Linux\UNIX Commands

In earlier post I have explained how to do debugging in the Linux environment. Here I am exploring some important commands which is required to be comfortable with Linux operating system.

Providing some commands and besides that the explaination of the same.

Again, below is a listing of the Unix / Linux commands and a brief explanation of what each command does. Tried to sorted it, alphabetically.

I bet it is going to be very very useful and you would able to get all the content in one place collectively.

Command Description
ac :: Prints statistics about users' connect time.
alias ::Create a name for another command or long command string.
at :: Command scheduler.

base :: name Deletes any specified prefix from a string.
bash :: Command Bourne interpreter
bc :: Calculator.
bdiff :: Compare large files.
bfs :: Editor for large files.
bg :: Continues a program running in the background.
biff :: Enable / disable incoming mail notifications.
break:: Break out of while, for, foreach, or until loop.
bye :: Alias often used for the exit command.

cal :: Calendar
calendar :: Display appointments and reminders.
cancel :: Cancels a print job.
cat :: View and/or modify a file.
cc :: C compiler.
cd :: Change directory.
chdir :: Change directory.
checkeq :: Language processors to assist in describing equations.
checknr :: Check nroff and troff files for any errors.
chfn :: Modify your own information or if super user or root modify another users information.
chgrp :: Change a groups access to a file or directory.
chkey :: Change the secure RPC key pair.
chmod :: Change the permission of a file.
chown :: Change the ownership of a file.
chsh :: Change login shell.
cksum :: Display and calculate a CRC for files.
clear :: Clears screen.
cls :: Alias often used to clear a screen.
cmp :: Compare files.
col :: Reverse line-feeds filter.
comm :: Compare files and select or reject lines that are common.
compress :: Compress files on a computer.
continue :: Break out of while, for, foreach, or until loop.
cp :: Copy files.
cpio :: Creates archived CPIO files.
crontab :: Create and list files that you wish to run on a regular schedule.
csh :: Execute the C shell command interpreter
csplit :: Split files based on context.
ctags :: Create a tag file for use with ex and vi.
cu ::Calls or connects to another Unix system, terminal or non-Unix system.
curl :: Transfer a URL.
cut :: Cut out selected fields of each line of a file.

date :: Tells you the date and time in Unix.
dc :: An arbitrary precision arithmetic package.
df :: Display the available disk space for each mount.
deroff ::Removes nroff/troff, tbl, and eqn constructs.
diff :: Displays two files and prints the lines that are different.
dig ::DNS lookup utility.
dircmp :: Lists the different files when comparing directories.
dirname :: Deliver portions of path names.
dmesg :: Print or control the kernel ring buffer.
dos2unix :: Converts text files between DOS and Unix formats.
dpost :: Translates files created by troff into PostScript.
du :: Tells you how much space a file occupies.

echo ::Displays text after echo to the terminal.
ed ::Line oriented file editor.
egrep :: Search a file for a pattern using full regular expressions.
elm ::Program command used to send and receive e-mail.
emacs :: Text editor.
enable :: Enables / Disables LP printers.
env :: Displays environment variables.
eqn :: Language processors to assist in describing equations.
ex Line- :: editor mode of the vi text editor.
exit :: Exit from a program, shell or log you out of a Unix network.
expr :: Evaluate arguments as an expression.

fc :: The FC utility lists or edits and re-executes, commands previously entered to an interactive sh.
fg :: Continues a stopped job by running it in the foreground
fgrep :: Search a file for a fixed-character string.
file :: Tells you if the object you are looking at is a file or if it is a directory.
find :: Finds one or more files assuming that you know their approximate filenames.
findsmb :: List info about machines that respond to SMB name queries on a subnet.

fmt :: Simple text formatters.
fromdos :: Converts text files between DOS and Unix formats.
fsck :: Check and repair a Linux file system.
ftp :: Enables ftp access to another terminal.

getfacl :: Display discretionary file information.
gprof :: The gprof utility produces an execution profile of a program.
grep :: Finds text within a file.
groupadd :: Creates a new group account.
groupdel :: Enables a super user or root to remove a group.
groupmod :: Enables a super user or root to modify a group.
gunzip :: Expand compressed files.
gview :: A programmers text editor.
gvim ::A programmers text editor.
gzip :: Compress files.

