session-manager fails to recognize inhibitor

[Jan Niggemann <jn hz6 de>]

Hi list,

when GNOME applications have unsaved data and the user wants to 
shutdown, the session manager (?) informs the user about this on the 
lightbox-popup with the choices "cancel, restart, shutdown". I believe 
that this is done via dbus 
(http://www.lucidelectricdreams.com/2011/06/disabling-screensaverlock-screen-on.html) 
and I can successfully register an inhibitor using the python example 
given there. I'd like to use this mechanism for my console backup 
application, so I don't shut down my laptop when a backup is running.

My problem is that the inhibition and the "reason" are not shown during 
log out on GNOME 3.4 (Debian stable 32bit). Why is that?

I downloaded the gedit source to check how gedit handles this, but it 
uses a GTK+ call:
https://developer.gnome.org/gtk3/stable/GtkApplication.html#gtk-application-inhibit

Can anyone give me an idea how I can inhibit shutdown using dbus (I 
know that this isn't 100% sure as users could override it)?

Regards
jan