The Ultimate A To Z List of Linux Commands | Linux Command Line Reference

Linux Commands – A

Command	Description
accept	Accept or Reject jobs to a destination, such as a printer.
access	Check a user’s RWX permission for a file.
aclocal	GNU autoconf too
aconnect	ALSA sequencer connection manager.
acpi	Show information about the Advanced Configuration and Power Interface.
acpi_available	Check if ACPI functionality exists on the system.
acpid	Informs user-space programs about ACPI events.
addr2line	Used to convert addresses into file names and line numbers.
addresses	Formats for internet mail addresses.
agetty	An alternative Linux Getty
alias	Create an alias for Linux commands
alsactl	Access advanced controls for ALSA soundcard driver.
amidi	Perform read/write operation for ALSA RawMIDI ports.
amixer	Access CLI-based mixer for ALSA soundcard driver.
anacron	Used to run commands periodically.
aplay	Sound recorder and player for CLI.
aplaymidi	CLI utility used to play MIDI files.
apm	Show Advanced Power Management (APM) hardware info on older systems.
apmd	Used to handle events reported by APM BIOS drivers.
apropos	Shows the list of all man pages containing a specific keyword
apt	Advanced Package Tool, a package management system for Debian and derivatives.
apt-get	Command-line utility to install/remove/update packages based on APT system.
aptitude	Another utility to add/remove/upgrade packages based on the APT system.
ar	A utility to create/modify/extract from archives.
arch	Display print machine hardware name.
arecord	Just like aplay, it’s a sound recorder and player for ALSA soundcard driver.
arecordmidi	Record standard MIDI files.
arp	Used to make changes to the system’s ARP cache
as	A portable GNU assembler.
aspell	An interactive spell checker utility.
at	Used to schedule command execution at specified date & time, reading commands from an input file.
atd	Used to execute jobs queued by the at command.
atq	List a user’s pending jobs for the at command.
atrm	Delete jobs queued by the at command.
audiosend	Used to send an audio recording as an email.
aumix	An audio mixer utility.
autoconf	Generate configuration scripts from a TEMPLATE-FILE and send the output to standard output.
autoheader	Create a template header for configure.
automake	Creates GNU standards-compliant Makefiles from template files
autoreconf	Update generated configuration files.
autoscan	Generate a preliminary configure.in
autoupdate	Update a configure.in file to newer autoconf.
awk	Used to find and replace text in a file(s).

Linux Commands – B

Command	Description
badblocks	Search a disk partition for bad sectors.
banner	Used to print characters as a poster.
basename	Used to display filenames with directoy or suffix.
bash	GNU Bourne-Again Shell.
batch	Used to run commands entered on a standard input.
bc	Access the GNU bc calculator utility.
bg	Send processes to the background.
biff	Notify about incoming mail and sender’s name on a system running comsat server.
bind	Used to attach a name to a socket.
bison	A GNU parser generator, compatible with yacc.
break	Used to exit from a loop (eg: for, while, select).
builtin	Used to run shell builtin commands, make custom functions for commands extending their functionality.
bzcmp	Used to call the cmp program for bzip2 compressed files.
bzdiff	Used to call the diff program for bzip2 compressed files.
bzgrep	Used to call grep for bzip2 compressed files.
bzip2	A block-sorting file compressor used to shrink given files.
bzless	Used to apply ‘less’ (show info one page at a time) to bzip2 compressed files.
bzmore	Used to apply ‘more’ (an inferior version of less) to bzip2 compressed files.

Linux Commands – C

Command	Description
cal	Show calendar.
cardctl	Used to control PCMCIA sockets and select configuration schemes.
cardmgr	Keeps an eye on the added/removes sockets for PCMCIA devices.
case	Execute a command conditionally by matching a pattern.
cat	Used to concatenate files and print them on the screen.
cc	GNU C and C++ compiler.
cd	Used to change directory.
cdda2wav	Used to rip a CD-ROM and make WAV file.
cdparanoia	Record audio from CD more reliably using data-verification algorithms.
cdrdao	Used to write all the content specified to a file to a CD all at once.
cdrecord	Used to record data or audio compact discs.
cfdisk	Show or change the disk partition table.
chage	Used to change user password information.
chattr	Used to change file attributes.
chdir	Used to change active working directory.
chfn	Used to change real user name and information.
chgrp	Used to change group ownership for file.
chkconfig	Manage execution of runlevel services.
chmod	Change access permission for a file(s).
chown	Change the owner or group for a file.
chpasswd	Update password in a batch.
chroot	Run a command with root privileges.
chrt	Alter process attributed in real-time.
chsh	Switch login shell.
chvt	Change foreground virtual terminal.
cksum	Perform a CRC checksum for files.
clear	Used to clear the terminal window.
cmp	Compare two files (byte by byte).
col	Filter reverse (and half-reverse) line feeds from the input.
colcrt	Filter nroff output for CRT previewing.
colrm	Remove columns from the lines of a file.
column	A utility that formats its input into columns.
comm	Used to compare two sorted files line by line.
command	Used to execute a command with arguments ignoring shell function named command.
compress	Used to compress one or more file(s) and replacing the originals ones.
continue	Resume the next iteration of a loop.
cp	Copy contents of one file to another.
cpio	Copy files from and to archives.
cpp	GNU C language processor.
cron	A daemon to execute scheduled commands.
crond	Same work as cron.
crontab	Manage crontab files (containing schedules commands) for users.
csplit	Split a file into sections on the basis of context lines.
ctags	Make a list of functions and macro names defined in a programming source file.
cupsd	A scheduler for CUPS.
curl	Used to transfer data from or to a server using supported protocols.
cut	Used to remove sections from each line of a file(s).
cvs	Concurrent Versions System. Used to track file versions, allow storage/retrieval of previous versions, and enables multiple users to work on the same file.

