A To Z List of Linux Commands

Linux Commands – A

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

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

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

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

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

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

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

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

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

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

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

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 more command.
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

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

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

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

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

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

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

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

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

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

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

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

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

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

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.

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