lightdm-gtk-greeter hangs, leaving session locked with gray screen

[Lars W]

On a fresh Xubuntu 15.04 install, I created a new user. When I lock the session (or resume from standby, which also locks the session), I see nothing but a screen in light gray. After about a minnute, the screen goes black (power safe), pressing any key brings back the gray screen. There is no possibility to unlock the session. Ctrl+Alt+F1 brings me to terminal, where I can see with `top` that "lightdm-gtk-greeter" takes 100% CPU.

The log contains warnings about background images that can not be read. I believe those are warnings only and not fatal errors.

Version of lightdm-gtk-greeter: 2.0.0-0ubuntu1.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: lightdm 1.14.2-0ubuntu1
ProcVersionSignature: Ubuntu 3.19.0-28.30-generic 3.19.8-ckt5
Uname: Linux 3.19.0-28-generic x86_64
ApportVersion: 2.17.2-0ubuntu1.4
Architecture: amd64
CurrentDesktop: XFCE
Date: Sat Sep 12 10:02:29 2015
InstallationDate: Installed on 2015-09-03 (8 days ago)
InstallationMedia: Xubuntu 15.04 "Vivid Vervet" - Release amd64 (20150422.1)
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)

[Lars W (lavs)]

I disabled all crypto partition and the problem persists. (I previously had an encrypted home partition, unlocked with libpam-mount. Now, I used a new user with no crypto at all.) I also started lightdm-gtk-greeter-settings to disable the background image and user image, to make the warnings go away. But the problem still persist. The log still contains nothing that looks suspicious to me (expect maybe "DEBUG: Got 1 message(s) from PAM" doesn't say which one).

After about 30min of gray screen, I went to terminal and started gdb -p $pid, where $pid is the process id of the 100% CPU process lightdm-gtk-greeter, to attach a debugging session and see where the process hangs. Interestingly, after ~20 debug steps, it runs again and waits for user input. I go back to Ctrl+Alt+F8, and can log in again! (what the...?)

After login, I see a prompt for authentification with org.freedesktop.accounts.change-own-user-data . Maybe it is related to that?

[Thomas Uhl (t-uhl)]

Nearly the same here:
ubuntu-studio-15.04 amd64
After fresh install on partition /dev/sda7 (have multiple other ubuntu derivates on sdaX)
and the first boot, the screen hangs in grey as described before for minutes until I gave up. CPU consumption varies, but always more than 90%. service lightdm restart with no success.
Other boot options from boot-menu (extended, recovery, non-lowlatency) makes no difference.
Same with an preinstalled standard ubuntu 15.04 and later installed ubuntu-studio packages.
Installation Date: 20.Sept.2015 all updates installed so far.

Hardware: HP ProBook 450 G1. 2 Displays (second via HDMI 1920x1080), cordless keyboard and USB2.0 mouse.

[Andrew P. (kalgasnik)]

15.04 have 2.0.0 version, use stable PPA to check 2.0.1:
https://launchpad.net/~lightdm-gtk-greeter-team/+archive/ubuntu/stable

[Lars W (lavs)]

YES! This update and deleting my .config (`my ~/.config ~/.config.bak`) fixed it for me.

I can lock the session and log back in again, resume also works. :-)