By default Ctrl + Alt + BackSpace key combination in Ubuntu Jaunty was disabled.This shortcut key is used  to restart X.This tutorial will explain how to enable this key combunation.

Install the “dontzap” package using the following command

sudo apt-get install dontzap

Open Terminal and type

sudo dontzap --enable

or

sudo dontzap --disable

Where “disable” means that Ctrl+Alt+Backspace restarts the xserver while “enable” means that it won’t.

Update :- Some more solutions from our readers

1)You don’t need to install software to enable it. Simply add the following lines to your xorg.conf file, making sure that when you paste it, it is NOT using smart quotes.

sudo gksudo gedit /etc/X11/xorg.conf

Section “ServerFlags”
Option “DontZap” “false”
EndSection

2) you can use

right alt + printscreen +k

to do the same effect