This post provides a shortcut for the most frequently used linux commands, for a wide variety of situations, from common file handling to checking system load.

The usual Linux command format is:

command -option(s) argument(s)

For example:

$rm -rf test_app

Basic file and tree commands

  • ls
    the list command - functions in the Linux terminal to show all of the major directories filed under a given file system
    -a : show hidden files
    -lah : show file size in kb
    -ltr : Order files based on last modified time

  • cd [location]
    Changes the current working directory. Without an argument, it goes to the user’s home.

  • mv [file] [location]
    Moves a file to another location.
    Also renames a file

  • cp [file] [location]
    Copies a file to the specified location (overwriting the existing file silently).

  • rm [file]
    Removes a file or directory -rf : Removes a directory (recursively and forced, so it will not prompt)

  • mkdir [directory]
    make directory - command allows the user to make a new directory.

  • rmdir [directory]
    remove directory - allows the user to remove an empty directory

  • pwd
    Display the pathname for the current directory

File commands

  • touch [file]
    The touch command - a.k.a. the make file command - allows users to make files using the Linux CLI.

  • cat [file]
    Display file’s contents to terminal

  • less [file]
    View the contents of a file one page at a time

  • tail [file]
    Display the last n lines of a file (the default is 10)

  • file [file]
    Determine what type of data is within a file.

  • find
    Search for files matching a provided pattern.
    -name : find a file by the name
    -iname : find a file by the name ignoring the case 
    $find -iname "users.rb"

    Link with command detailed description: https://www.computerhope.com/unix/ufind.htm http://www.thegeekstuff.com/2009/03/15-practical-linux-find-command-examples/

  • grep
    Search files or output for a particular pattern
    Link with command detailed description:
    https://www.computerhope.com/unix/ugrep.htm
    http://www.thegeekstuff.com/2009/03/15-practical-unix-grep-command-examples/

  • ln [file] [file]
    Create hard or symbolic link between files 
    $ln /path/to/file /path/to/link     #creates a hard link
$ln -s /path/to/file /path/to/link  #creates a symbolic link

    Link with command detailed description:
    https://www.lifewire.com/create-symbolic-links-ln-command-4059723
    https://www.computerhope.com/unix/uln.htm

  • chmod [options] [permissions] [file]
    Makes a file executable and change files’s permissions
    -x : make file executable
    The user can read, write, and execute it; members of your group can read and execute it; and others may only read it: 
    $chmod u=rwx,g=rx,o=r myfile
$chmod 754 myfile
  • chown [options] [file]
    Change who owns a file -R : add recursive permissions 
    $chown foss file.txt
$chown -R foss /files/work
  • tar [options] [file/location]
    command used to work with tarballs ( files compressed in a tarball archive). It can compress and extract files (preserving the file directory structure) from a tarfile (.tar) or tarball (.tar.gz or .tgz)
    To create a new tar file: 
    $tar cvf archive_name.tar dirname/ # creates an archive
$tar xvf archive_name.tar  # unconpress a file
$tar tvf archive_name.tar  # view file contents

    Link with command detailed description:
    http://www.thegeekstuff.com/2010/04/unix-tar-command-examples/

  • gzip [options] [file]
    command used to work with gz compressed files.
    -d : decompress a file 
    $gzip test.txt  # compress a file
$gzip -d test.txt.gz # uncompress a file
  • unzip [options] [file]
    command to uncompress a zip file: 
    $unzip test.zip

  • nano [file]
    Used to edit configuration files.

  • vi [file]
    Used to edit configuration files.

User administration commands

  • sudo [command]
    Executes a command as an administrative user.

  • su
    Switch to another user account.

  • adduser [username]
    Adds a user to the system.

  • adduser [username] [groupname]
    Adds a user to a specific group.

  • passwd
    Change the password or allow (for the system administrator) to change any password.

  • who
    Display who is logged on

Basic admin commands

  • uname
    used to show the information about the system your Linux distro is running -a : show detailed information about the system 
    $uname -a

  • apt-get dist-upgrade
    In addition to performing upgrades, this is used to intelligently handle dependencies.

  • apt-get install [package]
    Installs (or upgrades) packages.

  • apt-get update
    Resynchronize the package index files from their sources.

  • apt-get upgrade
    Installs the newest versions of all packages currently installed.

  • logout
    Logs out of a shell or SSH session.

  • shutdown
    Shutdown the system
    -h : halt the system -h now : shutdown now -h +5 : shutdown the system after 5 minutes -r now : shutdown and restart the system now -Fr : checks the filesystem when restarting 
    $shutdown -h now

  • reboot
    Reboots the system.

  • source [script]
    Forces bash to read the specified script.

Remote

  • ssh [username@ipaddress]
    Logs into a secure shell session
    -l : login user name 
    ssh -l foss remotehost.example.com
  • wget [location]
    Obtains a file from the Internet
    -O : saves the file with a different name 
    $wget http://marcelofossrj.github.io/repos/file.zip
$wget -O file2.zip http://marcelofossrj.github.io/repos/file.zip
  • curl
    a tool to transfer data from or to a server. It supports HTTP, HTTPS, FTP, FTPS, SCP, SFTP, TFTP, DICT, TELNET, LDAP or FILE
    Basic usage: 
    $curl example.com  #shows the http content
$curl example.com > example.html #saves the the content
$curl -o example.html example.com #also saves the content

    Link with command detailed description:
    http://www.slashroot.in/curl-command-tutorial-linux-example-usage

Services and processes commands

  • df
    Display used and available disk space
    -m : show in megabytes
    -h : show output in human form

  • du
    Show how much space each file takes up

  • ps
    Display a snapshot of the currently running processes 
    $ps -ef | more   #view running processes
$ps -efH | more  #view running processes in tree

  • top
    Displays the resources being used on your system. Press q to exit

  • kill
    Stop a process. If the process refuses to stop, use kill -9 pid

  • Service
    Service command is used to run the system V init scripts. i.e Instead of calling the scripts located in the /etc/init.d/ directory with their full path, you can use the service command 
    $sudo service ssh restart
$sudo service nginx stop
$service --status-all
  • free Command used to display the free, used, and swap memory available in the system in bytes
    -g : shows in giga bytes
    -m : shows in mega bytes
    -k : shows in kilo bytes