This tool is used to send messages between the system and users' accounts. For each X11 session a small program called s2u is launched under an X11 dbus session (using existing one if possible). The s2u program waits then for dbus messages to take the appropriate actions. The implemented actions are: o react to hostname changes to continue to have a working X11 session. o run update-menus if requested by the system o display msec notifications o display custom notifications (netprofile, ...)