[Timed] Autologin fails if user is selected in user list

[Laércio de Sousa]

I work with a computer lab consisting of 9 CPUs with 2 seats each one. I have used Ubuntu 14.04 LTS on them and now I'm trying Ubuntu 15.04. In both cases, I set autologin as guest in all seats with a timeout of 60 seconds.

After some reboots, I've noticed that one of the seats stops performing autologin after the timeout. However, if I set autologin timeout to 0 on that seats, they perform autologin as expected.

Once timed autologin starts to fail on some seats, it won't go back to normal, even if I reboot or power off the computer. It only goes back to normal if I reinstall lightdm.

[UPDATE] I realised that timed autologin actually fails if user in question (also applies for guest) is selected in user list when timeout reaches 0. However, if I select another user before timeout reaches 0, autologin for configured user works as expected. Got hint from https://bugs.launchpad.net/lightdm/+bug/854261/comments/5

Verified with lightdm-gtk-greeter. Not sure if it also happens with other greeters.

[Hb (hbb)]

Is this bug somehow related to Bug 854261 ?

[Laércio de Sousa (lbssousa)]

I can confirm this with lightdm-gtk-greeter at Xubuntu 15.04.

I have lightdm configured to autologin as a given user (also applies for guest) on both seats. If the user configured for autologin on a given seat is selected in user list when timeout reaches 0, it won't autologin. However, if I change the user selected before timeout reaches 0, autologin works as expected.

Not sure if it also happens for unity-greeter.

[Laércio de Sousa (lbssousa)]

I guess I may have found a better explanation about this bug.

Whenever a user is switched in greeter, i.e. a new user selection is made in greeter's user list, LightDM immediately sets its PAM authentication service to either "manual" (set by option [Seat*]/pam-service) or "autologin" (set by option [Seat*]/pam-autologin-service).

When autologin timeout expires, user currently selected in greeter's user list is switched to that one set in [Seat*]/autologin-user option, which in turn sets its PAM authentication service to "autologin", and then performs the login.

However, if the user selected in greeter's user list matches that one set in [Seat*]/autologin-user in the moment autologin timeout expires, then no user switching is performed, and no autologin is triggered.

If my assumption is right, maybe we can fix the bug by forcing lightdm to "switch user to itself" when autologin timeout expires.

Robert, what do you think about it?