Configuring GDM

GDM uses an entirely unique configuration system. The GDM configuration files usually reside in /etc/X11/gdm, so check that directory first. If you can't find the files there, use your package manager to try to locate them, as described for KDM in the previous section. The main GDM configuration file is called gdm.conf, and the section that's most relevant to XDMCP server operation is called [xdmcp]. To enable remote logins, be sure that this section includes the following lines:

Enable=true Port=177

If you want to accept remote XDMCP logins without starting X locally, locate the [servers] section of gdm.conf. This section normally contains a line such as the following:

0=Standard vt7

Comment out this line by adding a hash mark (#) to the start of the line and GDM won't start X on the local system when it's restarted. (You may need to switch to runlevel 3 and then back to runlevel 5 to restart GDM without X.)

Instead of editing the configuration file in a text editor, you can use a GUI tool. Type gdmsetup in an xterm window or select the option for the GDM configuration tool, often called Login Screen, GDM Configurator, or something similar, from a desktop environment menu. The result is the GDM Setup window, as shown in Figure 26.2. The XDMCP tab includes the XDMCP options, the most important of which is the Enable XDMCP check box. Be sure the program is set to listen on UDP port 177, as well.

Figure 26.2: GDM provides a GUI configuration tool in which you can activate XDMCP options.

If you want to make additional login environments available to GDM users, you can add scripts to the /etc/X11/gdm/Sessions directory. Once you add a script, it becomes available as an option on the Session menu in the login dialog. If a user selects that option, the script you created runs as the user's login script. The default scripts usually call /etc/X11/xdm/Xsession with the name of the environment that's to be run.

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