[LightDM] lightdm goes into tight loop trying to create greeter sessions and fills up logs

[Adam Nielsen]

> Did you look at the logs I posted on
> the debian bug report?  After being started, lightdm runs fine on both
> seat0 (VT7) and seat-1.

I can't see any X logs for the successful sessions, only one X log
where it complains that there's no display device and terminates, which
causes LightDM to try to restart X, which leads to the loop you
mentioned.

> The greeter remains running on seat0 (I am
> logged in directly from the VT1 console terminal, where I started X
> the old fashioned way) and my son has an active session on seat-1
> where he logged in via lightdm/greeter.

I think I can see this in the logs, and it looks like seat-1 logs out
and back in once, successfully.

> About 2-3 *days* later, it
> decided that it needed to start a greeter on seat-1, and went into a
> tight loop failing repeatedly.  I included the complete lightdm log up
> until it starts looping.  Have been through several cycles of this,
> and it seems to reliably happen a few days after restarting lightdm.

It looks like something is triggering LightDM to run again on seat-1.
This itself isn't a problem, as you can run `dm-tool switch-to-greeter`
to start multiple sessions on the same seat (they each start on a
different VT and you can switch between them like any other VTs).

I am wondering whether something is causing this to happen in your
case?  What happens if you use dmtool like this to start another
session, do you get another one running on that seat, or does it
trigger a similar loop?

I presume you have configured the seats manually in the X config files.
I am wondering why it is trying a whole bunch of display drivers (ati,
amdgpu, modesetting, vesa, etc, etc.) before complaining that it can't
find a valid display.  This normally only happens if you haven't
specified a device in xorg.conf.  It's telling you to specify the BusID
in xorg.conf but if you've manually configured the seats I would've
expected you to already have done this.

Cheers,
Adam.