RE: Info on "Can't open display"

[Suhaib Siddiqi <ssiddiqi at inspirepharm dot com>]

Chris
It is your VPN software.  Several other users had same problems.  You will
find 
more messages in mail archive.

Suhaib

> -----Original Message-----
> From: Christopher Landrieu [mailto:landrieu@hotmail.com] 
> Sent: Wednesday, June 06, 2001 1:50 PM
> To: huntharo@msu.edu
> Cc: cygwin-xfree@cygwin.com
> Subject: RE: Info on "Can't open display"
> 
> 
> Harold,
> 
> I appreciate your reply.
> 
> I originally considered that it could be an interaction with 
> VPN software 
> because I do have VPN packages on both computers, however the 
> problems occur 
> whether the VPN software is active or not.
> 
> As well, the problem is not with all programs making TCP/IP 
> connections to 
> port 6000 on the localhost.  That is evidenced by the fact 
> that the TeraTerm 
> SSH with X Forwarding worked.  X Forwarding works by having 
> the remote SSH 
> server set up a dummy X server on the remote machine (display 
> 10 - :10.0) 
> and setting the DISPLAY variable to remote-machine:10.0.  The 
> SSH server 
> then tunnels the X traffic through the encrypted SSH socket 
> to the SSH 
> client.  The SSH client opens a connection to the local X server 
> (localhost:0.0).  The SSH client redirects the tunneled X 
> traffic from the 
> SSH Socket to the connection to the local X server.
> 
> Therefore, TeraTermSSH is successfully making a working X 
> connection to 
> localhost:0.0.  TeraTermSSh in this case is technically an X 
> client.  The 
> only programs that fail to successfully connect are the local 
> X clients from 
> XFree86.
> 
> Also, the local X clients cannot even connect properly to a 
> remote X server. 
>   I believe that the TCP/IP connection is being established 
> successfully but 
> that these local X clients are not successfully setting up 
> the X11 protocol 
> connection.  This is because when I try to run "xterm -display 
> remote-x-server:0.0", I can see the connection openned on the 
> remote machine 
> ("netstat -np" as root on my linux box).  I believe the X 
> server is then 
> dropping the connection (like when I do the "telnet localhost 
> 6000" test).
> 
> That is why I would like to try and sniff the packets and see what 
> communication is taking place between the X server and the X clients.
> 
> I'll let you know what I find.
> 
> Chris
> 
> >From: "Harold Hunt" <huntharo@msu.edu>
> >To: <landrieu@hotmail.com>
> >Subject: RE: Info on "Can't open display"
> >Date: Wed, 6 Jun 2001 13:24:10 -0400
> >
> >Chris,
> >
> >Hopefully you can identify the exact conditions that cause 
> this, as we
> >haven't yet had a thorough examination of this problem.
> >
> >You might want to take a look at the current information we 
> have regarding
> >this problem, as answered in my draft FAQ:
> >http://www.msu.edu/~huntharo/xwin/docs/faq/cygwin-xfree-faq.h
tml#AEN290
>
>A couple users have reported that removing VPN or firewall software solved
>their problems.  It makes sense that VPN software would cause a problem, as
>VPN software usually causes connections to be redirected to a VPN tunnel;
>when a request for 127.0.0.1:6000 or host-name-or-ip-address:6000 shows up
>at the end of the VPN tunnel, the computer at the end of the VPN tunnel
>can't satisfy the request, so the connection fails.  (The VPN machine isn't
>running Cygwin/XFree86, so 127.0.0.1:6000 would fail; as for
>host-name-or-ip-address:6000, the VPN software may reject that because it 
>is
>looping the VPN back onto itself.)
>
>It would have to be pretty braindead VPN software that causes this problem,
>as 127.0.0.1 should never be redirected.  I used the included VPN support
>with Windows 2000, but I never had problems.  Users of lesser known VPN
>software seem to be the ones reporting problems :)
>
>Uninstalling VPN or firewalling software from a machine doesn't always fix
>the problem, as the uninstall program may leave certain files and settings
>in place, thus preserving the problem.
>
>Anyway, let me know what you come up with,
>
>Harold
>

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