[root@couch gdm-2.4.0.7]# rpm -q gdm
gdm-2.4.0.7-13

-----------------------------------
post null testing ...

I may have this set entirely wrong, but see:

http://www.owlriver.com/tips/gdm-setup/

which is a response to getting GDM compiling local XDMCP traffic and offered
Server hosts.

The two paths to authentication are gdmgreeter (for local host connections), and
gdmlogin (for remote ones).  gdm itself can manage shutdown as well ...

Problem:  There is no filesystem safe way for gdmgreeter to halt (shutdown) the
server host.  The end user has to log in, and sudo or su to root, and execute a
halt. -- not something most admins want to allow an unrestricted right to end
users to do.

It seems that /etc/X11/gdm/gdm.conf needs an option stanza for the gdm daemon
host selection panel to offer a Shutdown (possibly only for authorized users),
or for gdmgreeter to add a shutdown option -- here, permitting authentication
against the PAM handled passwd/shadow file, and being a better way to handle the
matter.

For some reason (probably simply historical), it is present with gdmlogin
already ...