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This cheet cheet / general guide will explain what each command will do and when to use it. It's intended as a general guide/cheet cheet for linux beginners on the command line.

This Cheet Cheet assumes you use a Debian based system like Ubuntu but can be also applied to other Posix systems like MacOS and in some degree to non Posix systems like Windows. There are also definitions for each word that is not well know.

I would always recommend to watch those 2 Videos to get a core understanding of common Linux things:

https://youtu.be/LKCVKw9CzFo

https://youtu.be/42iQKuQodW4

To do:

  • Piping via | , >, >>
  • Grep
  • ls / ls -la
  • usermod
  • cd
  • man
  • cat
  • --help
  • ssh
  • pwd
  • rm
  • mkdir
  • touch
  • nano/ vim
  • cp
  • mv
  • kill
  • htop /top
  • ping
  • scp
  • info
  • history
  • clear
  • mount
  • ip a
  • permissions
  • external ip address throght things like ip.coolerwuffi.de or curl -4 icanhazip.com
  • curl
  • Bootloader, like grub or systemd-boot
  • wget
  • Common linux shortcuts
  • apt
  • systemctl/systemd
  • sudo

Definitions

Distro/ Distribution

A so called "Distro" short for Distribution could be intepreded as a sort of flavor/Versions of Linux. Popular Server Linux Distros are Debain, Ubuntu, RHEL (Redhat Enterprise Linux) and Alpine Linux

Repo/ Repository

Repository short "repo" is in general a place to store data, most common are git repositorys for code or package repositorys for Software

What is a .deb/.rpm?

Deb and Rpm files are softwarebundels that are used to install Software on their respective platforms. Debain based Distros use .deb files to install software while RHEL or SUSE based Distros use the .rpm format

Everything has an alternative

What you need to remember on Linux systems is that almost everything has an alternative way/software to do the same or similar jobs. This fragmentation has some standards and common software. Ex. The most common package manager to install software on Linux ist apt but there are also may alternatives out there like dnf, pacman, apk and so on. The most importened thing is to remember the core concepts. On the most common Distros most things are the same, GNU userspace, Systemd as a initsystem and so on

What is a Linux daemon?

A process which runs in the background and is not interactive. They have no controlling terminal on their own from the user's perspective from the desktop. They continue to exist and operate regardless of any user being logged into the server if the computer is on( See). On most Linux system you will use Systemd for that. '* On Windows there are Windows Services similar to Linux daemons

Use TAB were possible

The Tab key is mostly forgotten today but on the command line it is essential for easy fast navigation use it every were possible

Common Linux Tools explained

Sudo

Sudo is a program to execute a command as another user in most cases the root user. The root user is the admin of every Linux out there. So if we want to run a command with elevated privages we will use sudo. Common command that require given privalages are:

  • systemctl enable/disable/start/stop
  • apt install/remove/update/upgrade

Apt

Apt is a so called package manager. Those are used to install Software or Libarys form Package repo. Those are hosted by your Linux Distro maintainers but you can also install third party software via .deb files. Apt has many arguements the most common are search, install, update, upgrade, remove, list and show. Here is a list which does what:

  • search searches throught the package index for the given string
    • apt search firefox this would give you results of packages that have either firefox in their name or description
  • install installs the software that is in the repo or local
    • apt install firefox will install firefox from the repository
    • apt install ./firefox.deb This will install the local firefox file onto your system
  • update will update your repository index.
    • So that if there is a new version of a software on the repo your host knows what is the newest version of given software
    • use apt update
  • upgrade Updates your installed software including your system software
    • This will upgrade all the installed software to the newest version of given software, it's recommended to restart your host after an upgrade
    • use apt upgrade
  • remove will remove/uninstalls software from your system
    • very easy to use
    • apt remove <installed_software_here>
  • list list out the available software on your repo
    • mostly used in combination with grep and the --installed option to list the local installed packages
    • apt list --installed |grep firefox This would list out the installed packages and uses grep to search for packages that have "firefox" in their name
  • show shows you information about the package
    • shows information about the package, things like dependencys upsteams Webpage, maintainer, version and so on
    • apt show firefox

Systemd/Systemctl

Systemd is that so called init system that runs daemons or sockets on a given system while systemctl is the software interface to control Systemd. Systemd is for the user a way to run software consitenly in the background on a given host. Common things that run like that are web, printing and virtualization. The most importend systemctl commands are status, enable, disable, start, stop, restart and reload. With those you can contol the systemdaemons. status: Displays the status of a service + Example: systemctl status docker.

  • enable: Enables a service so that it is automatically started at system startup
    • Example: systemctl enable docker
  • disable: Disables a service so that it is no longer started automatically at system startup
    • Example: systemctl disable docker
  • start: Starts a service
    • Example: systemctl start docker
  • stop: Stops a service
    • Example: systemctl stop docker
  • restart: Restarts a service
    • Example: systemctl restart docker
  • reload: Reloads the configuration of a service
    • Example: systemctl reload docker.

