2. Introduction

This info is based on my RedHat 6.1 default KDE Workstation installation. If you are using another distribution, or even another version of RedHat, or a different Workstation install, then you may have to do some detective work. Hopefully, this info will give you what you need to start detecting! This HOWTO began as the result of wondering how to add another window manager or desktop environment to the drop-down list on the GUI login screen; further investigation revealed other configuration options.

I began my own "detective work" when I found a reference on a RedHat List which mentioned /etc/inittab, and its role in system startup. In /etc/inittab I found the following entries, which define how the X Window System is started in my distribution and version:

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# Run xdm in runlevel 5
# xdm is now a separate service
x:5:respawn:/etc/X11/prefdm -nodaemon

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Here is what prefdm looks like:

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#!/bin/sh

PATH=/sbin:/usr/sbin:/bin:/usr/bin:/usr/X11R6/bin

# Run preferred X display manager
preferred=
if [ -f /etc/sysconfig/desktop ]; then
        if grep -q GNOME /etc/sysconfig/desktop 2>/dev/null; then
                preferred=gdm
        elif grep -q KDE /etc/sysconfig/desktop 2> /dev/null; then
                preferred=kdm
        elif grep -q AnotherLevel /etc/sysconfig/desktop 2> /dev/null; then
                preferred=xdm
        fi
fi
if [ -z ":$preferred" ]; then
        if which gdm >/dev/null 2>&1; then
                preferred=gdm
        elif which kdm >/dev/null 2>&1; then
                preferred=kdm
        elif which xdm >/dev/null 2>&1; then
                preferred=xdm
        fi
fi
if [ -n "$preferred" ] && which $preferred >/dev/null 2>&1; then
        exec `which $preferred` $*
fi
exit 1  

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No changes to prefdm are necessary; it determines which display manager is the system default, and which runs the GUI login. During boot-up, prefdm parses /etc/sysconfig/desktop and selects the display manager listed there; in the case of my KDE Workstation install, this is kdm (KDE Display Manager). Note that gdm (Gnome Display Manager) is not installed on my system; xdm (X Display Manager) is installed by default as part of the X Window System, and was apparently used by older versions of Red Hat.