halt :: Stop the computer.
hash :: Remove internal hash table.
hashstat :: Display the hash stats.
head :: Displays the first ten lines of a file, unless otherwise stated.
help :: If computer has online help documentation installed this command will display it.
history :: Display the history of commands typed.

ifconfig :: Sets up network interfaces.
ifdown :: take a network interface down
ifup :: bring a network interface up

join :: Joins command forms together.

keylogin :: Decrypt the user's secret key.
kill :: Cancels a job.
ksh :: Korn shell command interpreter.

ld :: Link-editor for object files.
ldd :: List dynamic dependencies of executable files or shared objects.
less :: Opposite of the more command.
lex :: Generate programs for lexical tasks.
link :: Calls the link function to create a link to a file.
ln :: Creates a link to a file.
locate :: List files in databases that match a pattern.
login :: Signs into a new system.
logname :: Returns users login name.
logout :: Logs out of a system.
lp :: Prints a file on System V systems.
lpadmin :: Configure the LP print service.
lpc :: Line printer control program.
lpq :: Lists the status of all the available printers.
lpr :: Submits print requests.
lprm :: Removes print requests from the print queue.
lpstat :: Lists status of the LP print services.
ls :: Lists the contents of a directory.

mach :: Display the processor type of the current host.
mail :: One of the ways that allows you to read/send E-Mail.
mailcompat :: Provide SunOS 4.x compatibility for the Solaris mailbox format.
mailx :: Mail interactive message processing system.
make :: Executes a list of shell commands associated with each target.
man :: Display a manual of a command.
mesg :: Control if non-root users can send text messages to you.
mkdir :: Create a directory.
mkfs :: Build a Linux file system, usually a hard disk partition.
more :: Displays text one screen at a time.
mount :: Disconnects a file systems and remote resources.
mt :: Magnetic tape control.
mv :: Renames a file or moves it from one directory to another directory.

nc :: TCP/IP swiss army knife.
neqn :: Language processors to assist in describing equations.
netstat :: Shows network status.
newalias :: Install new elm aliases for user and/or system.
newform :: Change the format of a text file.
newgrp :: Log into a new group.
nice :: Invokes a command with an altered scheduling priority.
niscat :: Display NIS+ tables and objects.
nischmod :: Change access rights on a NIS+ object.
nischown :: Change the owner of a NIS+ object.
nischttl :: Change the time to live value of a NIS+ object.
nisdefaults :: Display NIS+ default values.
nisgrep :: Utilities for searching NIS+ tables.
nismatch :: Utilities for searching NIS+ tables.
nispasswd :: Change NIS+ password information.
nistbladm :: NIS+ table administration command.
nmap :: Network exploration tool and security / port scanner.
nohup :: Runs a command even if the session is disconnected or the user logs out.
nroff :: Formats documents for display or line-printer.
nslookup :: Queries a name server for a host or domain lookup.

on :: Execute a command on a remote system, but with the local environment.
onintr :: Shell built-in functions to respond to (hardware) signals.
optisa :: Determine which variant instruction set is optimal to use.
pack Shrinks file into a compressed file.

pagesize :: Display the size of a page of memory in bytes, as returned by getpagesize.
passwd :: Allows you to change your password.
paste :: Merge corresponding or subsequent lines of files.
pax :: Read / write and writes lists of the members of archive files and copy directory hierarchies.
pcat :: Compresses file.
pg :: Files perusal filters for CRTs.
pgrep :: Examine the active processes on the system and reports the process :: IDs of the processes
pine :: Command line program for Internet News and Email.
ping :: Sends ICMP ECHO_REQUEST packets to network hosts.
pkill :: Examine the active processes on the system and reports the poweroff :: Stop the computer.
pr :: Formats a file to make it look better when printed.
printf :: Write formatted output.
ps :: Reports the process status.
pwd :: Print the current working directory.

quit :: Allows you to exit from a program, shell or log you out of a Unix network.

rcp :: Copies files from one computer to another computer.
reboot :: Stop the computer.
red :: Line oriented file editor.
rehash :: Recomputes the internal hash table of the contents of directories listed in the path.
remsh :: Runs a command on another computer.
repeat :: Shell built-in functions to repeatedly execute action(s) for a selected number of times.
rgview :: A programmers text editor.
rgvim :: A programmers text editor.
rlogin :: Establish a remote connection from your terminal to a remote machine.
rm :: Deletes a file without confirmation (by default).
rmail :: One of the ways that allows you to read/send E-Mail.
rmdir :: Deletes a directory.
rn :: Reads newsgroups.
route :: Show / manipulate the IP routing table.
rpcinfo :: Report RPC information.
rsh :: Runs a command on another computer.
rsync :: Faster, flexible replacement for rcp.
rview :: A programmers text editor.
rvim :: A programmers text editor.

