[Nottingham] VNC black screen (XDM declaring seesion dead)

Michael Quaintance penfoldq at penfoldq.co.uk
Mon Jan 19 22:42:28 UTC 2009

Hi guys

I know I'm not in Nottingham anymore but I'm hoping someone here can 
still hit me with a clue stick.

I'm trying to set up VNC servers so we can persist our xterms when we 
take our laptops home and connect to the work VPN to continue where we 
left off.

I've got a server with RHEL (4 or 5, not sure which) and I've set up 
some VNC sessions the RedHat way using 


and then 

service vncserver start

This works, but if anyone wants to change their resolution, color depth, 
add a new screen or remove a screen, all the screens have to be killed 
and restarted. This is no use.

So I'm trying it the command-line way. I start a server using 

vncserver -query <machinename> <other options like geometry>

This gives me a new screen and I can connect to it and use it fine for 
the first two minutes.

After 2 minutes (DNS resolver timeout maybe??) the VNC log file gets an 

XDM: too many retransmissions, declaring session dead

The vnc session then goes black, I still have a cursor that responds but 
no windowmanager.

I'm not even using xdm. The box is configured for gdm but I'm not using 
that either. The vnc xstartup is calling twm by default (which is fine 
for our purpose.

Any ideas why xdm is declaring the session dead? Why does xdm care? How 
can I stop it caring?

The sessions started the RedHat way are still running fine. If I change 
the vnc xstartup to use gnome, the same 2 minute limit is seen.


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