This seems to be caused by the following change in lightdm upstart configuration (introduced in 1.2.3-0ubuntu2.1):
$ diff init.working/lightdm.conf init.broken/lightdm.conf 14,15c14 < and (drm-device-added card0 PRIMARY_DEVICE_FOR_DISPLAY=1 < or stopped udev-fallback-graphics)) --- > and plymouth-ready)
This seems to be caused by the following change in lightdm upstart configuration (introduced in 1.2.3-0ubuntu2.1):
$ diff init.working/ lightdm. conf init.broken/ lightdm. conf DEVICE_ FOR_DISPLAY= 1 graphics) )
14,15c14
< and (drm-device-added card0 PRIMARY_
< or stopped udev-fallback-
---
> and plymouth-ready)