Comment 6 for bug 1581853

From my reading of the above, it seems that this bug should be fixed in Yakkety, and probably also in up-to-date installations of Xenial.

I believe this is the bug I'm currently seeing (prefs.sh not sourced as privileged user) in both Yakkety and Xenial (lightdm versions 1.19.5-0ubuntu1 and 1.18.3-0ubuntu1 respectively). Should I open a new bug report tagged regression-update as mentioned above, or have I misunderstood in thinking it should be fixed in these versions?

The symptom I'm seeing is that if I put commands into /etc/guest-session/prefs.sh requiring execution by a privileged user, the guest login loops back around to the login screen without any messages. Behaviour is the same in both Yakkety and Xenial with all packages up-to-date.