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

[Adam Nielsen]

> I am seeing lightdm run fine for a couple days, then while there is
> still an active user session on seat-1, it decides it needs to create
> a greeter session on seat-1.  That fails repeatedly, with it
> attempting to create the greeter session 30-50 times per second.  This
> quickly fills up the log file to many Gb, and uses significant CPU.

This isn't a LightDM problem.  What is happening is that your machine
is configured to start a second seat (seat-1), which causes LightDM to
load as the login handler for that seat.  In order to provide this it
launches another X instance, which then complaints that it hasn't been
set up with a display device - perhaps you only have one and it's in
use by the existing seat.

To fix the problem, either configure your system to only have one seat,
or configure X11 with appropriate devices so that it can bring up the
second seat without error.

Cheers,
Adam.