X display sharing fails (xauth)

[Bill Davidsen]

Joe Smith wrote:
> I often need to test gui applications under a different login, so I can 
> easily wipe out .dotfiles and run with a known environment. I've had 
> this working since F8 with an xauth entry that allowed the other user 
> access to my display. All I needed was a terminal window logged in as 
> the other user, and I could run apps that needed access to the X display.
> 
> A couple of days ago, this stopped working. Now, as the test user, I get
> 
> $ firefox
> No protocol specified
> Error: cannot open display: :0.0
> 
> and from my normal desktop login, I get
> 
> $ xauth list
> xauth:  error in locking authority file 
> /var/run/gdm/auth-cookie-XXGB42IU-for-jes
> 
> I can use "xhost +" but I'd prefer to be a little more specific, even 
> though I'm the only user.
> 
> Switching users through the panel "User Switcher" is not convenient: I 
> have to enter a password every time I switch users and I can't run 
> things side by side on the same display. I don't really need full 
> console access, just the display.
> 
> Any ideas what broke, or suggestions for getting my old configuration 
> working again?
> 
Several thoughts... first, since you don't tell us what you meant by "an xauth 
entry that allowed the other user access to my display," no one will see 
anything there. Second, did you do anything with networking and/or DNS which 
could have confused the issue? That includes installing "upgrades," which has 
been known to close security holes by making the whole method stop working.

And finally, why not just ssh to the other user with X forwarding?
	ssh -X user2 at localhost
would let user2 run X apps without xhost configuration.

Maybe some of that will help.

-- 
Bill Davidsen <davidsen at tmr.com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot