lightdm only shows black screen with cursor on 17.10

[Achim Behrens]

after recent updates on 17.10 (development) lightdm fails. It only shows a black screen and the cursor. Cant change to tty1 with ctrl+alt+f1.

started from grub with systemd.unit=multi-user.target into tty1 and started gdm from there, so i could log on to unity (with broken gtk).

nothing obvious for me in the log files from syslog or lightdm.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: lightdm 1.24.0-0ubuntu1
ProcVersionSignature: Ubuntu 4.13.0-15.16-generic 4.13.4
Uname: Linux 4.13.0-15-generic x86_64
ApportVersion: 2.20.7-0ubuntu3
Architecture: amd64
CurrentDesktop: Unity:Unity7:ubuntu
Date: Thu Oct 12 17:15:29 2017
InstallationDate: Installed on 2013-09-28 (1475 days ago)
InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Beta amd64 (20130925.1)
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: lightdm
UpgradeStatus: Upgraded to artful on 2017-06-30 (104 days ago)