How to implement alternate zap key idea (was: Re: Poll: Should Xorg change from using Ctrl+Alt+Backspace to?something harder for users to press by accident?)

Peter Hutterer peter.hutterer at
Mon Sep 22 22:03:35 PDT 2008

On Tue, Sep 23, 2008 at 04:39:49AM +0000, Jason Spiro wrote:
> Thanks for the info.  1. So I guess when using evdev, a way to implement my
> Ctrl+Alt+Bksp then Ctrl+Alt+Y idea would be this?:  Ctrl+Alt+Bksp should latch
> some new modifier called ctrl_alt_bksp_was_pressed, and Ctrl+Alt+Y should zap X
> only when that modifier is latched.  Would that work?

maybe. You'd need to look at XKB's compat capabilities there.

Anyway - that's taking the hard way out. 
your claim was that CAB is too easy to hit. So disable it - it could be easily
done at runtime through xkb options. Or put it on ctrl-alt-shift-F12 or

Alternatively, have a client listen to CAB, load the normal xkb behaviour, pop
up a dialog "if you want to kill the server, hit CAB now". (this is just idle

> As for the Ctrl+K+X idea (which I don't know is as safe; 

AFAIK, XKB will only handle combinations with modifiers. sequential key combos
must be done in a client.

> 2. is it possible that a heavy pet sitting on the keyboard and depressing all keys at once could cause
> X to think Ctrl+K+X was pressed?), 

yes. and those users with a pet octopus better choose a 9-key combo. Ha, 
serves them octopodiformes right for having 2 fingers less than us!

There is a thing such as cost/effort. stop your pet sitting on the keyboard,
or disable zap.

> 3. are kbd and evdev each able to detect such a key combination? 

both are designed to handle key events - yes.

> 4. Are the majority of PS/2 and USB keyboards able to transmit such three-key combos reliably?  

they are designed to handle keyboard entry - yes.

> 5. Do most users know how to press multi-letter key combinations?

Depends on your definition of "most" and of "users". I know a fair few that
would go looking for a post box when you start talking about multi-letter


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