- On start up reads its configuration from the folder $KDEDIR/share/config/kdm/ (or /etc/kde4/kdm/ - could vary).
- The main configuration file is $KDEDIR/kdmrc. All other files are referenced from this file and therefore could be stored under any name anywhere on the system.
'kdm' is usually added to /etc/inittab.
kdm inittab entry
or if no inittab (as in ubuntu and ubuntu based distros) ..
Set as default display manager - /etc/X11/default-display-manager
Find the line like /etc/ttys in /etc/inittab
ttyv8 "/usr/X11R6/bin/xdm -nodaemon" xterm off secure
and change to something like
ttyv8 "/opt/kde/bin/kdm" xterm on secure
Most other distributions will be a variation of one of these. The runlevel for X varies on distributions e.g. Ubuntu is 2.
Basically, the X server starts, then it looks to see which display manager it should run.
Test it - /sbin/init
# /sbin/init 5
On ubuntu use 2 instead of 5.
Boot to multi-user X window envirmonment - /etc/inittab
On ubuntu use 2 instead of 5. On reboot should end up with the graphical kdm login dialog.