File navigation & management

Under Linux and other other Unix like and other Systems you will use nearly the same commands to navigate your file tree and manage them. The most well known Unix like desktopsystems are Linux, Android, MacOS and FreeBSD many command. They are mostly follow the Posix Standard.

Core Concepts

So to understand the most common things, I will explain them now rather than later. In Linux you don't have a C: or D: drive like in Windows instead you have the / aka root directory. For more information about multiple drives see mount This directory holds all files and folders of your system. The most imported root directorys are:

  • /etc short for Editable Text Configuration
  • /home where the non root user files are located
  • /dev contains external devices like hard drives and other things
    • /dev/urandom contains a unlimited number of random data
    • /dev/null all data moved to or from there is empty
    • for more read see the dd section
  • /root is the home directory of the root user
  • /tmp is a temporarily directory that will clean itself after each reboot
  • /usr contains system wide non essential software and librarys
  • /sbin contains system essential software
  • /bin contains your software binarys

But there are also some relative path variables that you need to remember:

  • ~/ This wave character is representative for the home dir of the current user
    • in case of the root user /root/
  • ./ A single dot indicates the current working directory
  • ../ Two dots represent the parent directory of the current working directory
  • .ssh/ a dot before a directory indicates to the system that it is a hidden directory
  • if you don't specify a directory path but insted only Documents/test.txt your system will try to use a relative directory with that name: ./Documents/test.txt
    • This is really handy for fast navigation on the command line
  • you can use the * as a symbol to specify that every things is meant
    • if you want so select all files or directorys that start or end with start use *start or start*

Commands to Navigate your file tree

ls
  • ls short for list is the most common command to list existing files and directorys that are inside of a given directory
    • ls -a will show you all directorys/files including hidden ones
    • ls -l will show the contend in a list format
    • ls arguments can be combined
      • like ls -la to show all contents of a file in a list format
    • in Windows you would use traditionally the dir command for that
pwd
  • pwd will print out the current working directory
cd
  • cd to "change the directory"
    • if you run cd without a directory it will go to the home dir of your user like cd ~/
    • can be used with relative paths (usually way faster)
      • likecd ./.ssh or cd ~/.ssh instead of cd /home/testuser/.ssh
    • cd !! to go back to the previous directory

Modifying content

touch

touchwill create a empty file

  • touch example.txt
mkdir

mkdir will create a empty directory

  • mkdir ~/
Edit files using an text editor of choice ex. nano or vim
rm

rm to remove files or/and directorys

  • use rm -r to remove directorys
  • be EXTEMLY CAREFULL with rm it removes ALL FILES and they GONE no trash dir just gone
  • never ever run rm -rf / it will stop your system form working and removes all other files
  • used like: rm testfile.txt or rm -r ./testdir
cat

cat will print out the contend of a given file

  • used like : cat testfile.txt

Piping, Redirecting and Shellscripting

On the most Linux systems the default shell ist "bash" on some other it is "zsh". On MacOS is "zsh" the default shell. The post imported thing is that they are Poisx complaint.

Piping

On the command line you can chain commands together like following example:

cat testfile.txt |grep test

In this example we are using cat to print out the contend of the testfile. That contend is piped via the pipe symbol | to grep. Grep will search for a given string in our case test. So if a line in the testfile.txt has the string test in it grep will print out the lines with the given string in it

Redirecting

There is also another symbol used on the command line with the "output redirection operator" > you can redirect the output to a file

apt list --installed > installedpackages.txt

Here we are listing the installed packages via apt and then redirecting the output to the "installedpackages.txt"

If we would repeat that command it will overwrite the existing file but if we want to append it to the file we can use the redirection symbol twiste >>

echo "hi, this is a test" >> installedpackages.txt
Scripting

If your want to combined commands you can write a shell script for that. You can use a graphical text editor like vscode or you could use a terminal text editor like nano or vim

#!/bin/bash

apt list --installed > installedpackages.txt

# This  will check via grepp if Firefox is in the installedpackages list
if ! grep -q "firefox" installedpackages.txt; then
    echo "Firefox is not installed. Installing..."
    sudo apt install -y firefox 
else
    echo "Firefox is already installed :D"
fi

Nano

Nano is a simple editor nice for quick edits but hides a lot of it's features behind config files. To use nano run nano testfile.txt if the file already exists it will load up the file. If not nano will create a new file If you fished your edit press ctrl + o to save the file and then press ctrl + x to exit nano

Vi/Vim/Nvim

Vi, Vim and Nvim are all text editors that build upon another. I would always recommend to use at least vim, because of it's text highlighting. The biggest upgrade to Nvim in my opinion is the build in file explorer which is really handy. They are not really easy for beginners cause the mode editor model isn't the norm nowadays and you have to remember some shortcuts. The most important is Esc to go back into Normal mode, then press : and then q!. This will force quit vim without saving.

Those are all mode based editors. You have 3 distinct modes, Normal, Insert and Visual.

