gnome-session: how to shutdown gnome-session from root?

[Stefano Sabatini <stefano sabatini-lala poste it>]

Hi all, 

I would like like to setup acpid to automatically launch the
gnome-session-save program when the power button is pressed (and gnome
is running).

The problem is that when I run from the power-button associated script
the command:

sudo gnome-session-save --gui --kill

I get this message in a GTK error window dialog:

"Could not connect to the session manager"

I've tried this either running sudo with the identity of the owner of
the gnome-session user with:

sudo -u <gnome username> gnome-session-save --gui --kill

getting the same result.
I'm using gnome-session 2.14.3 (Debian unstable).	

How can I convince gnome-session-save to execute the command launched
by root?  
Is there another system to shutdown automatically and gently gnome
(maybe sending some signal to the gnome-session process)?

Thanks in advance for any help.

Cheers

-- 
Stefano Sabatini
Linux user number 337176 (see http://li.count.org)