The following list describes some of the most useful and popular Linux commands. Consult the manpage for each command to learn about additional arguments and details of operation.
userid
Creates a new
userid
, prompting for necessary information
(requires root privileges).
command
'keyword
Searches the manual pages for occurrences of the specified keyword and prints short descriptions from the beginning of matching manual pages.
time
,
at -f
file time
Executes commands entered via STDIN
(or by using the alternative form, the specified file) at the
specified time. The time can be specified in a variety of ways; for
example, in hour and minute format (hh:mm)
or in
hour, minute, month, day, and year format (hh:mm
mm/dd/yy)
.
job
Cancels execution of a job scheduled via the at command. Use the atq command to discover the identities of scheduled jobs.
jobs
Places the current job
(or by using the alternative form, the specified jobs) in the
background, suspending its execution so that a new user prompt
appears immediately. Use the jobs
command to discover the identities of background jobs.
month year
Displays a calendar for the specified month of the specified year.
files
directory
Changes the current working directory to the user’s home directory or the specified directory.
group files
,
chgrp -R
group files
Changes
the group
of the specified files
to the specified group. The alternative form of the
command operates recursively, changing the group of subdirectories
and files beneath a specified directory. The group must be named in
the /etc/groups
file, maintained by the
newgroup command.
mode files
,
chmod -R
mode files
Changes the access mode of the specified files to the specified mode. The alternative form of the command operates recursively, changing the mode of subdirectories and files beneath a specified directory.
userid files
,
chown -R
userid files
Changes
the owner of the specified files to the specified
userid
. The alternative form of the command
operates recursively, changing the owner of subdirectories and files
beneath a specified directory
file1 file2
Compares two
files, reporting all discrepancies. Unlike the diff command, cmp
can compare multiple files
and binary
files.
file1 file2
,
cp
files directory
,
cp -R
files directory
Copies a file
to
another file
or directory or copies a
subdirectory and all its files to another directory.
date
Displays
the current date and time or changes the system date and time to the
specified value, of the form MMddhhmmyy
or
MMddhhmmyyyy
.
Displays the amount of free disk space on each mounted filesystem.
file1 file2
Compares two files, reporting all discrepancies. Similar to the cmp command, though the output format differs.
Displays the messages resulting from the most recent system boot.
directories
Displays the amount of disk space used by the current directory (or the specified directories) and its (their) subdirectories.
string
,
echo -n
string
Displays the specified text on the standard output stream. The -n option causes omission of the trailing newline character.
device
Formats the media inserted in the specified floppy disk drive. The command performs a low-level format only; it does not create a filesystem. To create a filesystem, issue the mkfs command after formatting the media.
device
jobs
Brings the current job
(or the specified jobs
) to the foreground.
files
Determines and prints a description of the type of each specified file.
path -
name
pattern -
print
Searches the
specified path
for files with names matching the
specified pattern
(usually enclosed in single
quotes) and prints their names. The find command has many other arguments and
functions; see the online documentation.
users
hostname
Opens an FTP connection to the specified host, allowing files to be transferred. The FTP program provides subcommands for accomplishing file transfers; see the online documentation.
pattern files
,
grep -i
pattern files
,
grep -n
pattern files
,
grep -v
pattern files
Searches the specified
files
for text matching the specified
pattern
(usually enclosed in single quotes) and
prints matching lines. The -i option
specifies that matching is performed without regard to case. The
-n option specifies that each line
of output is preceded by the filename and line number. The -v option reverses the matching, causing
nonmatched lines to be printed.
files
,
gunzip
files
Expands or compresses the specified
files
. Generally, a compressed file has the same
name as the original file, followed by .gz
.
files
name
runlevel
Changes the system runlevel to the
specified value (requires root
privileges).
module
Dynamically
loads the specified module
(requires
root
privileges).
files
process_ids
,
kill -l
,
kill -signal
process_ids
Kills the specified processes, prints a list of available signals, or sends the specified processes the specified signal (given as a number or name).
program
,
killall -signal
program
Kills all processes that are instances of the specified program or sends the specified signal to all processes that are instances of the specified program.
file
Lets the user peruse a file
too large to be displayed as a single screen (page) of
output. The less command, which is
more powerful than the more command,
provides many subcommands that let the user navigate the
file
. For example, the spacebar moves forward
one page, the b key moves back one
page, and the q key exits the
program.
URL
old new
,
ln -s
old new
Creates a hard (or soft) link associating a new name with an existing file or directory.
pattern
Locates files with names containing the specified pattern. Uses the database maintained by the updatedb command.
files
job
Cancels printing of the specified print queue entries. Use lpq to determine the contents of the print queue.
files
,
ls -a
files
,
ls -l
files
,
ls -lR
files
Lists (nonhidden) files in the current directory or the specified files or directories. The -a option lists hidden files as well has nonhidden files. The -l option causes the list to include descriptive information, such as file size and modification date. The -R option recursively lists the subdirectories of the specified directories.