  • You can enter Normal mode via the Esc key it's the default mode
  • To enter Insert mode press the I key, know you can write/edit your files
    • press Esc to return to normal mode
  • To enter Visual mode press the V key, know you can mark your text and copy it to your clipboard with Y, with P you can past your clipboard content into the editor
    • press Esc to return to normal mode If your are done with your edit go back to normal mode, then press : and then wq to save and quit

some useful shortcuts:

  • Normal mode: press U to go back to the change before
  • Normal mode: press cont + R to go forward to the newest change
  • Normal mode: press / then type in a string to search for given string thought the file
  • Nvim only Normal mode: press : and then E and Enter and the builtin file explorer opens it's self

ps/top/htop

WIP (Work in Progress)

dd

WIP

Neofetch/fastfetch

Neofetch and Fastfetch are tools to get information about your host system, which can be very import. They are both compatible with the same config but fastfetch is faster and still maintained. But it's not in every repo yet so Neofetch is there the way to go

jp:~/ $ neofetch
        ,'''''.      
       |   ,.  |    D E V E L C O O K I N G 
       |  |  '_'    _____________________ 
  ,....|  |..       OS: Fedora Linux 40 (GNOME Edition) 
.'  ,_;|   ..'      Kernel: 6.11.1-200.fsync.fc40.x86_64 
|  |   |  |         Uptime: 4 hours, 51 mins 
|  ',_,'  |         Packages: 3007 (dnf) 
   '''''            DE: GNOME 46.5 (wayland) 
                    Terminal: gnome-terminal 
                    CPU: AMD Ryzen 7 5800X (16) @ 4.851GHz [44.1°on] 
                    GPU: AMD ATI RX 5700 XT RAW II 
                    Memory: 6139.79 MiB / 31980.52 MiB 
                    Song: Unknown Artist - Unknown Album - Unknown Song 
                    ▂▂ ▂▂ ▂▂ ▂▂ ▂▂ ▂▂ ▂▂ 
                    _____________________

Grep

Grep is a basic but very blessing tool on linux with it you can search throught really anything (which is text based). Its most common used in combination with Piping, Redirecting and Shellscripting.

It can be used with "basic Syntax like:

apt list --installed |grep vpn

This would show you all installed packages with the "vpn" in the name.

with the -E flag standing for Extended Regular Expressions grep can search for a ERE for a definition see here

grep '^linux' file.txt

for more examples see

ssh

SSH is a remote tool to connect and administrate a bunch of systems. You can compare it to products like Teamviewer or Microsofts Remote deskop app. We will go over the base model of ssh first.

This articel from digial ocean is a great learning ground

ssh client server model

So to connect to a ssh server you will need a ssh server and a ssh client. A popular ssh server is the OpenSSH-Server or the Windows-SSH Server. Popular clients are the OpenSSH-Clients available on every OS. Another popular SSH client is Putty on windows.

SSH server config

SSH is a daemon service which can be controled via systemctl. You could restart ssh for ex. with

systemctl restart ssh

We will here only mension Linux's OpenSSH server. On a default server you will have a ssh server preinstalled. In /etc/ssh/sshd_config you can configure globle settings for your ssh server like the port which the server will be accessible in the future. Another big talking point is root access on a server. A direct root access should be disabled accept you are only using a ssh keypair. A keypair is like a key and a doorlock. Only a key can open the door. If you use ssh-keygen you will have a private and public key. A private key should be allways keept private. Nobody else exapt you should have access to your private ssh key. The public key is to be placed on your server we will later get to this.

Setup ssh on the client and server for a safe connection

Please make sure to have genereate a ssh keypair via ssh-keygen, it works on win terminal, linux and MacOS. If you done that you will have two new files in you $HOME/.ssh/ directory. Here we can use cat to cat out the .pub key. You can copy it to your clipboard.

If you are connected to a ssh server you will go into the Home directory of the user you want to connect as. In case of the root user /root otherwise /home/$USERNAME. You have to create now probaly a dir called .ssh mkdir .ssh. In there we now create a file called "authorized_keys". We will now edit it via our text editor of choice. You will now paste you public key into there. It should be oneliner. If it all worked, you can test the connection via

ssh <EDIT_USERNAME>@<IP_ADDRESS_OF_YOUR SERVER>

. If you dont know the ip address of you server you can use ip a to show that to you.

scp

WIP

ping

WIP

mount

WIP

Nice to know software

  • lynx/links
  • browsh
  • wireguard
  • nmap
  • rsync
  • gnu shreed
  • Networkmanager/ systemd-network / Netplan
  • nm-tui

In Action

In Case you want to install software for ex. Firefox

sudo apt install firefox

If you use this command you will elevate your privileges with sudo to the root (admin) user and execute apt with those privileges to install firefox on your system

systemctl enable --now docker

With this command you would enable docker as a [Systemdaemon](# What is a linux daemon) persistently and now on the running system, so you don't have to enable docker and start it now manually.