Keyboard
sudo setxkbmap be : Set a keyboard to "Belgian" layout
Internet/network
pppoeconf : Configure PPPoE DSL internet connection
sudo ifdown -a : Put network interfaces down
sudo ifup -a : Put network interfaces up:
Troubleshooting
top : See what processes are running and how much memory or processing power they reserve.
killall firefox : Stop any program, in this case Firefox, but you can put any name of a running program after killall to stop it.
Pressing Ctrl+Alt+F1 takes you to a terminal only window, where you can run top or execute the killall program-name command. Ctrl+Alt+F7 takes you back to the window you were working in.
Bash scripting