$DISPLAY variable empty after SSHing

Tue Aug 4 15:55:00 GMT 2009

On 04/08/2009 05:27, Andrew DeFaria wrote:
> mcoughlin wrote:
>> Well it is good to know that it is doable.
>>>> My computer is running Windows Vista, the middle computer runs Red Hat
>> 3, and the work computer runs Red Hat 4.
>>>>>> ssh -X computer #2
>>>>>>>> Warning: untrusted X11 forwarding setup failed: xauth key data not
>>>> generated
>>>> Warning: No xauth data; using fake authentication data for X11
>>>> forwarding.
> These warnings are significant. Why don't you resolve them first then
> see if the problem persists.

I doubt very much that these warnings are significant.
The OP says he tried with ssh -Y (which is the way to 'resolve' these 
warnings), as well as ssh -X.
Not having X11 forwarding on the server as suggested elsewhere seems a far 
more likely cause. Adding '-v' to the ssh command line is usually helpful in 
debugging ssh problems.
> Note I have not totally figured out what causes this and what the proper
> solution is. It does involve using xauth and adding the proper auth key.
> My internet research on this has yielded hazy results. I also noticed
> that this tends to happen when you are not yourself. By that I mean that
> I've seen this happen when I su as somebody else then do an ssh to
> another machine. IOW somethings screwy in the authentication of the user
> thuse ssh/X considers it unsafe and perhaps is not passing along the
> proper DISPLAY because of this.

A very clear explanation can be found in point 3 in this email [1]
This is pointed to by the Cygwin/X FAQ and these issues discussed there, 
although I agree the language there could use some clarifications.
[1] http://cygwin.com/ml/cygwin-xfree/2008-11/msg00154.html
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