A

apropos

          Search Help manual pages (man -k)

apt-get

          Search for and install software packages (Debian)

aptitude

          Search for and install software packages (Debian)

aspell

          Spell Checker

awk

          Find and Replace text, database sort/validate/index

B

basename

          Strip directory and suffix from filenames

bash

          GNU Bourne-Again Shell

bc

          Arbitrary precision calculator language

bg

          Send to background

break

          Exit from a loop

builtin

          Run a shell builtin

bzip2

          Compress or decompress named files

C

cal
Display a calendar
case
Conditionally perform a command
cat
Concatenate and print (display) the content of files
cd
Change Directory
cfdisk
Partition table manipulator for Linux
chgrp
Change group ownership
chmod
Change access permissions
chown
Change file owner and group
chroot
Run a command with a different root directory
chkconfig
System services (runlevel)
cksum
Print CRC checksum and byte counts
clear
Clear terminal screen
cmp
Compare two files
comm
Compare two sorted files line by line
command
Run a command – ignoring shell functions
continue
Resume the next iteration of a loop
cp
Copy one or more files to another location
cron
Daemon to execute scheduled commands
crontab
Schedule a command to run at a later time
csplit
Split a file into context-determined pieces
cut
Divide a file into several parts

D

date
Display or change the date and time
dc
Desk Calculator
dd
Convert and copy a file, write disk headers, boot records
ddrescue
Data recovery tool
declare
Declare variables and give them attributes
df
Display free disk space
diff
Display the differences between two files
diff3
Show differences among three files
dig
DNS lookup
dir
Briefly list directory contents
dircolors
Colour setup for "ls"
dirname
Convert a full pathname to just a path
dirs
Display list of remembered directories
dmesg
Print kernel & driver messages
du
Estimate file space usage

E

echo
Display message on screen
egrep
Search files for lines that match an extended expression
eject
Eject removable media
enable
Enable and disable builtin shell commands
env
Environment variables
ethtool
Ethernet card settings
eval
Evaluate several commands/arguments
exec
Execute a command
exit
Exit the shell
expect
Automate arbitrary applications accessed over a terminal
expand
Convert tabs to spaces
export
Set an environment variable
expr
Evaluate expressions

F

false
Do nothing, unsuccessfully

fdformat
Low-level format a floppy disk

fdisk
Partition table manipulator for Linux
fg
Send job to foreground
fgrep
Search files for lines that match a fixed string
file
Determine file type
find
Search for files that meet a desired criteria
fmt
Reformat paragraph text
fold
Wrap text to fit a specified width
for
Expand words, and execute commands
format
Format disks or tapes
free
Display memory usage
fsck
File system consistency check and repair
ftp
File Transfer Protocol
function
Define Function Macros
fuser
Identify/kill the process that is accessing a file

G

gawk
Find and Replace text within files
getopts
Parse positional parameters
grep
Search files for lines that match a given pattern
groupadd
Add a user security group
groupdel
Delete a group
groupmod
Modify a group
groups
Print group names a user is in
gzip
Compress or decompress named files

H

hash
Remember the full pathname of a name argument
head
Output the first part of files
help
Display help for a built-in command
history
Command History
hostname
Print or set system name

I

iconv
Convert the character set of a file
id
Print user and group id’s
if
Conditionally perform a command
ifconfig
Configure a network interface
ifdown
Stop a network interface
ifup
Start a network interface up
import
Capture an X server screen and save the image to file
install
Copy files and set attributes

J

jobs
List active jobs
join
Join lines on a common field

K

kill
Stop a process from running
killall
Kill processes by name

L

less
Display output one screen at a time
let
Perform arithmetic on shell variables
ln
Create a symbolic link to a file
local
Create variables
locate
Find files
logname
Print current login name
logout
Exit a login shell
look
Display lines beginning with a given string
lpc
Line printer control program
lpr
Off line print
lprint
Print a file
lprintd
Abort a print job
lprintq
List the print queue
lprm
Remove jobs from the print queue
ls
List information about files
lsof
List open files

