Problem with X server

[Wiedemann, Shane CIV NAVAIR]

Success!!  You solved my problem! Thank you for taking time to
respond...much appreciated. 
Cheers,
Shane Wiedemann

-----Original Message-----
From: redhat-list-bounces at redhat.com
[mailto:redhat-list-bounces at redhat.com] On Behalf Of Nigel Wade
Sent: Tuesday, May 06, 2008 9:09
To: General Red Hat Linux discussion list
Subject: Re: Problem with X server

Wiedemann, Shane CIV NAVAIR wrote:
> So this problem is most likely user error; none the less...
> I have some software (only one other place has this software) that to 
> view video windows that the software tries to pop up, you need to use 
> the following command to get it to display:
> "software_name -display hostname", or at least that is what I am told.
> I have inserted my hostname where it says "hostname" and verified with

> "uname" that my hostname is correct.  I am not connecting to a remote 
> machine, am not on a network and am running the software on a 
> stand-alone machine.  The vendors of the software do connect remotely,

> I believe, and they can pop video display windows just fine.  Whenever

> I run the software, I get a message that says "Unable to connect to x 
> server".
> I currently have the DISPLAY variable set to ":0.0" and this seems to 
> be fine for opening programs, such as NEdit.  Any other setting (even
> "hostname:0.0") and I cannot start programs such as editors and other 
> programs that open in a separate window.  I get errors that say "can't

> open display" and the like.
> 
> When I run the software, if I leave out the command "-display
hostname"
> all video rendering is done behind the scenes, i.e., I can't view it.

> I have tried replacing "hostname" with all of the following:
> hostname:0.0
> :0.0
> hostname:0
> localhost
> localhost:0.0
> localhost:0
> 
> Any clues?

I think you probably need to enable your X display to listen on the
network.

The software you are using is pretty strange. It should not be necessary
to specify the -display option, it should use whatever DISPLAY is set
to. However, given that it does what it does, you are pretty much at its
mercy.

By default the X display does not listen for network (TCP) connections,
it allows local connections using a UNIX domain socket. If you have
DISPLAY set to :0 clients will connect on the UNIX socket, but if you
specify a hostname (even localhost) then the connection will be done on
a TCP socket. If the X server isn't listening on a TCP socket then the
connection will fail. This is a quite sensible security precaution (it
prevents any non-local clients connecting to your display, even if you
use the xhost + security disabler) but can cause problems for any
software which expects to be able to connect via a TCP socket.

To enable the TCP socket you need to modify the X server startup. How
you do that depends on what version of RedHat you are using. For RH 4 it
is set in /etc/X11/gdm/gdm.conf. To enable TCP connections you need to
change the line:
   DisallowTCP=true
to
   DisallowTCP=false

In KDE desktop you can also set this using the System Settings->Login
Screen dialog (I presume there's something similar for Gnome). In the
Security tab un-check the box marked "Always disallow TCP connections to
X server".


--
Nigel Wade, System Administrator, Space Plasma Physics Group,
             University of Leicester, Leicester, LE1 7RH, UK
E-mail :    nmw at ion.le.ac.uk
Phone :     +44 (0)116 2523548, Fax : +44 (0)116 2523555

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