Linux newbie question: problems using XDMCP to remotely start KDE session from a Windows PC

Nigel Wade nmw at ion.le.ac.uk
Wed Nov 30 12:54:41 UTC 2005


Jason M. Dolinger wrote:
> Hi all,
> 
> I am brand new to the Unix/Linux world, just started taking the plunge.  
> First of all, please forgive me if this is not the appropriate place to 
> ask such questions...
> 
> I just installed Fedora Core 4 and have been playing around with it for 
> several weeks now.  I also have a Windows XP machine connected to the 
> same router as the linux box.  I'd love to be able to do everything from 
> one machine, therefore setting up an X server on the windows box to run 
> X programs and have them appear on my windows machine.  I downloaded 
> Xwin32 and have been able to do what I just described.
> 
> However I'd like to take it to the next level and be able to popup the 
> entire KDE desktop on my windows machine.  I believe that the way to do 
> this is using XDMCP, and then Xwin32 is only remotely managing the KDE 
> session running on the Linux PC.  However, upon trying to use the XDMCP 
> option in Xwin32 to connect, my entire Windows desktop turns grey, with 
> a slightly linux-y looking mouse pointer, but nothing ever happens.  I 
> need to Alt-tab to get back to any of my other windows programs.  Has 
> anyone ever seen this before?
> 
> A few things:
> 
> 1.  In the KDE Login settings (I believe that runs gdmsetup), I've 
> checked  "Enable XDMCP" on the XDMCP tab (I'm using the SAMS Red Hat 
> Fedora 4 book and it led me to believe that this is all I would need to 
> do).

Are you sure? I don't have a Fedora 4 setup to hand at the moment. But the 
default in RHEL 4 is to use gdm, and this is controlled by 
/etc/X11/gdm/gdm.conf. Check which display manager is actually running.

Also, to see if your display manager is accepting connections from the network 
do a 'netstat -l' and see if there is a udp server listening on *:177 or *:xdmcp.

> 2.  I've edited /etc/X11/xdm/xdm-config to comment out the line 
> "DisplayManager.requestPort:   0".  I added a "!" in front of that line.
> 3.  I've edited /etc/X11/xdm/kdmrc to change the line "Enable=false" to 
> "Enable=true" under [Xdmcp].  Both this step and step 2 I found from 
> various internet postings and thought I'd give them a try.
> 4.  On my network, my windows PC gets a dynamic IP address from my 
> router and I configured the Linux machine to use a static IP.  I've set 
> up Xwin32 to connect to Linux using it's IPaddress, and the Xwin32 
> configuration specifies the IP address of the windows machine to route 
> its display back to.  Both machines can only ping each other using their 
> IPaddresses, not hostnames (I've nothing set up in the host files for 
> either machine).

How is the X server started? Does it broadcast, or query the XDMCP server?
It's strange that the X server would need to be configured with its own IP number.

> 
> Between each configuration steps 1, 2 and 3, I restarted the Linux 
> machine (the postings mentioned restarting just X, but I didn't know how 
> to do that.  They actually mentioned restarting the X server, but that 
> didn't make sense to me.  Isn't the Xserver what is running on my 
> Windows PC, but I made the changes on the Linux side?  I thought I would 
> need to restart whatever is running on the Linux side, is that referred 
> to as the X client?).

In these situations the idea of server and client gets somewhat blurred. What 
actually needs restarting is the XDMCP server on the Linux box. This is, in 
fact, the X server on the Linux box, which communicates with the X server on 
your Windows box. During XDMCP the X server on your Windows PC is acting as a 
client to the XDMCP server (X server) on the Linux box. After login the XDMCP 
server is no longer in the loop, and the X clients on the Linux box communicate 
directly with the X server on the PC. Confused? You will be.

> 
> Well, that's really it.  Have I missed a magic step somewhere along the 
> line, or is the problem more complicated, related to my 
> hardware/firewall setup perhaps (I tried this while disabling my Windows 
> firewall, no luck)?  At this point, I'm not really sure if the issue is 
> the Linux configuration, my network or the X server configuration on my 
> PC.  Maybe a different X server (CygwinX perhaps?) would give me better 
> luck?
> 
> Sorry if this is such a basic thing, I really am just barely starting to 
> figure this thing out.
> 
> Thanks, any help would be appreciated!
> 
> Jason
> 
> 

The Windows firewall must permit the X11 port for connections. This is normally 
port 6000 for display number 0, and increments by 1 for each display.

Do you run a firewall on the Linux box? XDMCP requires port 177. You might also 
need to enable the font server (xfs) to listen on the network rather than just 
the UNIX domain socket (/usr/X11R6/lib/X11/fs/config), and also open that up 
through the firewall on port 7100.

-- 
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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