Do these on the Host Machine
1) Four files in /etc/X11/xdm/ need to modify: xdm-config, Xresources, Xaccess, and Xservers.
2) In xdm-config, DisplayManager.reque stPort is either commented out or set to the default (XDMCP) port, which is 177.
3) Xresources can be changed to value of your option. If you dont want to change leave it alone.
4) Xaccess file is how xdm determines access to the various hosts. The idea is that we want xdm to do two things. First, we want every host on the LAN to be allowed to choose from amongst all available X servers running on all other hosts. Second, we want to allow any host to be allowed to login to the current host as well as all the others. For the first, we make sure the following line is added to the Xaccess file:
* CHOOSER BROADCAST # xdm allows all hosts to ask for a list of available hosts
For the second, we add the following line to the Xaccess file:
* # xdm allows all hosts to login to this host
5) The final configuration change is to the Xservers file. Here, we do not want xdm to automatically start/use the local host's X server. If it does, it only allows us to login to the local host, whereas we want to choose which host we will use to login. Therefore, we comment out any local X servers configured in the Xservers file. If you have any X terminals or machines acting as dedicated X terminals, do not comment out those lines or the X terminals will not work.
6 If you want xdm to be run during all the runlevels that allow active network connections (usually 2-5). do this Add a line similar to the following to /etc/inittab:
xd:2345:respawn:/usr /X11R6/bin/xdm -nodaemon
Now we need to configure the Server
1) Now we decide if we want to start the X server manually from the command line, or have it started automatically for us at system boot. If we want to start it manually, we can either start the X server itself, or via the startx or xinit programs. We will do the former. Assuming Server name ullas :
X -indirect ullas
This starts the X server and has it send a query for any hosts that the xdm running on ullas finds available on the LAN. Xdm then responds with a list of hosts to choose for logging in. Starting the X server upon system startup only takes a little more work than doing so from the command line. On storch , a SYSV machine, the easiest way is to add a line to /etc/inittab as follows:
xs:5:respawn:/usr/X1 1R6/bin/X -indirect ullas
We also need to change the line that sets the default runlevel as follows (remembering that on this particular Unix implementation runlevel 5 is for a X windows environment upon startup).
That is it