Huh?

The X Server is the part of a Linux operating environment that provides graphics. Once in a while it may lock up, usually due to bad drivers. Other times programs just happen to be taking up all memory, or other problems that you don’t want to wait for ever to resolve by themselves. A quick fix is to just kill X (which also kills graphical applications), and restart it. (You don’t have to restart it, even, in distributions that are set up that way. In Ubuntu, X starts up again automatically.)

OK, ever since the beginning the time or of Linux, or something like that, Ctrl+Alt+Backspace has been the key combination to kill X. Earlier, this year, though, somebody (who shall remain nameless to prevent the ire of countless old Linux hands) changed X.org (the X server most often used with Linux) to not respond to Ctrl+Alt+Backspace.

I thought that the reasoning behind the move was ridiculous. It had something to do with Windows users accidentally hitting Ctrl+Alt+Backspace (does anybody do that?) and with a conflict with some Emacs key combinations.

Here’s what one upset user said:

I will tell you that this argument about
confusion is totally bogus from an entire Linux community standpoint. The Emacs community is miniscule in size comparison to the overall Linux community. In over thirty years of working with *nix systems and thousands of users and machines not once has a user ever complained about confusion or problems involving the Ctrl-Alt-Backspace key combination. I am concerned because it appears that a tiny minority of Emac users have managed to lobby for a very significant change in default behavior for X server control to the detriment of the majority of users and administrators in the Linux community.

Disabling X’s DontZap to reenable Ctrl+Alt+Backspace

The response was that you can reenable Ctrl+Alt+Backspace by making an entry in /etc/xorg.conf, the X configuration file:

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

Well, OK, but the point was about the defaults. By default it would be handy to have Ctrl+Alt+Backspace already enabled so you can use it when you have a crash. Or when someone else does so you can tell them what to do about it.

Anyway, there’s one small problem: there’s no DontZap option anymore! They took that one away too!

Actually, they put the option into XKB (keyboard manager).

Reenable Ctrl+Alt+Backspace in GNOME/Ubuntu

In Ubuntu Karmic 9.10 (and probably other distributions running the GNOME desktop environment), it’s very easy to reenable Ctrl+Alt+Backspace. Just open the keyboard preferences dialog from the System: Preferences menu:

Ubuntu Karmic: Opening Keyboard Preferences

On the Layouts tab, hit Layout Options:

Ubuntu Karmic: Keyboard Preferences

This brings up the Keyboard Layout Options dialog.

Ubuntu Karmic: Keyboard Layout Options: Ctrl-Alt-Backspace

Open up the option for “Key sequence to kill the X server“. Check the box next to “Ctrl+Alt+Backspace”.

That’s it.

Reenable Ctrl+Alt+Backspace in KDE and the command line

You can do the same thing in KDE and the command line. See here for details:
https://wiki.ubuntu.com/X/Config/DontZap

Other ways to regain control without killing the X server

It’s much handier to have enabled this before a hang. But, if you haven’t, there are still a few options other than turning the computer on and off.

The first thing I often do if there’s a problem with X is to switch into a virtual console. That’s a text-based console where you can run a Bash shell. To do this press Ctrl+Alt+F1 (hold down Control, then also Alt, then also F1). Then you can log in with username and password.

From there, you can run top to find out the offending program. I usually run htop, which is a nicer and easier program list than top and kill the program from there or exit and run kill -9 or killall from the command line. For example, let’s say VLC is hogging memory. I’ll do:

killall vlc

This kills all vlc instances. This is often all that is required to return X back to normal, and so I don’t have kill X as well. After all, why use a cannon when a fly swatter will do?

Note: another key combination to be aware of is Alt+SysRq+R. This puts the keyboard into raw mode, meaning the hung X server won’t be processing key input. Then do Ctrl+Alt+F1. You’ll probably want to hold down the right Alt because the left one in combination with SysRq gives you a screenshot.

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