I have some kiosk PCs that pretty much work like the Ubuntu guest session. The kiosk users home has a union filesystem mounted on top of it so the can't change anything but can still save files while working at the machine (and take them with them using a USB key).
Users sometimes leave the stations with private stuff still on the desktop. Because of that I want them logged out after - say - 10 minutes of inactivity (the union file system will be emptied on logout).
Any ideas if there is an existing solution (autolog only logs the user out of active terminal sessions).