Ctrl+Alt+Backspace combination no longer works for restarting X server :

Maintainers say that they implemented this idea to prevent users from accidentally pressing this key combination (Ctrl+Alt+Backspace) which restarted the X server in previous releases by default. I cant imaging how someone can press this combination by mistake. Sometime X server may become unresponsive due to some applications hogging down the memory or using hard disk drive continuously and you no longer use the desktop. In that case restarting X server should be the ultimate solution. Yesterday this happened to my laptop and I could restart X server with this key combination, so yes enabling this option might be useful for some users.

To enable Ctrl+Alt+Backspace method to restart X server install the program dontzap. It is a python script and is used to set – Option “DontZap” “false” in the xorg.conf file. Install it with,

sudo aptitude install dontzap

To enable X server restart, type in terminal

sudo dontzap –disable

and to disable restarting X by above key combination,

sudo dontzap –enable

You no longer need the program after setting the options. Uninstall it with,

sudo aptitude remove dontzap

There is an alternate way to enable restarting of X server if you don’t want to install the program dontzap( its very tiny by the way) .You have to edit xorg.conf file manually.  Type in terminal “sudo gedit /etc/X11/xorg.conf” (without the quotes) and enter the password. Add following lines at the end of file,

Section “ServerFlags”
Option  “DontZap” “false”

and close the file. You need to re-login or restart the machine before this change takes place.