Linux Commands – D

Command	Description
date	Show system date and time.
dc	Desk calculator utility.
dd	Used to convert and copy a file, create disk clone, write disk headers, etc.
ddrescue	Used to recover data from a crashed partition.
deallocvt	Deallocates kernel memory for unused virtual consoles.
debugfs	File system debugger for ext2/ext3/ext4
declare	Used to declare variables and assign attributes.
depmod	Generate modules.dep and map files.
devdump	Interactively displays the contents of device or file system ISO.
df	Show disk usage.
diff	Used to compare files line by line.
diff3	Compare three files line by line.
dig	Domain Information Groper, a DNS lookup utility.
dir	List the contents of a directory.
dircolors	Set colors for ‘ls’ by altering the LS_COLORS environment variable.
dirname	Display pathname after removing the last slash and characters thereafter.
dirs	Show the list of remembered directories.
disable	Restrict access to a printer.
dlpsh	Interactive Desktop Link Protocol (DLP) shell for PalmOS.
dmesg	Examine and control the kernel ring buffer.
dnsdomainname	Show the DNS domain name of the system.
dnssec-keygen	Generate encrypted Secure DNS keys for a given domain name.
dnssec-makekeyset	Produce domain key set from one or more DNS security keys generated by dnssec-keygen.
dnssec-signkey	Sign a secure DNS keyset with key signatures specified in the list of key-identifiers.
dnssec-signzone	Sign a secure DNS zonefile with the signatures in the specified list of key-identifiers.
doexec	Used to run an executable with an arbitrary argv list provided.
domainname	Show or set the name of current NIS (Network Information Services) domain.
dosfsck	Check and repair MS-DOS file systems.
du	Show disk usage summary for a file(s).
dump	Backup utility for ext2/ext3 file systems.
dumpe2fs	Dump ext2/ext3/ext4 file systems.
dumpkeys	Show information about the keyboard driver’s current translation tables.

Linux Commands – E

Command	Desription
e2fsck	Used to check ext2/ext3/ext4 file systems.
e2image	Store important ext2/ext3/ext4 filesystem metadata to a file.
e2label	Show or change the label on an ext2/ext3/ext4 filesystem.
echo	Send input string(s) to standard output i.e. display text on the screen.
ed	GNU Ed – a line-oriented text editor.
edquota	Used to edit filesystem quotas using a text editor, such as vi.
egrep	Search and display text matching a pattern.
eject	Eject removable media.
elvtune	Used to set latency in the elevator algorithm used to schedule I/O activities for specified block devices.
emacs	Emacs text editor command line utility.
enable	Used to enable/disable shell builtin commands.
env	Run a command in a modified environment. Show/set/delete environment variables.
envsubst	Substitute environment variable values in shell format strings.
esd	Start the Enlightenment Sound Daemon (EsounD or esd). Enables multiple applications to access the same audio device simultaneously.
esd-config	Manage EsounD configuration.
esdcat	Use EsounD to send audio data from a specified file.
esdctl	EsounD control program.
esddsp	Used to reroute non-esd audio data to esd and control all the audio using esd.
esdmon	Used to copy the sound being sent to a device. Also, send it to a secondary device.
esdplay	Use EsounD system to play a file.
esdrec	Use EsounD to record audio to a specified file.
esdsample	Sample audio using esd.
etags	Used to create a list of functions and macros from a programming source file. These etags are used by emacs. For vi, use ctags.
ethtool	Used to query and control network driver and hardware settings.
eval	Used to evaluate multiple commands or arguments are once.
ex	Interactive command
exec	An interactive line-based text editor.
exit	Exit from the terminal.
expand	Convert tabs into spaces in a given file and show the output.
expect	An extension to the Tcl script, it’s used to automate interaction with other applications based on their expected output.
export	Used to set an environment variable.
expr	Evaluate expressions and display them on standard output.

