How to enable killing Xorg with Ctrl+Alt+Backspace

Modify /etc/X11/xorg.conf or a .conf file in /etc/X11/xorg.conf.d/ with the following. (note: it is ok if this is all you have in your xorg.conf as xorg will still auto-detect the rest (note: that is if auto-detect works for you without it))

Section "ServerFlags"
    Option "DontZap" "false"
EndSection

Section "InputClass"
    Identifier      "Keyboard Defaults"
    MatchIsKeyboard "yes"
    Option          "XkbOptions" "terminate:ctrl_alt_bksp"
EndSection

The DontZap feature is no longer working for me on Fedora 16 and Ubuntu 11.10 (most recent releases as of November 2011), so I found an alternative.

According to the X11R7.5 release notes, it appears that this functionality has been migrated to a XKB configuration option, therefore DontZap no longer works. I can't tell if this is a detail of the Xorg implementation in Fedora and Ubuntu, or if this affects other distros as well.

From http://www.x.org/archive/X11R7.5/doc/RELNOTES.txt

Terminate Server keystroke

The Xorg server has previously allowed users to exit the server by pressing the keys Control + Alt + Backspace. While this function is still enabled by default in this release, the keymap data usually used with Xorg, from the xkeyboard-config project, has been modified to not map that sequence by default, in order to reduce the chance that inexperienced users will accidentally destroy their work.

Users who wish to have this functionality available by default may enable it via the XKB configuration option “terminate:ctrl_alt_bksp”. For instance, the setxkbmap command can be used to enable this by running:

       setxkbmap -option "terminate:ctrl_alt_bksp"                       

Many desktop environments include XKB configuration options in their preferences to enable this as well.

In current Ubuntu releases, at least since 14.10, the keyboard-configuration package has an option to re-enable Zap:

$ sudo dpkg-reconfigure keyboard-configuration