How to set keyboard combination to kill the X server?

It used to be ctrl+alt+backspace to kill x server, but for some unknown reason, it was decided to disable that combination and use something else (I think it is right alt + printscreen +k).

So, how to enable ctrl+alt+backspace?

I have seen it can be done with installing dontzap, but I know there is a way to set that combination from system setup.

Gnome:

Open the keyboard preferences (Search for keyboard in Dash), go to the Layout tab and press Options. Open Key sequece to kill the X server and toggle Control + Alt + Backspace

KDE:

I don't run KDE so I can't verify it or make a pretty screenshot, but according to the Ubuntu Wiki, you do as follows:

• Open System Settings

KDE 4.1 - KDE 4.5

• Select "Regional & Language"

• Select "Keyboard Layout".

• Click on "Enable keyboard layouts" (in the Layout tab).

• Select the "Advanced" tab. Then select "Key sequence to kill the X server" and enable "Control + Alt + Backspace".

KDE 4.6+

• Select Input Devices under the heading Hardware

• Select Advanced Tab

• Click on Configure Keyboard Options

• Enable "Key sequence to kill the X server" and enable "Control + Alt + Backspace".

If you are looking for a solution which is independent of Gnome/KDE/Fluxbox or any Desktop Environment or Window Manager, try the following. This command is part of the X Window System.

From https://wiki.ubuntu.com/X/Config/DontZap#Using_the_command_line

Using the command line

You can type the following command to enable Zapping immediately.

setxkbmap -option terminate:ctrl_alt_bksp

If you're happy with the new behaviour you can add that command to your ~/.xinitrc in order to make the change permanent.

I have provided more information in my answer to 10.10 How can I enable Ctrl+Alt+Backspace?