Starting a Remote X session using XDMCP

This thread is motivated by the thread X bug? When using XDMCP the login works but desktop is never shown but I believe a different focus.

I have two SUSE 11.4(x86_64) KDE 4.7.2 machines, I’ll call SUSE1 and SUSE2.
SUSE1 is my “local” machine, SUSE2 is my HTPC on the network, XDMCP is enabled.

Prior to KDE 4.7, I used Start a new Session on SUSE1 to get a new greeter screen and chose remote login from there, but there appears to be a bug and that method fails(I have entered KDE bug after seeing similar reports from other distros).

In the above Forum thread, I see the following comment:

Actually, the easiest way to check if/how the XDMCP server is responding is to do an X query to it:

X -query <server>

It should start an X session.

Depending on the server configuration, you might have to specify from which client:

X -query <server> -from <client> 

Use hostnames or ips for server and client.

I tried that from a Konsole window and also from CLI in VT2 (CTL-ALT F2) and get a similar message:

carl@SUSE1:~> X -query SUSE2

Fatal server error:
Server is already active for display 0
        If this server is no longer running, remove /tmp/.X0-lock
        and start again.

Must SUSE2 be at level 3 for this to work?
In this test, Konsole is running on SUSE1:0 and I am logged in on SUSE2:0 via a local keyboard.
I also have xvncserver running on SUSE2:1.
vncviewer works on SUSE1, but seems to bog down other applications.

Is the error message above complaining about SUSE1:0 or SUSE2:0 ?

I am trying to configure XDMCP as well, same configuration.

I had your problem and I fixed it by setting in gdm.conf DisplaysPerHost=2 and MaxRemoteSessions=16

Look at this pages:
GDM and XDMCP configuration for remote graphical Linux desktop access

However, my problem is that GDM is not starting from the client side. Instead Xnest or X -query only shows a black screen and I can not login.

I can also open individual windows through “ssh -X <host> xclock”, but not all are able to open, and is not the same. I would like to have the full login window.