Linux Commands

What Is Linux?

Linux is an operating system’s kernel. You might have heard of UNIX. Well, Linux is a UNIX clone. But it was actually created by Linus Torvalds from Scratch. Linux is free and open-source, that means that you can simply change anything in Linux and redistribute it in your own name! There are several Linux Distributions, commonly called “distros”.

  • Ubuntu Linux
  • Red Hat Enterprise Linux
  • Linux Mint
  • Debian
  • Fedora

Linux is Mainly used in servers. About 90% of the internet is powered by Linux servers. This is because Linux is fast, secure, and free! The main problem of using Windows servers is their cost. This is solved by using Linux servers. The OS that runs in about 80% of the smartphones in the world, Android, is also made from the Linux kernel. Most of the viruses in the world run on Windows, but not on Linux!

Linux Shell or “Terminal”

So, basically, a shell is a program that receives commands from the user and gives it to the OS to process, and it shows the output. Linux’s shell is its main part. Its distros come in GUI (graphical user interface), but basically, Linux has a CLI (command-line interface). In this tutorial, we are going to cover the basic commands that we use in the shell of Linux.

To open the terminal, press Ctrl+Alt+T in Ubuntu, or press Alt+F2, type in gnome-terminal, and press enter. In Raspberry Pi, type in lxterminal. There is also a GUI way of taking it, but this is better!

A

  • adduser/addgroup
  • agetty
  • alias
  • anacron
  • apropos
  • apt
  • apt-get
  • aptitude
  • arch
  • arp
  • at
  • atq
  • atrm
  • awk

B

  • batch
  • basename
  • bc
  • bg
  • bzip

C

  • cal
  • cat
  • chgrp
  • chmod
  • chown
  • cksum
  • clear
  • cmp
  • comm
  • cp
  • command Run a command – ignoring shell functions •
  • continue to Resume the next iteration of a loop •
  • 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 fil
  • 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 •
  • link Create a link to a file
  • 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)

M

  • 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
  • pv Monitor the progress of data through a pipe
  • 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 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 •
  • sync Synchronize data on disk with memory

T

  • tail Output the last part of file
  • tar Store, list or extract files in an archive
  • tee Redirect output to multiple files
  • test Evaluate a conditional expression
  • time Measure Program running time
  • timeout Run a command with a time limit
  • 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
  • zip Package and compress (archive) files.
  • . Run a command script in the current shell
  • !! Run the last command again
  • ### Comment / Remark

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