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.