The Commands and their Uses are Below… (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 file(s)
(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 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 file(s) 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 file(s) 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 file(s) getopts Parse positional parameters grep Search file(s) 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 file(s)
(H) hash Remember the full pathname of a name argument head Output the first part of file(s) 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 file(s) lsof List open files
(M) make Recompile a group of programs man Help manual mkdir Create new folder(s) 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 psb> Process status pushd Save and then change the current directory pwd Print Working Directory
(Q) quota Display disk usage and limits 9 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 folder(s) 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 userdel Delete a 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 list(s) xdg-open Open a file or URL in the user’s preferred application. yes Print a string until interrupted
Some Exanples and their Usage: Command: ls The command “ls” stands for (List Directory Contents), List the contents of the folder, be it file or folder, from which it runs. The most common options are -a (all files) and -l (long or details) Tab completion is supported and may be configured with .inputrc When output to file the files are listed one per line. By default, colour is not used to distinguish types of files. That is equivalent to using — color=none. Using the –color option without the optional WHEN argument is equivalent to using –color=always. With –color=auto, color codes are output only if standard output is connected to a terminal (tty). 14 Command: lsblk The “lsblk” stands for (List Block Devices), print block devices by their assigned name (but not RAM) on the standard output in a tree-like fashion. he “lsblk -l” command list block devices in „list„ structure (not tree like fashion). Note: lsblk is very useful and easiest way to know the name of New Usb Device you just plugged in, especially when you have to deal with disk/blocks in terminal. Command: sudo he “sudo” (super user do) command allows a permitted user to execute a command as the superuser or another user, as specified by the security policy in the sudoers list. exp: [email protected]:~# sudo add-apt-repository ppa:tualatrix/ppa Note: sudo allows user to borrow superuser privileged, while a similar command „su„ allows user to actually log in as superuser. Sudo is safer than su. It is not advised to use sudo or su for day-to-day normal use, as it can result in serious error if accidentally you did something wrong, that‟s why a very popular saying in Linux community is: “To err is human, but to really foul up everything, you need root password.”
Command: mkdir The “mkdir” (Make directory) command create a new directory with name path. However is the directory already exists, it will return an error message “cannot create folder, folder already exists”. exp: [email protected]:~# mkdir Kalitut Note: Directory can only be created inside the folder, in which the user has write permission. mkdir: cannot create directory `Kalitut„: File exists (Don‟t confuse with file in the above output, you might remember what i said at the beginning – In Linux every file, folder, drive, command, scripts are treated as file). Command: chmod The Linux “chmod” command stands for (change file mode bits). chmod changes the file mode (permission) of each given file, folder, script, etc.. according to mode asked for. There exist 3 types of permission on a file (folder or anything but to keep things simple we will be using file). Read (r)=4 Write(w)=2 Execute(x)=1 So if you want to give only read permission on a file it will be assigned a value of „4„, for write permission only, a value of „2„ and for execute permission only, a value of „1„ is to be given. For read and write permission 4+2 = „6„ is to be given, ans so on. Now permission need to be set for 3 kinds of user and usergroup. The first is owner, then usergroup and finally world. rwxr-x–x abc.sh Here the root‟s permission is rwx (read, write and execute). usergroup to which it belongs, is r-x (read and execute only, no write permission) and for world is –x (only execute). To change its permission and provide read, write and execute permission to owner, group and world. [email protected]:~# chmod 777 abc.sh only read and write permission to all three. [email protected]:~# chmod 666 abc.sh read, write and execute to owner and only execute to group and world. [email protected]:~# chmod 711 abc.sh Note: one of the most important command useful for sysadmin and user both. On a multi-user environment or on a server, this command comes to rescue, setting wrong permission will either makes a file inaccessible or provide unauthorized access to someone. Command: tar The “tar” command is a Tape Archive is useful in creation of archive, in a number of file format and their extraction. [email protected]:~# tar -zxvf abc.tar.gz (Remember ‘z’ for .tar.gz) [email protected]:~# tar -jxvf abc.tar.bz2 (Remember ‘j’ for .tar.bz2) [email protected]:~# tar -cvf archieve.tar.gz(.bz2) /path/to/folder/abc Note: A „tar.gz„ means gzipped. „tar.bz2„ is compressed with bzip which uses a better but slower compression method. Command: cp The “copy” stands for (Copy), it copies a file from one location to another location. [email protected]:~# cp /home/user/Downloads abc.tar.gz /home/user/Desktop (Return 0 when sucess) Note: cp is one of the most commonly used command in shell scripting and it can be used with wildcard characters (Describe in the above block), for customised and desired file copying. Command: mv The “mv” command moves a file from one location to another location. [email protected]:~# mv /home/user/Downloads abc.tar.gz /home/user/Desktop (Return 0 when sucess) Note: mv command can be used with wildcard characters. mv should be used with caution, as moving of system/unauthorised file may lead to security as well as breakdown of system. Command: pwd The command “pwd” (print working directory), prints the current working directory with full path name from terminal. [email protected]:~# pwd /home/user/Desktop Note: This command won‟t be much frequently used in scripting but it is an absolute life saver for newbie who gets lost in terminal in their early connection with nux. (Linux is most commonly referred as nux or nix). Command: cd Finally, the frequently used “cd” command stands for (change directory), it change the working directory to execute, copy, move write, read, etc. from terminal itself. [email protected]:~# cd /home/user/Desktop [email protected]:~$ pwd /home/user/Desktop Note: cd comes to rescue when switching between directories from terminal. “Cd ~” will change the working directory to user‟s home directory, and is very useful if a user finds himself lost in terminal. “Cd ..” will change the working directory to parent directory (of current working directory).
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