Linux Commands – F

Command	Description
factor	Display prime factors of specified integer numbers.
false	Do nothing, unsuccessfully. Exit with a status code indicating failure.
fc-cache	Make font information cache after scanning the directories.
fc-list	Show the list of available fonts.
fdformat	Do a low-level format on a floppy disk.
fdisk	Make changes to the disk partition table.
fetchmail	Fetch mail from mail servers and forward it to the local mail delivery system.
fg	Used to send a job to the foreground.
fgconsole	Display the number of the current virtual console.
fgrep	Display lines from a file(s) that match a specified string. A variant of grep.
file	Determine file type for a file.
find	Do a file search in a directory hierarchy.
finger	Display user data including the information listed in .plan and .project in each user’s home directory.
fingerd	Provides a network interface for the finger program.
flex	Generate programs that perform pattern-matching on text.
fmt	Used to convert text to a specified width by filling lines and removing new lines, displaying the output.
fold	Wrap input line to fit in a specified width.
for	Expand words and run commands for each one in the resultant list.
formail	Used to filter standard input into mailbox format.
format	Used to format disks.
free	Show free and used system memory.
fsck	Check and repair a Linux file system
ftp	File transfer protocol user interface.
ftpd	FTP server process.
function	Used to define function macros.
fuser	Find and kill a process accessing a file.

Linux Commands – G

Command	Description
g++	Run the g++ compiler.
gawk	Used for pattern scanning and language processing. A GNU implementation of AWK language.
gcc	A C and C++ compiler by GNU.
gdb	A utility to debug programs and know about where it crashes.
getent	Shows entries from Name Service Switch Libraries for specified keys.
getkeycodes	Displays the kernel scancode-to-keycode mapping table.
getopts	A utility to parse positional parameters.
gpasswd	Allows an administrator to change group passwords.
gpg	Enables encryption and signing services as per the OpenPGP standard.
gpgsplit	Used to split an OpenPGP message into packets.
gpgv	Used to verify OpenPGP signatures.
gpm	It enables cut and paste functionality and a mouse server for the Linux console.
gprof	Shows call graph profile data.
grep	Searches input files for a given pattern and displays the relevant lines.
groff	Serves as the front-end of the groff document formatting system.
groffer	Displays groff files and man pages.
groupadd	Used to add a new user group.
groupdel	Used to remove a user group.
groupmod	Used to modify a group definition.
groups	Show the group(s) to which a user belongs.
grpck	Verifies the integrity of group files.
grpconv	Creates a gshadow file from a group or an already existing gshadow.
gs	Invokes Ghostscript, and interpreter and previewer for Adobe’s PostScript and PDF languages.
gunzip	A utility to compress/expand files.
gzexe	Used compress executable files in place and have them automatically uncompress and run at a later stage.
gzip	Same as gzip.

Linux Commands – H

Command	Description
halt	Command used to half the machine.
hash	Shows the path for the commands executed in the shell.
hdparm	Show/configure parameters for SATA/IDE devices.
head	Shows first 10 lines from each specified file.
help	Display’s help for a built-in command.
hexdump	Shows specified file output in hexadecimal, octal, decimal, or ASCII format.
history	Shows the command history.
host	A utility to perform DNS lookups.
hostid	Shows host’s numeric ID in hexadecimal format.
hostname	Display/set the hostname of the system.
htdigest	Manage the user authentication file used by the Apache web server.
htop	An interactive process viewer for the command line.
hwclock	Show or configure the system’s hardware clock.

Linux Commands – I

Command	Description
iconv	Convert text file from one encoding to another.
id	Show user and group information for a specified user.
if	Execute a command conditionally.
ifconfig	Used to configure network interfaces.
ifdown	Stops a network interface.
ifup	Starts a network interface.
imapd	An IMAP (Interactive Mail Access Protocol) server daemon.
import	Capture an X server screen and saves it as an image.
inetd	Extended internet services daemon, it starts the programs that provide internet services.
info	Used to read the documentation in Info format.
init	Systemd system and service manager.
insmod	A program that inserts a module into the Linux kernel.
install	Used to copy files to specified locations and set attributions during the install process.
iostat	Shows statistics for CPU, I/O devices, partitions, network filesystems.
ip	Display/manipulate routing, devices, policy, routing and tunnels.
ipcrm	Used to remove System V interprocess communication (IPC) objects and associated data structures.
ipcs	Show information on IPC facilities for which calling process has read access.
iptables	Administration tool for IPv4 packet filtering and NAT.
iptables-restore	Used to restore IP tables from data specified in the input or a file.
iptables-save	Used to dump IP table contents to standard output.
isodump	A utility that shows the content iso9660 images to verify the integrity of directory contents.
isoinfo	A utility to perform directory like listings of iso9660 images.
isosize	Show the length of an iso9660 filesystem contained in a specified file.
isovfy	Verifies the integrity of an iso9660 image.
ispell	A CLI-based spell-check utility.

