Key sequence to kill the X server (Control + Alt + Backspace)
Current default for X servers as shipped in various distributions is to not enable the traditional Ctrl-Alt-Backspace key combination to kill the X server. If you would like to re-enable this feature, you may do so in your desktop's Keyboard Preferences application. You may also enable it for the current session using the command
"setxkbmap -option terminate:ctrl_alt_bksp".