HWE 16.04.2: Login Screen goes partially black after upgrade (Dual Screen)

[Thomas Mayer]

I'm using ubuntu 16.04, up-to-date, HWE kernel 4.8.0-36-generic.

On dual screen setup, during system login, the first screen stretches over a part of the second screen (about 25% of it), whereas the rest of the second screen is black. Like this:

############ ############
# # #<<|.......#
# Login # #<<|.Black.#
# # #<<|.......#
############ ############

The part marked with "<<" is the rightest part of the background image of the first screen. I've seen this after updating to xorg/xserver-hwe-16.04, whereas installing the hwe kernel alone did not make this happen.

Nevertheless, I can login and everything is fine again. Both screens look as they should. (I had to reconfigure monitors once after updating to xorg/xserver-hwe-16.04).

sylog shows:

Feb 18 06:27:03 lat61 gnome-session[3242]: ** (gnome-flashback:3340): WARNING **: Could not assign CRTC to outputs, ignoring configuration
Feb 18 06:27:03 lat61 gnome-session[3242]: ** (gnome-flashback:3340): WARNING **: Could not make default configuration for current output layout, leaving unconfigured

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: gnome-flashback 3.18.2-1ubuntu1
ProcVersionSignature: Ubuntu 4.8.0-36.36~16.04.1-generic 4.8.11
Uname: Linux 4.8.0-36-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.5
Architecture: amd64
CurrentDesktop: GNOME-Flashback:Unity
Date: Sat Feb 18 07:46:46 2017
InstallationDate: Installed on 2014-11-29 (812 days ago)
InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
SourcePackage: gnome-flashback
UpgradeStatus: Upgraded to xenial on 2016-06-15 (247 days ago)

[Thomas Mayer (thomas303)]

That got scrambled. Should be:

############_############
#----------#_#<<|.......#
#-Login----#_#<<|.Black.#
#----------#_#<<|.......#
############_############

Again, The part marked with "<<" is the rightest part of the background image of the first screen.

[Thomas Mayer (thomas303)]

As it turned out, the leftern part of the right screen is already part of the right screen (not a overstretched part of the left screen.

To illustrate it, I marked it red on a photo (attached).

Still: 80% of the second screen remain black, as long as the login process is not finished.

[Dmitry Shachnev (mitya57)]

Your photo shows the lightdm login screen, and you tell that after login everything is fine. Maybe reassign this to lightdm?

[Alberts Muktupāvels (muktupavels)]

This definitely is not problem with gnome-flashback, at login screen gnome-flashback is not started.

Don't know if that will work for you, but once it worked for me. You could try to copy your working /home/{your-user}/.config/monitors.xml file to /var/lib/lightdm/.config/monitors.xml. If that does not help remember to delete it from /var/lib/lightdm/.config

Other option might be to create /etc/X11/xorg.conf with correct configuration. Or if you already have one then maybe try to temporarily remove it.

Since you say that happens after updating to xorg/xserver-hwe-16.04 that could indicate that this is bug/regression in xorg.

[Thomas Mayer (thomas303)]

@mitya57 @muktupavels thanks for reporting back.

Directory /var/lib/lightdm was empty in my case:

/var/lib/lightdm# ls -lh #as root user
insgesamt 0

Copying

/home/<user>/.config/monitors.xml

to

/var/lib/lightdm/monitors.xml

does not fix this issue.

[Thomas Mayer (thomas303)]

The path was wrong in #6 (I forgot the /.config/

Copying

/home/<user>/.config/monitors.xml

to

/var/lib/lightdm/.config/monitors.xml

fixes this issue for me (see image attached).

Btw.: After upgrade to new HWE/Xorg I had to resize my monitors to get rid of similar situations for the gnome session itself. That could be done by reajusting resolution two times (go for wrong resolution and back to right resolution). But that could be done via GUI (system settings/displax devices). Be that a bug in itself or not, I think it is not convenient, at least.

However, the GUI setting did not affect lightdm monitor settings. Only copying monitors.xml to /var/lib/lightdm/.config/ did.

For lightdm, I think this is a bug, just because it requires non-GUI user interaction. Average users should not be tricked into such situations.

[Thomas Mayer (thomas303)]

I still get syslog entries

Feb 18 20:16:52 lat61 gnome-session[3090]: ** (gnome-flashback:3185): WARNING **: Could not assign CRTC to outputs, ignoring configuration
Feb 18 20:16:52 lat61 gnome-session[3090]: ** (gnome-flashback:3185): WARNING **: Could not make default configuration for current output layout, leaving unconfigured

Now that the login screen works correctly (after manual intervention), I think this is a separate issue, which should be handled with a separate bug #1665922

[Paul White (paulw2u)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. We are sorry that we do not always have the capacity to review all reported bugs in a timely manner.

Ubuntu 16.04 (xenial) reached end-of-standard-support on April 29, 2021.

I'm setting the status of this bug to 'Incomplete' as it's not seen any activity for some time. If this is still an issue when using a currently maintained release of Ubuntu then please let us know which one(s) otherwise this bug report can be left to expire in approximately 60 days time.

[Launchpad Janitor (janitor)]

[Expired for lightdm (Ubuntu) because there has been no activity for 60 days.]

[Launchpad Janitor (janitor)]

[Expired for xorg (Ubuntu) because there has been no activity for 60 days.]