Linux Commands – J

Command	Description
jobs	Show the list of active jobs and their status.
join	For each pair of input lines, join them using a command field and display on standard output.

Linux Commands – K

Command	Description
kbd_mode	Set a keyboard mode. Without arguments, shows the current keyboard mode.
kbdrate	Reset keyboard repeat rate and delay time.
kill	Send a kill (termination) signal to one more processes.
killall	Kills a process(es) running a specified command.
killall5	A SystemV killall command. Kills all the processes excluding the ones which it depends on.
klogd	Control and prioritize the kernel messages to be displayed on the console, and log them through syslogd.
kudzu	Used to detect new and enhanced hardware by comparing it with existing database. Only for RHEL and derivates.

Linux Commands – L

Command	Description
last	Shows a list of recent logins on the system by fetching data from /var/log/wtmp file.
lastb	Shows the list of bad login attempts by fetching data from /var/log/btmp file.
lastlog	Displays information about the most recent login of all users or a specified user.
ld	The Unix linker, it combines archives and object files. It then puts them into one output file, resolving external references.
ldconfig	Configure dynamic linker run-time bindings.
ldd	Shows shared object dependencies.
less	Displays contents of a file one page at a time. It’s advanced than morecommand.
lesskey	Used to specify key bindings for less command.
let	Used to perform integer artithmetic on shell variables.
lftp	An FTP utility with extra features.
lftpget	Uses lftop to retrieve HTTP, FTP, and other protocol URLs supported by lftp.
link	Create links between two files. Similar to ln command.
ln	Create links between files. Links can be hard (two names for the same file) or soft (a shortcut of the first file).
loadkeys	Load keyboard translation tables.
local	Used to create function variables.
locale	Shows information about current or all locales.
locate	Used to find files by their name.
lockfile	Create semaphore file(s) which can be used to limit access to a file.
logger	Make entries in the system log.
login	Create a new session on the system.
logname	Shows the login name of the current user.
logout	Performs the logout operation by making changes to the utmp and wtmp files.
logrotate	Used for automatic rotation, compression, removal, and mailing of system log files.
look	Shows any lines in a file containing a given string in the beginning.
losetup	Set up and control loop devices.
lpadmin	Used to configure printer and class queues provided by CUPS (Common UNIX Printing System).
lpc	Line printer control program, it provides limited control over CUPS printer and class queues.
lpinfo	Shows the list of avaiable devices and drivers known to the CUPS server.
lpmove	Move on or more printing jobs to a new destination.
lpq	Shows current print queue status for a specified printer.
lpr	Used to submit files for printing.
lprint	Used to print a file.
lprintd	Used to abort a print job.
lprintq	List the print queue.
lprm	Cancel print jobs.
lpstat	Displays status information about current classes, jobs, and printers.
ls	Shows the list of files in the current directory.
lsattr	Shows file attributes on a Linux ext2 file system.
lsblk	Lists information about all available or the specified block devices.
lsmod	Show the status of modules in the Linux kernel.
lsof	List open files.
lspci	List all PCI devices.
lsusb	List USB devices.

