if you are using gnome,  gnome-keyboard-properties may helps.
in the "Layouts" tab, there's a "Layout Options" button.
click it and  choose the "Control + Alt + Backspace" in "Key sequence to kill the X server"

it seems "setxkbmap -option terminate:ctrl_alt_bksp" helps, too.

ps: I'm new to this mailing-list and can not reply to former post


2009/10/27 Sebastian Beßler <webmaster@darkmetatron.de>
Am 27.10.2009 02:03, schrieb Dale:

> This is the sequence you tried I hope.  This is copied from a message
> sent to me a loong time ago.
>
> Hold down Atl, hold down SysRq, press each of the keys in turn. The usual
> full sequence is R-E-I-S-U-B

Yes, it is.
But after E there is only darkness and no response to any other SysRq
key. The ati-driver just don't want to be killed.

With the open drivers all works as it should with SysRq but I like
3D-acceleration and that is by now far away for my chipset with open
drivers.

Greetings

Sebastian