The following list describes some of the most useful and popular Linux commands. Consult the man page for each command to learn about additional arguments and details of operation.
-
adduser
userid -
Creates a new userid, prompting for necessary information (requires
root privileges).
-
apropos
keyword -
Searches the manual pages for occurrences of the specified keyword and prints short descriptions from the beginning of matching manual pages.
-
at
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.
-
atq -
Prints descriptions of jobs pending via the
at command.
-
atrm
job -
Cancels execution of a job scheduled via the
at command. Use the
atq command to discover the identities of scheduled jobs.
-
bg -
bg
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.
-
cal
month year -
Prints a calendar for the specified month of the specified year.
-
cat
files -
Prints the contents of the specified files.
-
cd -
cd
directory -
Changes the current working directory to the user's home directory or the specified directory.
-
chgrp
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.
-
chmod
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.
-
chown
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
-
clear -
Clears the terminal screen.
-
cmp
file1 file2 -
Compares two files, reporting all discrepancies. Similar to the
diff command, though the output format differs.
-
cp
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 -
date
date -
Displays the current date and time or changes the system date and time to the specified value, of the form
MMddhhmmyy or
MMddhhmmyyyy.
-
df -
Prints the amount of free disk space on each mounted filesystem.
-
diff
file1 file2 -
Compares two files, reporting all discrepancies. Similar to the
cmp command, though the output format differs.
-
dmesg -
Prints the messages resulting from the most recent system boot.
-
du -
du
directories -
Prints the amount of disk space used by the current directory (or the specified directories) and its (their) subdirectories.
-
echo
string -
echo -n
string -
Prints the specified text on the standard output stream. The
-n option causes omission of the trailing newline character.
-
fdformat
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.
-
fdisk
device -
Edits the partition table of the specified hard disk.
-
fg -
fg
jobs -
Brings the current job (or the specified jobs) to the foreground.
-
file
files -
Determines and prints a description of the type of each specified file.
-
find
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.
-
finger
users -
Prints descriptions of the specified users.
-
free -
Displays the amount of used and free system memory.
-
ftp
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.
-
grep
pattern files -
grep -i
pattern files -
grep -n
pattern files -
grep -v
pattern files -
Search the specified files for text matching the specified pattern (usually enclosed in single quotes) and print 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 file name and line number. The
-v option reverses the matching, causing non-matched lines to be printed.
-
gzip
files -
gunzip
files -
Compress (or expand) the specified files. Generally, a compressed file has the same name as the original file, followed by .
gz.
-
head
files -
Prints the first several lines of each specified file.
-
hostname -
hostname
name -
Displays (or sets) the name of the host.
-
info -
Launches the GNU Texinfo help system.
-
init
run_level -
Changes the system run level to the specified value (requires
root privileges).
-
insmod
module -
Dynamically loads the specified module (requires
root privileges).
-
jobs -
Displays all background jobs.
-
ispell
files -
Checks the spelling of the contents of the specified files.
-
kill
process_ids -
kill -
signal
process_ids -
kill -l -
Kills the specified processes, sends the specified processes the specified signal (given as a number or name), or prints a list of available signals.
-
killall
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.
-
ln
old new -
ln -s
old new -
Creates a hard (or soft) link associating a new name with an existing file or directory.
-
locate
pattern -
Locates files with names containing the specified pattern. Uses the database maintained by the
updatedb command.
-
lpq -
Prints the entries of the print queue.
-
lpr
files -
Prints the specified files.
-
lprm
job -
Cancels printing of the specified print queue entries. Use
lpq to determine the contents of the print queue.
-
ls -
ls
files -
ls -a
files -
ls -l
files -
ls -lR
files -
Lists (non-hidden) files in the current directory or the specified files or directories. The
-a option lists hidden files as well has non-hidden 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.
-
mail -
Launches a simple mail client that permits sending and receiving email messages.
-
man
title -
man
section
title -
Prints the specified man page.
-
mkdir
directories -
mkdir -p
directories -
Creates the specified directories. The
-p option causes creation of any parent directories needed to create a specified directory.
-
mkfs -t
type device -
Creates a file system of the specified type (such as
ext2 or
msdos) on the specified device (requires
root privileges).
-
mkswap
device -
Creates a Linux swap space on the specified hard disk partition (requires
root privileges).
-
more
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
Space key moves forward one page, the
b key moves back one page, and the
q key exits the program.
-
mount -
mount
device directory -
mount -o
option
-t
type device directory -
Prints 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,
ext2,
msdos, or
iso9660, the filesystem type generally used for CD-ROMs).
-
mv
paths target -
Moves the specified files or directories to the specified target.
-
newgroup
group -
Creates the specified group.
-
passwd -
passwd
user -
Changes the current user's password, or that of the specified user (requires
root privileges). The command prompts for the new password.
-
ping
host -
Sends an echo request via TCP/IP to the specified host. A response confirms that the host is operational.
-
pr
files -
Formats the specified files for printing, by inserting page breaks and so on. The command provides many arguments and functions.
-
ps -
ps -Aux -
Displays the processes associated with the current userid or displays a description of each process.
-
pwd -
Prints the absolute path corresponding to the current working directory.
-
reboot -
Reboots the system (requires
root privileges).
-
reset -
Clears the terminal screen and resets the terminal status.
-
rm
files -
rm -i
files -
rm -f
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
-i option causes the command to prompt for confirmation; the
-f option suppresses 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.
-
rmdir
directories -
rmdir -p
directories -
Deletes the specified empty directories or (when the
-p option is specified) the empty directories along the specified path.
-
shutdown
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.
-
sleep
time -
Causes the command interpreter to pause for the specified number of seconds.
-
sort
files -
Sorts the specified files. The command has many useful arguments; see the online documentation.
-
split
file -
Splits a file into several smaller files. The command has many arguments; see the online documentation.
-
su -
su
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.
-
swapon
device -
Enables use of the specified device for swapping (requires
root privileges).
-
swapoff
device -
Disables use of the specified device for swapping (requires
root privileges).
-
sync -
Completes all pending input/output operations (requires
root privileges).
-
tail
file -
tail -
n
file -
tail -f
file -
Prints the last several lines of the specified files. The
-n option specifies the number of lines to be printed. The
-f option causes the command to continuously print additional lines as they are written to the file.
-
talk
user -
Launches a program that allows a chat-like dialog with the specified user.
-
tar cvf
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 specified that the tar file will be compressed.
-
tar xvf
tar_file -
tar zxvf
tar_file -
Extracts the contents of the specified tar file. The
z option specified that the tar file has been compressed.
-
telnet
host -
Opens a login session on the specified host.
-
top -
Prints a display of system processes that's continually updated until the user presses the
q key.
-
traceroute
host -
Uses echo requests to determine and print a network path to the host.
-
umount
device -
Unmounts the specified filesystem (generally requires
root privileges).
-
uptime -
Prints the system uptime.
-
w -
Prints the current system users.
-
wall -
Prints a message to each user except those who've disabled message reception. Type
Ctrl-D to end the message.
-
wc
files -
Prints the number of characters, words, and lines in the specified files.