Linux Commands – M

Command	Description
m4	Macro processor.
mail	Utility to compose, receive, send, forward, and reply to emails.
mailq	Shows to list all emails queued for delivery (sendmail queue).
mailstats	Shows current mail statistics.
mailto	Used to send mail with multimedia content in MIME format.
make	Utility to maintain groups of programs, recompile them if needed.
makedbm	Creates an NIS (Network Information Services) database map.
makemap	Creates database maps used by the keyed map lookups in sendmail.
man	Shows manual pages for Linux commands.
manpath	Determine search path for manual pages.
mattrib	Used to change MS-DOS file attribute flags.
mbadblocks	Checks MD-DOS filesystems for bad blocks.
mcat	Dump raw disk image.
mcd	Used to change MS-DOS directory.
mcopy	Used to copy MS-DOS files from or to Unix.
md5sum	Used to check MD5 checksum for a file.
mdel, mdeltree	Used to delete MS-DOS file. mdeltree recursively deletes MS-DOS directory and its contents.
mdir	Used to display an MS-DOS directory.
mdu	Used to display the amount of space occupied by an MS-DOS directory.
merge	Three-way file merge. Includes all changes from file2 and file3 to file1.
mesg	Allow/disallow osends to sedn write messages to your terminal.
metamail	For sending and showing rich text or multimedia email using MIME typing metadata.
metasend	An interface for sending non-text mail.
mformat	Used to add an MS-DOS filesystem to a low-level formatted floppy disk.
mimencode	Translate to/from MIME multimedia mail encoding formats.
minfo	Display parameters of an MS-DOS filesystem.
mkdir	Used to create directories.
mkdosfs	Used to create an MS-DOS filesystem under Linux.
mke2fs	Used create an ext2/ext3/ext4 filesystem.
mkfifo	Used to create named pipes (FIFOs) with the given names.
mkfs	Used to build a Linux filesystem on a hard disk partition.
mkfs.ext3	Same as mke2fs, create an ext3 Linux filesystem.
mkisofs	Used to create an ISO9660/JOLIET/HFS hybrid filesystem.
mklost+found	Create a lost+found directory on a mounted ext2 filesystem.
mkmanifest	Makes a list of file names and their DOS 8.3 equivalent.
mknod	Create a FIFO, block (buffered) special file, character (unbuffered) special file with the specified name.
mkraid	Used to setup RAID device arrays.
mkswap	Set up a Linux swap area.
mktemp	Create a temporary file or directory.
mlabel	Make an MD-DOS volume label.
mmd	Make an MS-DOS subdirectory.
mmount	Mount an MS-DOS disk.
mmove	Move or rename an MS-DOS file or subdirectory.
mmv	Mass move and rename files.
modinfo	Show information about a Linux kernel module.
modprobe	Add or remove modules from the Linux kernel.
more	Display content of a file page-by-page.
most	Browse or page through a text file.
mount	Mount a filesystem.
mountd	NFS mount daemon.
mpartition	Partition an MS-DOS disk.
mpg123	Command-line mp3 player.
mpg321	Similar to mpg123.
mrd	Remove an MS-DOS subdirectory.
mren	Rename an existing MS-DOS file.
mshowfat	Show FTA clusters allocated to a file.
mt	Control magnetic tape drive operation.
mtools	Utilities to access MS-DOS disks.
mtoolstest	Tests and displays the mtools configuration files.
mtr	A network diagnostic tool.
mtype	Display contents of an MS-DOS file.
mv	Move/rename files or directories.
mzip	Change protection mode and eject disk on Zip/Jaz drive.

Linux Commands – N

Command	Description
named	Internet domain name server.
namei	Follow a pathname until a terminal point is found.
nameif	Name network interfaces based on MAC addresses.
nc	Netcat utility. Arbitrary TCP and UDP connections and listens.
netstat	Show network information.
newaliases	Rebuilds mail alias database.
newgrp	Log-in to a new group.
newusers	Update/create new users in batch.
nfsd	Special filesystem for controlling Linux NFS server.
nfsstat	List NFS statistics.
nice	Run a program with modified scheduling priority.
nl	Show numbered line while displaying the contents of a file.
nm	List symbols from object files.
nohup	Run a command immune to hangups.
notify-send	A program to send desktop notifications.
nslookup	Used performs DNS queries. Read this article for more info.
nsupdate	Dynamic DNS update utility.

Linux Commands – O

Command	Description
objcopy	Copy and translate object files.
objdump	Display information from object files.
od	Dump files in octal and other formats.
op	Operator access, allows system administrators to grant users access to certain root operations that require superuser privileges.
open	Open a file using its default application.
openvt	Start a program on a new virtual terminal (VT).

Linux Commands – P

Command	Description
passwd	Change user password.
paste	Merge lines of files. Write to standard output, TAB-separated lines consisting of sqentially correspnding lines from each file.
patch	Apply a patchfile (containing differences listing by diff program) to an original file.
pathchk	Check if file names are valid or portable.
perl	Perl 5 language interpreter.
pgrep	List process IDs matching the specified criteria among all the running processes.
pidof	Find process ID of a running program.
ping	Send ICMP ECHO_REQUEST to network hosts.
pinky	Lightweight finger.
pkill	Send kill signal to processes based on name and other attributes.
pmap	Report memory map of a process.
popd	Removes directory on the head of the directory stack and takes you to the new directory on the head.
portmap	Converts RPC program numbers to IP port numbers.
poweroff	Shuts down the machine.
pppd	Point-to-point protocol daemon.
pr	Convert (column or paginate) text files for printing.
praliases	Prints the current system mail aliases.
printcap	Printer capability database.
printenv	Show values of all or specified environment variables.
printf	Show arguments formatted according to a specified format.
ps	Report a snapshot of the current processes.
ptx	Produce a permuted index of file contents.
pushd	Appends a given directory name to the head of the stack and then cd to the given directory.
pv	Monitor progress of data through a pipe.
pwck	Verify integrity of password files.
pwconv	Creates shadow from passwd and an optionally existing shadow.
pwd	Show current directory.
python

