lightdm-gtk-greeter uses 100% CPU and shows gray screen

[Reed O'Brien]

DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=15.04
DISTRIB_CODENAME=vivid
DISTRIB_DESCRIPTION="Ubuntu 15.04"

Package: lightdm-gtk-greeter 2.0.0-0ubuntu1

ubuntu-bug output is attached with deatiled system info.

After upgrading Xubuntu from 14.10 to 15.04 the log in screen remains gray and the lightdm-gtk-greeter process consumes 100% CPU on one core.

I expected a login screen. When stopping/starting the service with
systemctl [re]start|stop lightdm.service

I recieved "Error: No space left on device." as an error. This was misleading as I don't have a space issue.

I added "allow-debugging=true" to "/etc/lightdm/lightdm-gtk-greeter.conf" then I restarted lightdm.

In the log I could then see that the greeter was switching between active monitors endlessly.

...
DEBUG-Message: [Background] Active monitor changed to: HDMI1 #1
DEBUG-Message: Read 8 bytes from daemon
DEBUG-Message: Read 37 bytes from daemon
DEBUG-Message: Prompt user with 1 message(s)
DEBUG-Message: [Background] Active monitor changed to: DP1 #0
DEBUG-Message: [Background] Active monitor changed to: HDMI1 #1
DEBUG-Message: [Background] Active monitor changed to: DP1 #0
DEBUG-Message: [Background] Active monitor changed to: HDMI1 #1
DEBUG-Message: [Background] Active monitor changed to: DP1 #0
DEBUG-Message: [Background] Active monitor changed to: HDMI1 #1
DEBUG-Message: [Background] Active monitor changed to: DP1 #0
DEBUG-Message: [Background] Active monitor changed to: HDMI1 #1
DEBUG-Message: [Background] Active monitor changed to: DP1 #0
DEBUG-Message: [Background] Active monitor changed to: HDMI1 #1
DEBUG-Message: [Background] Active monitor changed to: DP1 #0
DEBUG-Message: [Background] Active monitor changed to: HDMI1 #1
DEBUG-Message: [Background] Active monitor changed to: DP1 #0
DEBUG-Message: [Background] Active monitor changed to: HDMI1 #1
DEBUG-Message: [Background] Active monitor changed to: DP1 #0
DEBUG-Message: [Background] Active monitor changed to: HDMI1 #1
DEBUG-Message: [Background] Active monitor changed to: DP1 #0
DEBUG-Message: [Background] Active monitor changed to: HDMI1 #1
DEBUG-Message: [Background] Active monitor changed to: DP1 #0
DEBUG-Message: [Background] Active monitor changed to: HDMI1 #1
...

So I set
"active-monitor=0" and restarted lightdm. This solved the issue.

I suspect this may only happen with multi monitor setups and on mirrors displays that have a cursor on both. This is unclear to me though.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: lightdm-gtk-greeter 2.0.0-0ubuntu1
ProcVersionSignature: Ubuntu 3.19.0-15.15-generic 3.19.3
Uname: Linux 3.19.0-15-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.17.2-0ubuntu1
Architecture: amd64
CurrentDesktop: XFCE
Date: Fri Apr 24 12:09:07 2015
InstallationDate: Installed on 2014-08-06 (261 days ago)
InstallationMedia: Xubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140416.2)
SourcePackage: lightdm-gtk-greeter
UpgradeStatus: Upgraded to vivid on 2015-04-24 (0 days ago)

[Reed O'Brien (reedobrien)]

Looks like a dupe of bug #1410406

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Robert Stiffler (rstiffler92)]

I have a multiple monitor setup also. Adding "active-monitor=0" to /etc/lightdm/lightdm-gtk-greeter.conf fixed the issue.