don't allow shut down if there are other user with opened sessions

Binary package hint: gnome-session

I tried to find a answer for this problem, but I could only find a way to completly disable shutdown and suspend.

I have one administrator account that I'm using and other simple user account for my friends.

When my friends come and visit me, they want to use my computer just for a short time and then log off.
To do this I'm using the switch user feature.

When they are done, they should just "Log off" , but some of them, instead of log off, they push the shut down button. Durring all this time my main gnome session is running and at the shutdown I loose all my work.

I would like GNOME to warn me about the existence of other running gnome-sessions.

If I'm not an administrator and there are other running session I should be allow only to log off.

If I'm an administrator I should be warned, but have an option to force shutdown.

Hibernate and suspend should be allowed as the session can be recoverd.

I'm sorry if this is a duplicate, but I did not know how to search this problem.

Many thanks!