s2p :: Convert a sed script into a Perl script.
sag :: Graphically displays the system activity data stored in a binary data file by a previous sar run.
sar :: Displays the activity for the CPU.
script ::Records everything printed on your screen.
sdiff :: Compares two files, side-by-side.
sed :: Allows you to use pre-recorded commands to make changes to text.
sendmail :: Sends mail over the Internet.
set :: Set the value of an environment variable.
setenv :: Set the value of an environment variable.
setfacl :: Modify the Access Control List (ACL) for a file or files.
settime :: Change file access and modification time.
sftp :: Secure file transfer program.
sh :: Runs or processes jobs through the Bourne shell.
shred :: Delete a file securely, first overwriting it to hide its contents.
shutdown :: Turn off the computer immediately or at a specified time.
sleep :: Waits a x amount of seconds.
slogin :: OpenSSH SSH client (remote login program).
smbclient :: An ftp-like client to access SMB/CIFS resources on servers.
sort :: Sorts the lines in a text file.
spell :: Looks through a text file and reports any words that it finds in the text file that are not in the dictionary.
split :: Split a file into pieces.
stat :: Display file or filesystem status.
stop :: Control process execution.
strip :: Discard symbols from object files.
stty :: Sets options for your terminal.
su :: Become super user or another user.
sysinfo :: Get and set system information strings.
sysklogd :: Linux system logging utilities.

tabs :: Set tabs on a terminal.
tail :: Delivers the last part of the file.
talk :: Talk with other logged in users.
tac :: Concatenate and print files in reverse.
tar :: Create tape archives and add or extract files.
tbl :: Preprocessor for formatting tables for nroff or troff.
tcopy :: Copy a magnetic tape.
tcpdump :: Dump traffic on a network.
tee :: Read from an input and write to a standard output or file.
telnet :: Uses the telnet protocol to connect to another remote computer.
time :: Used to time a simple command.
timex :: The timex command times a command; reports process data and system activity.
todos :: Converts text files between DOS and Unix formats.
top :: Display Linux tasks.
touch :: Change file access and modification time.
tput :: Initialize a terminal or query terminfo database.
tr :: Translate characters.
traceroute :: Print the route packets take to network host.
troff :: Typeset or format documents.

ul ::Reads the named filenames or terminal and does underlining.
umask :: Get or set the file mode creation mask.
unalias :: Remove an alias.
unhash :: Remove internal hash table.
uname :: Print name of current system.
uncompress :: Uncompressed compressed files.
uniq :: Report or filter out repeated lines in a file.
unmount :: Crates a file systems and remote resources.
unpack :: Expands a compressed file.
untar :: Create tape archives and add or extract files.
until :: Execute a set of actions while/until conditions are evaluated TRUE.
useradd :: Create a new user or updates default new user information.
userdel :: Remove a users account.
usermod :: Modify a users account.

vacation :: Reply to mail automatically.
vedit :: Screen-oriented (visual) display editor based on ex.
vgrind :: Grind nice program listings
vi :: Screen-oriented (visual) display editor based on ex.
vim :: A programmers text editor.
view :: A programmers text editor.

w :: Show who is logged on and what they are doing.
wait :: Await process completion.
wc :: Displays a count of lines, words, and characters in a file
whereis :: Locate a binary, source, and manual page files for a command.
while :: Repetitively execute a set of actions while/until conditions are evaluated TRUE.
which ::Locate a command.
who ::Displays who is on the system.
whois :: Internet user name directory service.
write ::Send a message to another user.

X :: Execute the X windows system.
xfd ::Display all the characters in an X font.
xlsfonts :: Server font list displayer for X.
xset ::User preference utility for X.
xterm :: Terminal emulator for X.
xrdb :: X server resource database utility.

yacc :: Short for yet another compiler-compiler, yacc is a compiler.
yes :: Repeatedly output a line with all specified STRING(s), or 'y'.
yppasswd :: Changes network password in the NIS database.

zcat :: Compress files.