Howto Enable Ctrl + Alt + BackSpace in Ubuntu Jaunty

By default Ctrl + Alt + BackSpace key combination in Ubuntu Jaunty was disabled.This shortcut key is used to restart X.

If you still want to use a key combination for restarting X you can use:

right alt + printscreen +k

Or, just to enable the old combination

# install this software
sudo apt-get install dontzap

# use this to enable the ctrl + alt + backspace
sudo dontzap --enable

#use this to disable ctrl + alt + backspace
sudo dontzap --disable

Source: http://www.ubuntugeek.com/howto-enable-ctrl-alt-backspace-in-ubuntu-jaunty.html