====== How to kill programs (and possibly their children) ======

===== kill =====
Sends a signal to a process.

===== pkill =====
Kills a process based on its name.

===== killall =====
Kills all processes with the name(s) specified as option(s).

===== xkill =====
  * kills GUI programs in X11
  * click a window with left mouse to kill its process
  * exit it with Esc or right-click