Linux Commands – Q

Command	Description
quota	Shows disk usage, and space limits for a user or group. Without arguments, only shows user quotas.
quotacheck	Used to scan a file system for disk usage.
quotactl	Make changes to disk quotas.
quotaoff	Enable enforcement of filesystem quotas.
quotaon	Disable enforcement of filesystem quotas.
quotastats	Shows the report of quota system statistics gathered from the kernel.

Linux Commands – R

Command	Description
raidstart	Start/stop RAID devices.
ram	RAM disk device used to access the RAM disk in raw mode.
ramsize	Show usage information for the RAM disk.
ranlib	Generate index to the contents of an archive and store it in the archive.
rar	Create and manage RAR file in Linux.
rarpd	Respond to Reverse Address Resoultion Protocol (RARP) requests.
rcp	Remote copy command to copy files between remote computers.
rdate	Set system date and time by fetching information from a remote machine.
rdev	Set or query RAM disk size, image root device, or video mode.
rdist	Remote file distribution client, maintains identical file copies over multiple hosts.
rdistd	Start the rdist server.
read	Read from a file descriptor.
readarray	Read lines from a file into an array variable.
readcd	Read/write compact disks.
readelf	Shows information about ELF (Executable and Linkable fomrat) files.
readlink	Display value of a symbolic link or canonical file name.
readonly	Mark functions and variables as read-only.
reboot	Restart the machine.
reject	Accept/reject print jobs sent to a specified destination.
remsync	Synchronize remote files over email.
rename	Rename one or more files.
renice	Change priority of active processes.
repquota	Report disk usage and quotas for a specified filesystem.
reset	Reinitialize the terminal.
resize2fs	Used to resize ext2/ext3/ext4 file systems.
restore	Restore files from a backup created using dump.
return	Exit a shell function.
rev	Show contents of a file, reversing the order of characters in every line.
rexec	Remote execution client for exec server.
rexecd	Remote execution server.
richtext	View “richtext” on an ACSII terminal.
rlogin	Used to connect a local host system with a remote host.
rlogind	Acts as the server for rlogin. It facilitates remote login, and authentication based on privileged port numbers from trusted hosts.
rm	Removes specified files and directories (not by default).
rmail	Handle remote mail received via uucp.
rmdir	Used to remove empty directories.
rmmod	A program to remove modules from Linux kernel.
rndc	Name server control utility. Send command to a BIND DNS server over a TCP connection.
rootflags	Show/set flags for the kernel image.
route	Show/change IP routing table.
routed	A daemon, invoked at boot time, to manage internet routing tables.
rpcgen	An RPC protocol compiler. Parse a file written in the RPC language.
rpcinfo	Shows RPC information. Makes an RPC call to an RPC server and reports the findings.
rpm	A package manager for linux distributions. Originally developed for RedHat Linux.
rsh	Remote shell. Connects to a specified host and executes commands.
rshd	A daemon that acts as a server for rsh and rcp commands.
rsync	A versitile to for copying files remotely and locally.
runlevel	Shows previous and current SysV runlevel.
rup	Remote status display. Shows current system status for all or specified hosts on the local network.
ruptime	Shows uptime and login details of the machines on the local network.
rusers	Shows the list of the users logged-in to the host or on all machines on the local network.
rusersd	The rsuerd daemon acts as a server that responds to the queries from rsuers command.
rwall	Sends messages to all users on the local network.
rwho	Reports who is logged-in to the hosts on the local network.
rwhod	Acts as a server for rwho and ruptime commands.

