XDMCP Configuration

XDMCP is the last protocol a terminal uses during the boot process. Thus, it is likely a good idea to configure this protocol after the others are already working. If your terminal can boot, but stops at a gray screen with an 'X' for a mouse pointer, then this is the only protocol between you and a working terminal! Configuring XDMCP is not the same on all servers - it depends on what Display Manager (DM) you are using on your server. Note, this is not necessarily determined by what Desktop Environment (DE) you are using.

If you are able to login to your server and run X from a local console, then you have a properly working DM, and can use this guide to configure it. Examples of display managers include XDM, GDM and KDM. XDM is the old standard display manager that is included with the Xwindows distribution. GDM is the Gnome Display Manager, and KDM is the KDE Display Manager. To determine which you have running on your server, issue the following command:

  # ps -e | grep "\ .dm"

 6854 ?        00:00:00 gdm

Note that in the above example I am using GDM as the display manager (DM).

Configuring your DM

Choose which DM you are using, to see instructions on how to enable XDMCP

• XDM Config - Older XDM display manager
• KDM Config - KDE Dispay Manager
• GDM Config - Gnome Display Manager
• Again, your DE might not match your DM. Example: You can use GDM, and still login to KDE!

• There is an attachment below called remoteX.sh that has been tested with RHEL 4 and provides a menu driven interface to the above. -- MohammedArafa - 09 Mar 2006

Verify XDMCP is available

To verify your DM is listening to XDMCP requests, use the following command:

  # netstat -apn | grep ":177 "

You should see a line like this returned:

   udp      0    0 0.0.0.0:177           0.0.0.0:*                    5958/gdm

If XDMCP is not available for your DM, restart it with the following command:

  # /etc/init.d/xdm restart

WARNING: Restarting your DM, will kill all X sessions on your server, including local and remote. If you are logged into your server with X, be sure to logoff, then use a console terminal (<Ctrl>-<Alt>-<F1>) or SSH to run the above command!

Once XDMCP is available on your server, any terminals that are already booted to a gray screen should (within a couple minutes) suddenly display a login screen. Optionally, you can reboot the terminal to test your configuration completely.

For further troubleshooting help, you can view the more detailed Gray Screen troubleshooting guide.

-- SteveSwitzer - 07 Dec 2004

Once you have XDMCP enabled, you can also access terminal sessions from Windows computers using XWindowsServersForMicrosoftWindows