Linux cheatsheet

This is more of a Ubuntu cheatsheet than a Linux one. However, many shortcuts and commands are usable on other Linux systems.

Most of these are just example usages. You should check each command’s manual for more options (by using the man command).


  • Read the manual of any (supported) command

      man <command>
  • Change the current directory

      cd <path>

    Go to home directory

  • Print the current working directory

  • List files

      ls # List files in the current directory
      ls </path> # List files in a directory
      ls *.md # List files whose extention is `md`
      ls favicon* # List files that starts with `favicon`
      ls -l # List files with more information, like mod, size, owner
      ls -a # List all files, including hidden files

Bash shortcuts

  • Stop current command: <Ctrl> + C
  • Sleep program: <Ctrl> + Z
  • Go to start of line: <Ctrl> + A
  • Go to end of line: <Ctrl> + E
  • Cut from start of line: <Ctrl> + U
  • Cut to end of line: <Ctrl> + V
  • Select text: hold <Shift>, left click then drag your mouse
  • Copy selection: <Ctrl> + <Shift> + C
  • Paste selection: <Ctrl> + <Shift> + V
  • Search for a previously used command: <Ctrl> + R
  • Repeat last command: !!

Users and permissions

  • Check current user’s name

  • Check the id of a user

      id <username>
  • Run a command as root

      sudo <command>
  • Run a command as another user

      sudo -u <username> <command>
  • Switch to another user

      su <username> # This requires the user's password
      sudo su <username> # Root can switch to any user without knowing the password
  • Add a new user

      sudo adduser <username>
  • Add a user into a group

      sudo usermod -aG <groupname> <username>
      sudo adduser <username> <groupname>
  • Delete a user

      sudo userdel <username>
  • Change the user’s password


    Change another user’s password

      sudo passwd <username>
  • Change mod of a file

      sudo chmod <mod> <filepath>


      sudo chmod 600 ~/.ssh/authorized_keys
      sudo chmod +x <path> # make file at <path> executable
      sudo chmod a+x <path> # make file at <path> executable for all users
      sudo chmod -R <mod> <directory_path> # Change mod for all files under <directory>

    Notes: In order to cd to a directory, the directory itself must be executable to the current user

Environment variables

  • Print all environment variables

  • Set an environment variables

      export VARIABLE_NAME=<value> # There should be no spaces before and after `=`
  • Some useful environment variables:

    • $USER: Current user’s name, same as output of whoami
    • $UID: Current user’s id, same as output of id -u $USER
    • $PWD: Path of the current working directory, same as output of pwd
    • $HOME: Current user’s home directory
    • $PATH: A set of directories where executable programs are located. These programs can be called directly without specifying the full path.

Basic programming

  • Create a variables

      VARIABLE_NAME=<value> # There should be no spaces before and after `=`
  • Checking a variable’s value

      echo $VARIABLE_NAME
  • Using variables in commands

      ls $HOME
      cd $HOME
  • Using the stdin output of a command as the argument of another command

      ls `pwd`
  • Piping the output of one command as the input of another command

      command1 .... | command2 ....
  • Redirecting a file or stream

      command .... >/output.log 2>error.log
      command < file.txt
  • Ignore error logs

      command arg1 arg2 arg3... 2>/dev/null
  • Ignore all logs

      command arg1 arg2 arg3... >/dev/null 2>&1
  • Run program in background (it’s still killed if the terminal is closed)

      command arg1 arg2 arg3... &

Files and folder

  • Create an empty file

      touch filename
  • Print content of a file

      cat </path/to/file>
  • Quickly create a file with a short content

      echo "<?php phpinfo(); ?>" > phpinfo.php
  • Appending content to file

      $ echo "1" > test
      $ echo "2" > test
      $ echo "3" >> test
      $ cat test
  • Count number of words in a file

      wc </path/to/file>
  • Using grep to find a pattern in a file in directory

      grep <pattern> </path/to/file>

    Find pattern in all files in a directory recursively

      grep -r <pattern> </path/to/directory>

    Only show file names

      grep -rl <pattern> </path/to/directory>

    Search incasesensitively

      grep -i <pattern> </path/to/file>
  • Using find to find a file

      find </path> -type f -name '<pattern>'