Linux Commands – S

Command	Description
sane-find-scanner	Find SCSI and USB scanner and determine their device files.
scanadf	Retrieve multiple images from a scanner equipped with an automatic document feeder (ADF).
scanimage	Read images from image aquistion devices (scanner or camera) and display on standard output in PNM (Portable aNyMap) format.
scp	Copy files between hosts on a network securely using SSH.
screen	A window manager that enables multiple pseudo-terminals with the help of ANSI/VT100 terminal emulation.
script	Used to make a typescript of everything displayed on the screen during a terminal session.
sdiff	Shows two files side-by-side and highlights the differences.
sed	Stream editor for filtering and transforming text (from a file or a pipe input).
select	Synchronous I/O multiplexing.
sendmail	It’s a mail router or an MTA (Mail Transfer Agent). sendmail support can send a mail to one or more recepients using necessary protocols.
sensors	Shows the current readings of all sensor chips.
seq	Displays an incremental sequence of numbers from first to last.
set	Used to manipulate shell variables and functions.
setfdprm	Sets floppy disk parameters as provided by the user.
setkeycodes	Load kernel scancode-to-keycode mapping table entries.
setleds	Show/change LED light settings of the keyboard.
setmetamode	Define keyboard meta key handling. Without arguments, shows current meta key mode.
setquota	Set disk quotas for users and groups.
setsid	Run a program in a new session.
setterm	Set terminal attributes.
sftp	Secure File Transfer program.
sh	Command interpreter (shell) utility.
sha1sum	Compute and check 160-bit SHA1 checksum to verify file integrity.
shift	Shift positional parameters.
shopt	Shell options.
showkey	Examines codes sent by the keyboard displays them in printable form.
showmount	Shows information about NFS server mount on the host.
shred	Overwrite a file to hide its content (optionally delete it), making it harder to recover it.
shutdown	Power-off the machine.
size	Lists section size and the total size of a specified file.
skill	Send a signal to processes.
slabtop	Show kernel slab cache information in real-time.
slattach	Attack a network interface to a serial line.
sleep	Suspend execution for a specified amount of time (in seconds).
slocate	Display matches by searching filename databases. Takes ownership and file permission into consideration.
snice	Reset priority for processes.
sort	Sort lines of text files.
source	Run commands from a specified file.
split	Split a file into pieces of fixed size.
ss	Display socket statistics, similar to netstat.
ssh	An SSH client for logging in to a remote machine. It provides encrypted communication between the hosts.
ssh-add	Adds private key identities to the authentication agent.
ssh-agent	It holds private keys used for public key authentication.
ssh-keygen	It generates, manages, converts authentication keys for ssh.
ssh-keyscan	Gather ssh public keys.
sshd	Server for the ssh program.
stat	Display file or filesystem status.
statd	A daemon that listens for reboot notifications from other hosts, and manages the list of hosts to be notified when the local system reboots.
strace	Trace system calls and signals.
strfile	Create a random access file for storing strings.
strings	Search a specified file and prints any printable strings with at least four characters and followed by an unprintable character.
strip	Discard symbols from object files.
stty	Change and print terminal line settings.
su	Change user ID or become superuser.
sudo	Execute a command as superuser.
sum	Checksum and count the block in a file.
suspend	Suspend the execution of the current shell.
swapoff	Disable devices for paging and swapping.
swapon	Enable devices for paging and swapping.
symlink	Create a symbolic link to a file.
sync	Synchronize cached writes to persistent storage.
sysctl	Configure kernel parameters at runtime.
sysklogd	Linux system logging utilities. Provides syslogd and klogd functionalities.
syslogd	Read and log system messages to the system console and log files.

Linux Commands – T

Command	Description
tac	Concatenate and print files in reverse order. Opposite of cat command.
tail	Show the last 10 lines of each specified file(s).
tailf	Follow the growth of a log file. (Deprecated command)
talk	A two-way screen-oriented communication utility that allows two user to exchange messages simulateneously.
talkd	A remote user communication server for talk.
tar	GNU version of the tar archiving utility. Used to store and extract multiple files from a single archive.
taskset	Set/retrieve a process’s CPU affinity.
tcpd	Access control utility for internet services.
tcpdump	Dump traffic on network. Displays a description of the contents of packets on a network interface that match the boolean expression.
tcpslice	Extract pieces of tcpdump files or merge them.
tee	Read from standard input and write to standard output and files.
telinit	Change SysV runlevel.
telnet	Telnet protocol user interface. Used to interact with another host using telnet.
telnetd	A server for the telnet protocol.
test	Check file type and compare values.
tftp	User interface to the internet TFTP (Trivial File Transfer Protocol).
tftpd	TFTP server.
time	Run programs and summarize system resource usage.
timeout	Execute a command with a time limit.
times	Shows accumulated user and system times for the shell and it’s child processes.
tload	Shows a graph of the current system load average to the specified tty.
tmpwatch	Recursively remove files and directories which haven’t been accessed for the specified period of time.
top	Displays real-time view of processes running on the system.
touch	Change file access and modification times.
tput	Modify terminal-dependent capabilities, color, etc.
tr	Translate, squeeze, or delete characters from standard input and display on standard output.
tracepath	Traces path to a network host discovering MTU (Maximum Transmission Unit) along this path.
traceroute	Traces the route taken by the packets to reach the network host.
trap	Trap function responds to hardware signals. It defines and creates handlers to run when the shell receives signals.
troff	The troff processor of the groff text formatting system.
TRUE	Exit with a status code indicating success.
tset	Initialize terminal.
tsort	Perform topological sort.
tty	Display the filename of the terminal connected to standard input.
tune2fs	Adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems.
tunelp	Set various parameters for the line printer devices.
type	Write a description for a command type.

