Often when developing with psychotoolbox or psychopy/opensesame your program crashes. And I often then have a full-screen window open and cannot click somewhere else. I then try to Alt+Tab and execute “sca” (screen close all) into the matlab console, with often mixed success. Sometimes restarting the computer is the last option. Instead of restarting, a useful command in older ubuntu versions was: STRG + ALT + Backspace => restart X server (=> restart GUI).
In order to activate this again use:
setxkbmap -option terminate:ctrl_alt_bksp
PS: I wrote this blogpost because I looked up this thing multiple times – now I know where to look 😉