    Or finding a directory

      find </path> -type d -name '<pattern>'
  • Check available diskspace

      df -ah
      du -sh


  • Show system and kernel

      uname -a
  • Check system disk space usage

      df -h
  • Show system date

  • Show uptime

  • Show current free and used memory in the system

      free -m
  • Set the CPU affinity of a process

      taskset 0x01 command # Set the process's CPU's afinity to CPU 1
      taskset 0x03 command # Set the process's CPU's afinity to CPU 1 and 2
      taskset 0x07 command # Set the process's CPU's afinity to CPU 1, 2 and 3
      taskset 0x15 command # Set the process's CPU's afinity to CPU 1, 2, 3 and 4

    01, 03, 07, and 15 are just decimal values of 0001, 0011, 0111, 1111

  • List all block devices (except RAM disks)


    This is useful to find the device path of your usb, sdcard, or hard drive. For example:

      NAME                  MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
      sda                     8:0    0 465,8G  0 disk
      ├─sda1                  8:1    0   487M  0 part /boot
      ├─sda2                  8:2    0     1K  0 part
      └─sda5                  8:5    0 465,3G  0 part
      ├─ubuntu--vg-root   252:0    0 457,4G  0 lvm  /
      └─ubuntu--vg-swap_1 252:1    0   7,9G  0 lvm  [SWAP]
      sdb                     8:16   1  14,6G  0 disk
      └─sdb1                  8:17   1  14,6G  0 part /media/usb
      sr0                    11:0    1  1024M  0 rom

    The device path of my usb’s first partition is /dev/sdb1

  • Mount a filesystem (i.e a usb drive, a hard drive…)

      sudo mount </device/path> </mount/point>


      sudo mkdir /media/usb
      sudo mount /dev/sdb1 /media/usb
  • Unmount a file system from a mount point

      umount </mount/point>

    Note: This only unmount the file system at the particular mount point, not all mount points that the file system is mounted to

  • Eject a device

      sudo eject </device/path>
  • Shutdown and restart

      sudo shutdown -P now # shutdown the machine
      sudo shutdown -r now # restart the machine

Tips and tricks

  • Use tree to visualize folder’s structure

      tree <path>

    For example:

      $ tree ./
      ├── docker-compose.yml
      ├── logs
      ├── nginx
      │   └── site.conf
      └── www
          └── index.php

    However, tree must be installed first

      sudo apt-get install tree -y
  • Use watch to execute a program periodically, then show the out put on the screen.

      watch -n <seconds> <command>

    For exampple: watch your memory usage every 5 seconds

      watch -n 5 free -m
  • Use htop to monitor your system resource usage


    htop must first be installed

      sudo apt-get install htop
  • Use tmux to multiplex your terminal

      sudo apt-get install tmux
  • Shorthand command to resume your tmux session when available, else start a new session

      alias "$TMUX_ALIAS"="(tmux has -t $TMUX_SESSION_NAME && tmux attach -t $TMUX_SESSION_NAME) || tmux new -s $TMUX_SESSION_NAME"

    Put the above script to your ~/.bashrc, then everytime you want to use tmux, you can just type tfox instead.

  • Connect to your tmux session when doing ssh. Start a new session if not available

      # Automatically start attach tmux session when under ssh
      if [ -n "$SSH_CLIENT" ] || [ -n "$SSH_TTY" ]; then
      if [[ "$TERM" != "screen" ]]; then
          (tmux has -t $TMUX_SESSION_NAME && tmux attach -t $TMUX_SESSION_NAME) || tmux new -s $TMUX_SESSION_NAME;
  • Add the following command as keyboard shortcut (Fox example, ScrollLock) to toggle fullscreen mode of the currently focused window

      wmctrl -r ":ACTIVE:" -b toggle,fullscreen