Launches a simple mail client that permits sending and receiving email messages.
title
,
man
section title
directories
,
mkdir -p
directories
Creates the specified
directories
. The -p
option causes creation of any parent directories
needed to create a specified directory.
type device
Creates
a filesystem of the specified type
(such as
ext3
or msdos
) on the
specified device
(requires root
privileges).
device
Creates
a Linux swap space on the specified hard disk partition (requires
root
privileges).
file
Lets
the user peruse a file
too large to be displayed
as a single screen (page) of output. The more command provides many subcommands that
let the user navigate the file. For example, the spacebar moves
forward one page, the b key moves
back one page, and the q key exits
the program.
device directory
,
mount -o
option
-t
type device directory
Displays
the mounted devices or mounts the specified device at the specified
mount point (generally a subdirectory of /mnt
).
The mount command consults /etc/fstab
to
determine standard options associated with a device. The command
generally requires root privileges. The -o
option allows specification of a variety of options, for
example, ro
for read-only access. The -t option allows specification of the
filesystem type (for example, ext3
,
msdos
, or iso9660
, the
filesystem type generally used for CD-ROMs).
paths target
Moves
the specified files or directories to the specified
target
.
group
user
Changes
the current user’s password or that of the specified
user
(requires root
privileges). The command prompts for the new password.
file
ip_address
,
ping
host
Sends an echo
request via TCP/IP to the specified host
. A
response confirms that the host is operational.
files
Formats the specified
files
for printing, by inserting page breaks and
so on. The command provides many arguments and functions.
Displays
the processes associated with the current userid
or displays a description of each process.
Displays the absolute path corresponding to the current working directory.
files
,
rm -f
files
,
rm -i
files
,
rm -if
files
,
rm -rf
files
Deletes
the specified files
or (when the -r option is specified) recursively deletes all
subdirectories of the specified files and directories. The -f option suppresses confirmation; the
-i option causes the command to
prompt for confirmation. Because deleted files cannot generally be
recovered, the -f option should be
used only with extreme care, particularly when used by the
root
user.
directories
,
rmdir -p
directories
Deletes
the specified empty directories
or (when the
-p option is specified) the empty
directories along the specified path.
host1:file host2:
minutes
,
shutdown -h
minutes
,
shutdown -r
minutes
Shuts down
the system after the specified number of minutes
elapses (requires root
privileges). The
-r option causes the system to be
rebooted once it has shut down. If the -r
option is absent, the system is halted and powered off;
the -h option also halts and shuts
down the system. Alternatively, now
can be used instead of minutes
, which forces an
immediate reboot or halt of the system.
time
Causes the command interpreter to pause for the specified number of seconds.
files
Sorts the
specified files
. The command has many useful
arguments; see the online documentation.
file
Splits
a file
into several smaller files. The command
has many arguments; see the online documentation.
host -
l
userid
user
,
su -
,
su -
user
Changes
the current userid
to root or to the specified
userid
(the latter requires root
privileges). The -option
establishes a default environment for the new
userid
.
device
Disables use of the specified
device
for swapping (requires root
privileges).
device
Enables use
of the specified device
for swapping (requires
root
privileges).
Completes all pending input/output
operations (requires root
privileges).
file
,
tail -f
file
,
tail -n
file
Displays the last several lines of the
specified files
. The -f
option causes the command to continuously print additional
lines as they are written to the file
. The
-n option specifies the number of
lines to be printed.
user
Launches a program
that allows a chatlike dialog with the specified
user
.
tar_file files
,
tar zcvf
tar_file files
Creates a tar file
with the specified name, containing the specified files
and their subdirectories. The z
option specifies that the tarfile will be compressed.
tar_file
,
tar zxvf
tar_file
Extracts the contents of the specified tarfile
.
The z option specifies that the
tarfile has been compressed.
host
Displays a display of system processes that’s continually updated until the user presses the q key.
file
Changes file
access
time. If the specified file
does not exist, the
command creates an empty (new) file.
host
Uses echo requests to determine and print
a network path to the host
.
mask
Specifies default permissions assigned to created directories and files.
device
Unmounts
the specified filesystem (generally requires root
privileges).
file
Displays a message to each user except those who’ve disabled message reception. Type Ctrl-D to end the message.
files
Displays the number of characters, words,
and lines in the specified files
.
file
Table E-1 identifies Linux commands that perform functions similar to MS-DOS commands. The operation of the Linux command is not generally identical to that of the corresponding MS-DOS command. See the index to this book or the Linux online documentation for further information about Linux commands.