On Tue 07 Jun 2011 at 19:57:57 +0100, Brian wrote: > So it's mystifying! All users get to shutdown the machine if sudo is on > the it. Mystery cleared up. I could have been more thorough in what I did and checked everything. Installing sudo ungreys the buttons in the session closing dialogue and rebooting or shutting down is permissable for users in the sudo group or if /etc/sudoers allows it. Otherwise permission is denied.