Comment 5 for bug 1318679

The expectation here, is that root user is able to control any user-sessions of any user, by setting appropriate UPSTART_SESSION variable.

If you wish to control system init, please either:
1) pass --system argument
2) unset, or set to empty UPSTART_SESSION

Alternatively we can fix this by:
1) if root, use system init irrespective of UPSTART_SESSION environment variable
2) if root, and "--session" argument is passed, operate against UPSTART_SESSION or bail out if one was not specified / does not exist.