Introduzione
In questa guidà verranno illustrati vari modi per abilitare la combinazione di tasti Ctrl + Alt + Backspace molto utile per effettuare un veloce arresto di sessione.
Ubuntu «Karmic Koala» 9.10 o maggiore
In GNOME
0. Selezionare Sistema -> Preferenze -> Tastiera
0. Selezionare la scheda Disposizioni e fare clic su Opzioni disposizione
0. Fare clic su Sequenza di tasti per terminare il server X e abilitare l'opzione 'Control + Alt + Backspace
In KDE
* Launch "systemsettings"
* 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".
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.
Using HAL
You can add the following line in /usr/share/hal/fdi/policy/10osvendor/10-x11-input.fdi (inside the <match key="info.capabilities" contains="input.keys"> section):
<merge key="input.xkb.options" type="string">terminate:ctrl_alt_bksp</merge>
Ubuntu Jaunty 9.04
The DontZap option in the /etc/X11/xorg.conf file enables or disables the CTRL-ALT-BACKSPACE shortcut to restart the X-server. In previous Ubuntu releases, this shortcut was enabled by default, however this will change starting with 9.04 "Jaunty", as a number of users have complained about accidentally restarting their X-Server.
You can re-enable this shortcut by editing your /etc/X11/xorg.conf,
sudo nano /etc/X11/xorg.conf
then type your password, press enter, and use the simple text editor to add a ServerFlags section like this to the start, end, or middle of the file:
Section "ServerFlags"
Option "DontZap" "false"
EndSectionAnd then restart the Computer (or log out and back in) to apply the changes. The shortcut should be re-enabled now.
If you want to disable the shortcut, either delete the section (in Jaunty) or change it to this:
Section "ServerFlags"
Option "DontZap" "true"
EndSectionAnd then restart the Computer (or log out and back in) to apply the changes. The shortcut should be disabled now.
Aside: sticky keys
It may be worth mentioning that the Accessibility shortcuts (for both KDE and Gnome) are enabled by holding the shift-key for 8 seconds. (This is easy to do if, say, selecting multiple items with the mouse). As a result, it's easy to inadvertently enable "Sticky Keys". Now, if you press Ctrl and then release it, and a bit later, you press Alt-Bksp (the shortcut to delete a whole word), then Boom! Bye-bye X-session 
Also, unlike Ctrl-Alt-Del, the Ctrl-Alt-Bksp shortcut is not trapped. It's instant death (without confirmation) for the X-server, and too bad about your unsaved files. That's why DontZap is a good default.
For anyone missing the ability to kill the X-server in emergency, may I point out Alt-SysRq-R, followed by Ctrl-Alt-F1 (the first puts the keyboard back into Raw mode, i.e. outside the control of the X-server; the latter switches Virtual Terminal.) Or you can use Alt-SysRq-K to kill the current session.
