LightDM fails to switch to greeter on logout if allow-user-switching=false

[Laércio de Sousa]

In my multiseat system, if I logout on a non-seat0 seat (which has allow-user-switching=false by default), lightdm fails to start a greeter on that seat:

DEBUG: Seat: Display server stopped
DEBUG: Seat: Active display server stopped, starting greeter
DEBUG: Seat: Stopping; failed to start a greeter
DEBUG: Seat: Stopping
DEBUG: Seat: Stopped

I guess the problem is related to seat_switch_to_greeter() calls in session_stopped or display_server_stopped callbacks in seat.c. Switch to greeter should be always allowed on logout.

NOTE: This was observed in LightDM 1.10.2 on Ubuntu 14.04, but I guess it also happens on trunk series.

[Laércio de Sousa (lbssousa)]

Until this bug can be fixed, LightDM should ship a default configuration in /usr/share/lightdm/lightdm.conf.d enabling "allow-user-switching" explicitly, or comment out this code piece at line 980 of file lightdm.c:

        if (!login1_seat_get_can_multi_session (login1_seat))
        {
            g_debug ("Seat %s has property CanMultiSession=no", seat_name);
            seat_set_property (seat, "allow-user-switching", "false");
        }

[Robert Ancell (robert-ancell)]

We're currently working around this issue with the merges done by Laércio. So now we need to disallow user switching but still be able to return to a greeter on logout.

[Laércio de Sousa (lbssousa)]

Should we adopt the following solution for this bug?

If allow-user-switching=false for a given seat, a seat_switch_to_greeter() call on that seat implies logout for current user.

[Charles Wright (wrighrc)]

Hello,

I'm using multiseat under ubuntu lts 16.04

I found a description of what is happening here:
https://lists.launchpad.net/ubuntu-multiseat/msg00505.html

In short, seat-1 lock/switch user doesn't work and generates tons of error logs

[+763003.64s] DEBUG: Launching process 27821: /usr/bin/X :1 -s seat-1 :2 -config /etc/X11/xorg.conf.nvidia -seat seat-1 -auth /var/run/lightdm/root/:2 -nolisten tcp
[+763003.69s] DEBUG: Launching process 27822: /usr/bin/X :1 -s seat-1 :2 -config /etc/X11/xorg.conf.nvidia -seat seat-1 -auth /var/run/lightdm/root/:2 -nolisten tcp
[+763003.74s] DEBUG: Launching process 27823: /usr/bin/X :1 -s seat-1 :2 -config /etc/X11/xorg.conf.nvidia -seat seat-1 -auth /var/run/lightdm/root/:2 -nolisten tcp
[+763003.79s] DEBUG: Launching process 27824: /usr/bin/X :1 -s seat-1 :2 -config /etc/X11/xorg.conf.nvidia -seat seat-1 -auth /var/run/lightdm/root/:2 -nolisten tcp
[+763003.84s] DEBUG: Launching process 27825: /usr/bin/X :1 -s seat-1 :2 -config /etc/X11/xorg.conf.nvidia -seat seat-1 -auth /var/run/lightdm/root/:2 -nolisten tcp

I configured allow-user-switching=false so that my logs won't fill up.

[Seat:seat-1]
xserver-command=/usr/bin/X :1 -s seat-1
xserver-config=/etc/X11/xorg.conf.nvidia
# This kept constant respawn of X from filling up logs, but only allows one login - greeter fails to start
allow-user-switching=false

Now what happens, just as reported in this bug is that I can start lightdm, and someone can login once to seat-1, but once they log out there is no greeter respawned.

I think this bug should be updated to include Xenial as well.

Anyways I'm sure multiseat is a rare thing but I wanted someone to know it matters to me.

I'm so close to having it work!

Is there anything else I can try to work around?

I see the question above:

"Should we adopt the following solution for this bug?"

I vote yes to that.

Thanks.