To stop GDM, you can either send the TERM signal to the main daemon or
run the gdm-stop command which is in the
<sbin>/ directory.  To restart GDM, you can
either send the HUP signal to the main daemon or run the
gdm-restart command which is also in the
<sbin>/ directory.  To restart GDM but only
after all the users have logged out, you can either send the USR1
signal to the main daemon or run the
gdm-safe-restart command which is in the
<sbin>/ directory as well.
The gdmflexiserver command can be used to start
new flexible (on demand) servers.  Run
gdmflexiserver --help to get a listing of possible
options.  This command will also lock the current screen with
gnome-screensaver so that the user can safely walk away from the computer and
let someone else log in.  XFree86 will automatically switch back to the
same virtual terminal (if your operating system supports it), after the
new session has ended, so this should work quite transparently to the
users.
