I now installed only ubuntu-gnome-default-settings on a second PC with the same problem and changed back to gdm. It worked there as well. So a fix for this problem seems to be contained in this packet.
-- You received this bug notification because you are a member of Desktop Packages, which is subscribed to gdm in Ubuntu. https://bugs.launchpad.net/bugs/1500673 Title: gdm unusable after upgrading to 15.10 Status in gdm package in Ubuntu: Confirmed Bug description: Hi there -- I figured I'd try 15.10 a few days before release, and when gdm is the default greeter, I see no login prompt and I have to CTRL-ALT-F1 to get to a terminal. As far as I can tell, there's nothing interesting in the logs in /var/log or /var/log/gdm. I just get a blank, black screen. As a side note, I'm seeing the error messages described in https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1492764, but I don't think they are the root cause for a missing X-server (AFAICT, there's no X server starting). Please advice on how I can troubleshoot further. `dkg-reconfigure gdm` and choosing lightdm yields a GUI login prompt in lightdm. ProblemType: Bug DistroRelease: Ubuntu 15.10 Package: gdm 3.16.2-0ubuntu2 ProcVersionSignature: Ubuntu 4.2.0-11.13-generic 4.2.1 Uname: Linux 4.2.0-11-generic x86_64 ApportVersion: 2.19-0ubuntu1 Architecture: amd64 Date: Mon Sep 28 20:15:50 2015 InstallationDate: Installed on 2014-07-02 (453 days ago) InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417) SourcePackage: gdm UpgradeStatus: Upgraded to wily on 2015-09-29 (0 days ago) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gdm/+bug/1500673/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp