout

Specify that agetty should exit if the open on the line succeeds and there is no response to the login prompt in timeout seconds.

-L

Do not require carrier detect; operate locally only. Use this when connecting terminals.

Options

-c n, --check n

Set the number of seconds to wait for an event before rechecking the power level. Default is to wait indefinitely. Setting this causes the battery levels to be checked more frequently.

-P command, --apmd_prxy command

Specify the apmd_proxy command to run when APM driver events are reported. This is generally a shell script. The command will be invoked with parameters indicating what kind of event was received. The parameters are in the next list.

-p n, --percentage n

Log information whenever the power changes by n percent. The default is 5. Values greater than 100 will disable logging of power changes.

-V, --version

Print version and exit.

-v, --version

Verbose mode; all events are logged.

-W, --wall

Use wall to alert all users of a low battery status.

-w n, --warn n

Log a warning at ALERT level when the battery charge drops below n percent. The default is 10. Negative values disable low battery level warnings.

-q, --quiet

Disable low battery level warnings.

-?, --help

Print help summary and exit.

Parameters

The apmd proxy script will be invoked with the following parameters:

Search the short manual page descriptions in the whatis database for occurrences of each string and display the result on the standard output. Like whatis, except that it searches for strings instead of words. Equivalent to man -k.

Key

d

Delete files from archive.

m

Move files to end of archive.

p

Print files in archive.

q

Append files to archive.

r

Replace files in archive.

t

List the contents of archive or list the named files.

x

Extract contents from archive or only the named files.

Arguments

a

Use with r or m key to place files in the archive after posname.

b

Same as a but before posname.

c

Create archive silently.

f

Truncate long filenames.

i

Same as b.

l

For backward compatibility; meaningless in Linux.

o

Preserve original timestamps.

s

Force regeneration of archive symbol table (useful after running strip).

S

Do not regenerate symbol table.

u

Use with r to replace only files that have changed since being put in archive.

v

Verbose; print a description of actions taken.

Example

Replace mylib.a with object files from the current directory:

ar r mylib.a `ls *.o

Print machine architecture type to standard output. Equivalent to uname -m.

TCP/IP command. Clear, add to, or dump the kernel's ARP cache (/proc/net/arp).

Options

-v

Verbose mode.

-t type

Search for type entries when examining the ARP cache. type must be ether (Ethernet) or ax25 (AX.25 packet radio); ether is the default.

-a [hosts]

Display hosts' entries or, if none are specified, all entries.

-d host

Remove host's entry.

-s host hardware-address

Add the entry host hardware-address, where ether class addresses are 6 hexadecimal bytes, colon-separated.

-f file

Read entries from file and add them.

Generate an object file from each specified assembly language source file. Object files have the same root name as source files but replace the .s suffix with .o. There may be some additional system-specific options.

Options

-- [ | files]

Read input files from standard input, or from files if the pipe is used.

-a[dhlns][=file]

With only the -a option, list source code, assembler listing, and symbol table. The other options specify additional things to list or omit:

-ad

Omit debugging directives.

-ah

Include the high-level source code, if available.

-al

Include an assembly listing.

-an

Suppress forms processing.

-as

Include a symbol listing.

=file

Set the listing filename to file.

-defsym symbol=value

Define the symbol to have the value value, which must be an integer.

-f

Skip preprocessing.

--gstabs

Generate stabs debugging information.

-o objfile

Place output in object file objfile (default is file.o).

-v

Display the version number of the assembler.

-I path

Include path when searching for .include directives.

-K

Warn before altering difference tables.

-L

Do not remove local symbols, which begin with L.

-R

Combine both data and text in text section.

-W

Quiet mode.

The at command can always be issued by a privileged user. Other users must be listed in the file /etc/at.allow if it exists; otherwise, they must not be listed in /etc/at.deny. If neither file exists, only a privileged user can issue the command.

Options

-c job [job...]

Display the specified jobs on the standard output. This option does not take a time specification.

-d job [job...]

Delete the specified jobs. Same as atrm.

-f file

Read job from file, not standard input.

-l

Report all jobs that are scheduled for the invoking user. Same as atq.

-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 any single letter from a-z or A-Z. Default queue is a. (The batch queue defaults to b.) Higher-lettered queues run at a lower priority.

-V

Display the version number.

Time

hh:mm [modifiers]

Hours can have one digit or two (a 24-hour clock is assumed by default); optional minutes can be given as one or two digits; the colon can be omitted if the format is h, hh, or hhmm; (e.g., valid times are 5, 5:30, 0530, 19:45). If modifier am or pm is added, time is based on a 12-hour clock. If the keyword zulu is added, times correspond to Greenwich Mean Time.

midnight | noon | teatime | now

Use any one of these keywords in place of a numeric time. teatime translates to 4:00 p.m.; now must be followed by an increment.

Date

month num[, year]

month is one of the 12 months, spelled out or abbreviated to its first three letters; num is the calendar date of the month; year is the four-digit year. If the given month occurs before the current month, at schedules that month next year.

day

One of the seven days of the week, spelled out or abbreviated to its first three letters.

today | tomorrow

Indicate the current day or the next day. If date is omitted, at schedules today when the specified time occurs later than the current time; otherwise, at schedules tomorrow.

Increment

Supply a numeric increment if you want to specify an execution time or day relative to the current time. The number should precede any of the keywords minute, hour, day, week, month, or year (or their plural forms). The keyword next can be used as a synonym of + 1.

Examples

Note that the first two commands are equivalent:

at 1945 pm December 9
at 7:45pm Dec 9
at 3 am Saturday
at now + 5 hours
at noon next day

Options

-q queue

Query only the specified queue and ignore all other queues.

-v

Show jobs that have completed but not yet been deleted.

-V

Print the version number.

Delete jobs that have been queued for future execution. Same as at -d.

Options

-q queue

Remove job from the specified queue.

-V

Print the version number and then exit.

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.

-o file

Direct output to file.

-v

Verbose mode.

-w

Test by writing to each block and then reading back from it.

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

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

Execute commands entered on standard input. If time is omitted, execute them 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 a. (The batch queue defaults to b.) 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.

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

-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 = 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}

Similar to while; for example, to print the first 10 multiples of 5, you could type:

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

GNU bf 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.

Function keywords

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

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

Given a file containing context-free grammar, convert into tables for subsequent parsing while sending output to file.c. This utility is both to a large extent compatible with yacc and 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.

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 command-line specified dumpfile.

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 next.

Tags

Internet Boot Protocol Gateway. Maintain a gateway that forwards bootpd requests to server. In addition to dealing with BOOTREPLY packets, also deal with BOOTREQUEST packets. bootpgw is normally run by /etc/inetd by including the following line in the file /etc/inetd.conf:

bootps dgram udp wait root /etc/bootpgw bootpgw

This causes bootpgw to be started only when a boot request arrives. bootpgw takes all the same options as bootpd, except -c.

TCP/IP command. Test server's bootpd daemon by sending requests every second for 10 seconds or until the server responds. Read options from the template file, if provided.

Options

-f file

Read the boot filename from file.

-h

Identify client by hardware, not IP, address.

-m magic-number

Provide magic-number as the first word of the vendor options field.

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

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. Show the compression ratio for each file processed. Add more -v's to increase the verbosity.

-z, --compress

Forces 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.

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

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.

Options

Read (concatenates) 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

Options

-$

Do not allow $ in identifiers.

-dM

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

-dD

Similar to -dM but exclude predefined macros and include results of preprocessing.

-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.

-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.

-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.

-pedantic

Warn verbosely.

-pedantic-errors

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

-traditional

Behave like traditional C, not ANSI.

-undef

Suppress definition of all nonstandard macros.

-Aname[=def]

Assert name with value def as if defined by a #assert.

-C

Pass along 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.

-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.

-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.

-MD file

Similar to -M, but output to file; also compile the source.

-MM

Similar to -M. Describe only those files included as a result of #include "file".

-MMD file

Similar to -MD, but describe only the user's header files.

-P

Preprocess input without producing line-control information used by next pass of 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).

-Wcomment, -Wcomments

Warn when encountering the beginning of a nested comment.

-Wtraditional

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

Special names

cpp understands various special names, some of which are:

__DATE__

Current date (e.g., Oct 10 1999)

__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 macros, just like any other defined names. cpp's understanding of the line number and filename may be changed using a #line directive.

Directives

System administration command. Partition a hard disk. device may be /dev/hda (default), /dev/hdb, /dev/sda, /dev/sdb, /dev/sdc, or /dev/sdd. See also fdisk.

Options

-a

Highlight the current partition with a cursor, not reverse video.

-c cylinders

Specify the number of cylinders.

-h heads

Specify the number of heads.

-s sectors

Specify the number of sectors per track.

-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. Note that this letter must be uppercase.

Modify file attributes. Specific to Linux Second Extended Filesystem. 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.

s

Secure deletion; the contents are zeroed on deletion.

u

Undeletable.

S

Synchronous updates.

Examples

chattr +a myfile     As superuser

Change the information that is stored in /etc/passwd and displayed when a user is fingered. 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, --help

Print help message and then exit.

-v, --version

Print version information and then exit.

Example

chfn -f "Ellen Siever" ellen

Options

-c, --changes

Print information about those 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.

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 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; save text (file) mode or prevent removal of files by nonowners (directory).

u

User's present permission.

g

Group's present permission.

o

Other's present permission.

4

Read.

2

Write.

1

Execute.

Note: 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 file's owner, not on permissions of 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 user who created the process.

1

Set sticky bit.

Examples

Add execute-by-user permission to file:

chmod u+x 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

Set the user ID, assign read/write/execute permission by owner, and assign read/execute permission by group and others:

chmod 4755 file

Options

-c, --changes

Print information about those 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.

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 will be encrypted before being stored.

Option

-e

Passwords given are already encrypted.

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.

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

Compute a cyclic redundancy check (CRC) checksum for all files; 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.

Compare file1 with file2. Use standard input if file1 is - or missing. See also comm and diff. Files can be of any type. 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'

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

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.

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

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.

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; that is, 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

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.

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. 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 (e.g., 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.

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 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 filenames from the archives 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; for copy-in the default 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. Useful 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 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

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

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

Indicates which user's crontab file will be acted upon.

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 exactly 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}

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

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.

-rregexp, --regex=regexp

Include a tag for each line that matches regexp in the files following this option.

-R, --no-regex

Don't include tags based on regular-expression matching for the files that follow this option.

-t, --typedefs

Include tag entries for typedefs.

-u, --update

Update tags file to reflect new locations of functions (e.g., when functions are moved to a different source file). Old tags are deleted; new tags are appended.

-v, --vgrind

Print to standard output a listing (index) of each function, source file, and page number (1 page = 64 lines).

-w, --no-warn

Suppress warning messages.

-x, --cxref

Produce a listing of each function, and its line number, source file, and context.

-B, --backward-search

Search for tags backward through files.

-C, --c++

Expect .c and .h files to contain C++, not C, code.

-H, -h, --help

Print usage information and exit.

-S, --ignore-indentation

Normally ctags uses indentation to parse the tag file; this option tells it to rely on it 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 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 then exit.

--version

Print version information and then 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

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 "Format" section that follows).

-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

%

Literal %.

-

Do not pad fields (default: pad fields with zeros).

_

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," 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.

%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.

%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

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.

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; write it as fixed-length to out:

data_retrieval_cmd | dd of=out conv=sync,block

System administration command. Debug an ext2 filesystem. device is the special file corresponding to the device containing the ext2 filesystem (e.g., /dev/hda3).

Option

-w

Open the filesystem read-write.

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.

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.

ln source_file dest_file

Create a link.

ls [pathname]

Emulate the ls command.

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 [-w] device

Open a filesystem.

pwd

Print the current working directory.

quit

Quit debugfs.

rm file

Remove file.

rmdir directory

Remove directory.

setb block

Mark block as allocated.

seti file

Mark in use the inode corresponding to file.

show_super_stats

List the contents of the super block.

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

Create a file in the filesystem named file, and copy the contents of source_file into the destination file.

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 the correct module dependencies will be available after booting the system.

Options

-a

Create dependencies for all modules listed in /etc/conf.modules.

-d

Debug mode. Show all commands being issued.

-e

Print a list of all unresolved symbols.

-v

Print a list of all processed modules.

Files

/etc/conf.modules

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.

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.

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.

-Dsymbol, --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

For context and unified diff, print n lines of context. Same as specifying a number with -C or -U.

Compare 3 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 are places where both of the newer files differ from each other and at least one of them 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

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 is 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 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]

Wait timeout seconds for text to arrive from the remote system. If timeout is not specified, wait forever.

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.

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.

-n level

Set the level of system message that will display on console.

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

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.

Options

-a

Automatically repair the system; do not prompt the user.

-A

Use the Atari version of the MS-DOS filesystem.

-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.

-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.

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

Options

-a, --all

Print 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-reader-friendly 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.

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

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

System administration command. Similar to fsck, but specifically intended for Linux Second Extended Filesystems. When checking a second extended filesystem, fsck calls this command.

Options

-b superblock

Use superblock instead of 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.

\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"

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.

Create a list of function and macro names that are defined in the specified C, Pascal, FORTRAN, yacc, or flex source files. 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 Emacs on any file and type:

ESC-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:

ESC-x find-tag

You will be prompted for the tag you would like Emacs to search for. ctags produces an equivalent tags file for use with vi.

Options

Options

-tabs, -t, --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.

Evaluate arguments as expressions and print the result. 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

+

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

|

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 \( \), 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.)

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

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.

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 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

-l

List partition tables and exit.

-spartition

Display the size of partition, unless it is a DOS partition.

Commands

a

Toggle a bootable flag on current partition.

d

Delete current partition.

l

List all partition types.

m

Main menu.

n

Create a new partition; prompt for more information.

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; display a summary of the number of unallocated sectors.

w

Save changes; exit.

Options