Shutdown or Reboot

[Christoph Pleger <Christoph Pleger cs tu-dortmund de>]

Hello,

which action is performed when someone clicks on the menu item "System ->
Shut Down -> Shut Down" or "System -> Shut Down -> Restart" and where is
that action defined?

So far, I found out that somehow /sbin/shutdown is called, but I do not
know why it is executed with root privileges.

Regards
  Christoph