GNOME Bugzilla – Bug 794167
gdm 3.27 shows blank login screen on primary monitor when two monitors are connected
Last modified: 2018-03-23 04:02:21 UTC
With an external monitor plugged into my laptop, when I boot gdm 3.27 I get presented with a blank (totally black) login screen on the (4k) login screen. I can see (and move) the mouse cursor, so the monitor is turned on. The external monitor shows a background screen. At this point I can hit the enter key and a password and provided I have guessed at the correct password for whichever user is selected by default I get logged in. Otherwise, if I unplug the external monitor, gdm redraws the login window properly so I can see my users. I originally reported this at https://bugs.launchpad.net/ubuntu/+source/gdm3/+bug/1754218 so there's more version info there. Ubuntu released version 3.27 quite recently (http://changelogs.ubuntu.com/changelogs/pool/main/g/gdm3/gdm3_3.27.90-0ubuntu1/changelog), and I have only noticed this bug very recently, so it looks like a regression since version 3.26.
FWIW, this could be related to either intel graphics or intel/nvidia hybrid graphics (I tried the latest Ubuntu 18.04 in a VirtualBox machine with two displays enabled and didn't run into the problem). On the hybrid graphics laptop where I see this issue, I have prime-select installed with the intel profile selected, and I'm using the nvidia-390 module together with bbswitch and bumblebeed to turn off the nvidia card.
Using two monitors (one Intel GPU) with gdm3 3.27.90-0ubuntu1, I cannot reproduce this problem. Sounds like it is more related to nvidia than the multi-monitor.
Sounds like maybe we should be looking to mutter instead, if not the nvidia driver... https://gitlab.gnome.org/GNOME/mutter/issues
Re mutter, that could make sense - apparently the latest mutter was released just a few days ago according to https://launchpad.net/ubuntu/+source/mutter/3.27.92-1. A couple of observations: 1. If I switch to, say, tt3 and then back to tty1 (where gdm is supposed to show the login screen), gdm switches the external monitor back to showing an Ubuntu login screen background, but the primary monitor keeps showing the tty3 screen (along with a mouse cursor). 2. If I log off so that it goes back to gdm's login screen, I get the same issue (ie it's not just on boot). Could it be related to libglvnd0? This has recently been added to Ubuntu, and in the past it made mutter and gnome-shell default to llvmpipe instead of the Intel driver (gnome-shell now runs OK using the Intel driver, though). I am curious though as to why gdm/mutter would work on one monitor but not the primary monitor just because there are (disabled) nvidia drivers installed?
I've also got a debug log from mutter but bugzilla is giving me an error 500 when I try to post it.
Removing the nvidia-390 package (and having no nvidia drivers installed) makes no difference.
Created attachment 369559 [details] mutter gdm log
light-dm works fine, it's just gdm3 that has this issue.
FWIW, the problem persists using mutter 3.28.0-1 and nvidia 387.
I think it's fixed now so I'll try and mark it resolved. FWIW I have now got gdm 3.27.92-0ubuntu1, mutter 3.28.0-1, and mesa 18.0.0-rc5 drivers installed.