M

make
Recompile a group of programs
man
Help manual
mkdir
Create new folders
mkfifo
Make FIFOs (named pipes)
mkisofs
Create an hybrid ISO9660/JOLIET/HFS filesystem
mknod
Make block or character special files
more
Display output one screen at a time
mount
Mount a file system
mtools
Manipulate MS-DOS files
mtr
Network diagnostics (traceroute/ping)
mv
Move or rename files or directories
mmv
Mass Move and rename files

N

netstat
Networking information
nice
Set the priority of a command or job
nl
Number lines and write files
nohup
Run a command immune to hangups
notify-send
Send desktop notifications
nslookup
Query Internet name servers interactively

O

open
Open a file in its default application
op
Operator access

P

passwd
Modify a user password
paste
Merge lines of files
pathchk
Check file name portability
ping
Test a network connection
pkill
Stop processes from running
popd
Restore the previous value of the current directory
pr
Prepare files for printing
printcap
Printer capability database
printenv
Print environment variables
printf
Format and print data
ps
Process status
pushd
Save and then change the current directory
pwd
Print Working Directory

Q

quota
Display disk usage and limits
quotacheck
Scan a file system for disk usage
quotactl
Set disk quotas

R

ram
ram disk device
rcp
Copy files between two machines
read
Read a line from standard input
readarray
Read from stdin into an array variable
readonly
Mark variables/functions as readonly
reboot
Reboot the system
rename
Rename files
renice
Alter priority of running processes
remsync
Synchronize remote files via email
return
Exit a shell function
rev
Reverse lines of a file
rm
Remove files
rmdir
Remove folders
rsync
Remote file copy (Synchronize file trees)

S

screen
Multiplex terminal, run remote shells via ssh
scp
Secure copy (remote file copy)
sdiff
Merge two files interactively
sed
Stream Editor
select
Accept keyboard input
seq
Print numeric sequences
set
Manipulate shell variables and functions
sftp
Secure File Transfer Program
shift
Shift positional parameters
shopt
Shell Options
shutdown
Shutdown or restart linux
sleep
Delay for a specified time
slocate
Find files
sort
Sort text files
source
Run commands from a file
split
Split a file into fixed-size pieces
ssh
Secure Shell client (remote login program)
strace
Trace system calls and signals
su
Substitute user identity
sudo
Execute a command as another user
sum
Print a checksum for a file
suspend
Suspend execution of this shell
symlink
Make a new name for a file
sync
Synchronize data on disk with memory

T

tail
Output the last part of file
tar
Tape Archiver
tee
Redirect output to multiple files
test
Evaluate a conditional expression
time
Measure Program running time
times
User and system times
touch
Change file timestamps
top
List processes running on the system
traceroute
Trace Route to Host
trap
Run a command when a signal is set(bourne)
tr
Translate, squeeze, and/or delete characters
true
Do nothing, successfully
tsort
Topological sort
tty
Print filename of terminal on stdin
type
Describe a command

U

ulimit
Limit user resources
umask
Users file creation mask
umount
Unmount a device
unalias
Remove an alias
uname
Print system information
unexpand
Convert spaces to tabs
uniq
Uniquify files
units
Convert units from one scale to another
unset
Remove variable or function names
unshar
Unpack shell archive scripts
until
Execute commands (until error)
uptime
Show uptime
useradd
Create new user account
usermod
Modify user account
users
List users currently logged in
uuencode
Encode a binary file
uudecode
Decode a file created by uuencode

V

v
Verbosely list directory contents ("ls -l -b")
vdir
Verbosely list directory contents ("ls -l -b")
vi
Text Editor
vmstat
Report virtual memory statistics

W

wait
Wait for a process to complete
watch
Execute/display a program periodically
wc
Print byte, word, and line counts
whereis
Search the user’s $path, man pages and source files for a program
which
Search the user’s $path for a program file
while
Execute commands
who
Print all usernames currently logged in
whoami
Print the current user id and name ("id -un")
wget
Retrieve web pages or files via HTTP, HTTPS or FTP
write
Send a message to another user

X

xargs
Execute utility, passing constructed argument lists
xdg-open
Open a file or URL in the user’s preferred application

Y

yes
Print a string until interrupted