I want to copy some data from another machine to a local computer on a regular basis. At the moment I'm researching different solutions and try to find the one which fits best.

Basically I want to open a network connection (or use an existing one), make a VPN connection and start a rsync process. This should be done on every logout of my desktop session or on shutdown.

One possible solution might be to somehow intercept the Unity shutdown and execute a script. So is there a possibility to execute a script on GNOME/Unity shutdown? I'm aware that you can do it on system shutdown. How can I do this?