Quick X window problem

[Simon Andrews]

Neil Marjoram wrote:
> Sorry to be a bit thick, I could find the answer anywhere. 
> 
> I am trying to display an X app from a different system on my system. It
> does not seem to work on FC2, has anything changed?
 >
> Remote :
> export DISPLAY=hostname.here.uk:0.0
> 
> Local :
> xhost +
> access control disabled, clients can connect from any host
> 
> Remote :
> ./firefox &
> 
> (firefox-bin:28349): Gtk-WARNING **: cannot open display:
> 
> Is there anything else that controls the security for X now? Or am I
> being a little thick?

A couple of things.

Is the X server on the remote machine accepting remote connections?  Try 
doing a ps -ef | grep X and see what you get.

# ps -ef | grep X
root      1963  1952  0 Jul07 ?        01:07:59 /usr/X11R6/bin/X :0 
-audit 0 -auth /var/gdm/:0.Xauth -nolisten tcp vt7

If the X server was launched with the -nolisten flag then it will only 
accept connections from localhost (or those tunnelled to localhost via 
ssh).  If you're using FC2 on the remote machine then this flag is added 
automatically by gdm as a security measure.  To remove it you need to 
edit /etc/X11/gdm/gdm.conf.  Alter the line which says:

#DisallowTCP=true

so that it reads:

DisallowTCP=false

and then restart X (killall X).  You should now be able to make remote 
connections.

The other thing which could be stopping the X connections would be a 
firewall on either of the machines.  /etc/services says X needs 6000/tcp 
to be open, but there may be other ports required too, try temporarily 
disabling your firewall and see if that lets anything through.

As has been suggested before though, the easiest way around this is just 
to use ssh, where you can get secure X tunnelling for free!

Hope this helps

Simon.