Linux Commands – U

Command	Description
ul	Underline text.
ulimit	Get and set user limits for the calling process.
umask	Set file mode creation mask.
umount	Unmount specified file systems.
unalias	Remove alias definitions for specified alias names.
uname	Show system information.
uncompress	Uncompress the files compressed with the compress command.
unexpand	Convert spaces to tabs for a specified file.
unicode_start	Put keyboard and console in Unicode mode.
unicode_stop	Revert keyboard and console from Unicode mode.
uniq	Report or omit repeating lines.
units	Convert units from one scalar to another.
unrar	Extract files from a RAR archive.
unset	Remove variable or function names.
unshar	Unpack shell archive scripts.
until	Execute command until a given condition is true.
uptime	Tell how long the system has been running.
useradd	Create a new user or update default user information.
userdel	Delete a user account and related files.
usermod	Modify a user account.
users	Show the list of active users on the machine.
usleep	Suspend execution for microsecond intervals.
uudecode	Decode a binary file.
uuencode	Encode a binary file.
uuidgen	Created a new UUID (Universally Unique Identifier) table.

Linux Commands – V

Command	Description
vdir	Same as ls -l -b. Verbosely list directory contents.
vi	A text editor utility.
vidmode	Set the video mode for a kernel image. Displays current mode value without arguments. Alternative: rdev -v
vim	Vi Improved, a text-based editor which is a successor to vi.
vmstat	Shows information about processes, memory, paging, block IO, traps, disks, and CPU activity.
volname	Returns volume name for a device formatted with an ISO-9660 filesystem. For example, CD-ROM.

Linux Commands – W

Command	Description
w	Show who is logged-on and what they’re doing.
wait	Waits for a specified process ID(s) to terminate and returns the termination status.
wall	Display a message on the terminals all the users who are currently logged-in.
warnquota	Send mail to the users who’ve exceeded their disk quota soft limit.
watch	Runs commands repeatedly until interrupted and shows their output and errors.
wc	Print newline, word, and byte count for each of the specified files.
wget	A non-interactive file download utility.
whatis	Display one line manual page descriptions.
whereis	Locate the binary, source, and man page files for a command.
which	For a given command, lists the pathnames for the files which would be executed when the command runs.
while	Conditionally execute commands (while loop).
who	Shows who is logged on.
whoami	Displays the username tied to the current effective user ID.
whois	Looks for an object in a WHOIS database
write	Display a message on other user’s terminal.

Linux Commands – X

Command	Description
xargs	Runs a command using initial arguments and then reads remaining arguments from standard input.
xdg-open	Used to open a file or URL in an application preferred by the user.
xinetd	Extended internet services daemon. Works similar to inetd.
xz	Compress/ Decompress .xz and .lzma files.

Linux Commands – Y

Command	Description
yacc	Yet Another Compiler Compiler, a GNU Project parser generator.
yes	Repeatedly output a line with a specified string(s) until killed.
ypbind	A daemon that helps client processes to connect to an NIS server.
ypcat	Shows the NIS map (or database) for the specified MapName parameter.
ypinit	Sets up NIS maps on an NIS server.
ypmatch	Shows values for specified keys from an NIS map.
yppasswd	Change NIS login password.
yppasswdd	Acts as a server for the yppasswd command. Receives and executes requests.
yppoll	Shows the ID number or version of NIS map currently used on the NIS server.
yppush	Forces slave NIS servers to copy updated NIS maps.
ypserv	A daemon activated at system startup. It looks for information in local NIS maps.
ypset	Point a client (running ypbind) to a specifc server (running ypserv).
yptest	Calls various functions to check the configuration of NIS services.
ypwhich	Shows the hostname for NIS server or master server for a given map.
ypxfr	Transfers NIS server map from server to a local host.

Linux Commands – Z

Command	Description
zcat	Used to compress/uncompress files. Similar to gzip
zcmp	Compare compressed files.
zdiff	Compare compressed files line by line.
zdump	Displays time for the timezone mentioned.
zforce	Adds .gz extension to all gzipped files.
zgrep	Performs grep on compressed files.
zic	Creates time conversion information files using the specified input files.
zip	A file compression and packaging utility.
zless	Displays information of a compressed file (using less command) on the terminal one screen at a time.
zmore	Displays output of a compressed file (using more command) on the terminal one page at a time.
znew	Recompress .z files to .gz. files.