Introduction

• Linux is only a kernel (collection of drivers, task schedulers etc).
• Red Hat, Fedora, Ubuntu, Manjaro, Kali, NixOS etc. are OS distributions (uses the Linux kernel).
• Linux OSes can be used via CLI (suitable for servers) or GUI (suitable for personal laptops/desktops).
• Linux CLI
  • sh
  • bash
  • csh
  • ksh
  • zsh
  • fish
• Linux GUI:
  • Window Manager
    • X org (DE required)
    • Wayland (DE required)
    • bspwm
    • i3
    • i3-gaps
    • awesomewm
    • dwm
    • ...
  • Desktop Environment (All requires WM)
    • Gnome
    • KDE
    • Mate
    • Unity
    • xfce
    • ...
• Linux is multi-user (multiple users can login at the same time)
• "root" is the superuser

Commands

• cat to see the contents of a text file e.g. cat /etc/fstab
• nslookup to get the IP address from domain name or vice versa e.g. nslookup ip, nslookup domain
• ifconfig to get the IP addresses of my machine
• yum to install or update packages in RedHat (apt-get in Ubuntu, pacman in Arch etc.) e.g. yum update, yum install python, yum remove python
• ping to check if a server is online/responding (ICMP is blocked by AWS) e.g. ping ip, ping domain
• ssh to login into remote servers e.g. ssh -i keyfile username@ip, ssh username@domain
• scp to login into remote servers e.g. scp -i keyfile /source username@ip:/destination, scp /source username@domain:/destination
• cd to move into a directory e.g. cd /tmp
• mkdir to make directory e.g. mkdir dir
• ls to list files inside a directory e.g. ls, ls /tmp, ls -l
• pwd to get the present working directory e.g. pwd
• tracert to get the gateway IP addresses of the given destination address/domain e.g. traceroute google.com
• ip link show to get the network interfaces, mac addresses (active + inactive)
• ip route show to get the gateway addresses of the machine.
• mount to mount a filesystem (partition / shared filesystem etc.)
• umount to unmount a filesystem (partition / shared filesystem etc.) e.g. mount /dev/sda1 /mnt/directory
• fdisk see and update the attached disks and partitions e.g. fdisk -l, fdisk /dev/sda
• tree to get the directory tree
• which to get the location of the command e.g. which ls
• man manual for any command. e.g. man ls
• df -h list the mounted partitions
• su switch user
• whoami or id to see who I am logged in as
• systemctl start/stop/restart/reload/enable/disable to manage running services
• chmod to change file mode. e.g. chmod +x filename to give execute permission.
• mv to move or rename file or directory
• cp to copy file or directory
• rm to remove file or directory