Lxdm black screen after Ubuntu 21.04 upgrade

[Boris Gjenero]

In the past I used lxdm on my Dell Inspiron 6400 laptop without problems. After upgrading from Ubuntu 20.10 to 21.04, lxdm shows a fully black screen, without even a mouse cursor. Attempts to interact with it blindly don't work, which suggests it's somehow hanging, and not simply failing to display.

Installing lxdm_0.5.3-2.1_amd64.deb from Ubuntu 20.10 does not fix the problem. So maybe something else is at fault, because that lxdm worked in Ubuntu 20.04.

The laptop has Mobility Radeon x1400 with the radeon driver. Though using the fbdev driver instead doesn't change this bug.

I don't use LXDE and don't have it installed. I'm only using lxdm because it is lightweight and fast, and I prefer other desktop environments. This has never been a problem in the past.

ProblemType: Bug
DistroRelease: Ubuntu 21.04
Package: lxdm 0.5.3-4
Uname: Linux 5.12.0-051200rc5-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.11-0ubuntu61
Architecture: amd64
CasperMD5CheckResult: unknown
CurrentDesktop: XFCE
Date: Sat Apr 3 13:58:41 2021
InstallationDate: Installed on 2012-01-19 (3362 days ago)
InstallationMedia: Xubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111012)
SourcePackage: lxdm
UpgradeStatus: Upgraded to hirsute on 2021-04-02 (1 days ago)

[Boris Gjenero (boris-gjenero)]

The same problem happens on my main PC (with GeForce GT 710 graphics and 460.56-0ubuntu1 driver). I'm now using sddm instead of lxdm on both systems.

[Boris Gjenero (boris-gjenero)]

The problem seems to be /usr/lib/lxdm/lxdm-greeter-gtk crashing at g_key_file_load_from_file(). Also, lxappearance crashes similarly. This may be related: https://gitlab.gnome.org/GNOME/glib/-/issues/2361 . But the crash seems to be triggered by plasma.desktop and twm.desktop in /usr/share/xsessions. In both of those, the Name[whatever]= and Comment[whatever]= lines cause the crash. Yet xfce.desktop works with such lines.

/usr/lib/lxdm/lxdm-greeter-gdk does work but seems lacking in features.

[Boris Gjenero (boris-gjenero)]

https://bugs.launchpad.net/ubuntu/+source/glib2.0/+bug/1926316 is the bug which is causing this problem. A fix is committed but it hasn't been released yet for 21.04, and apparently has some test failures in the proposed queue. In installed the pre-release files from https://launchpad.net/ubuntu/+source/glib2.0/2.68.1-1~ubuntu21.04.1/+build/21536716 and it fixes the problem

[Chris Guiver (guiverc)]

Thank you for reporting this bug to Ubuntu.

Ubuntu 21.10 (impish) reached end-of-life on July 14, 2022.
Ubuntu 21.04 (hirsute) reached end-of-life on January 20, 2022.

See this document for currently supported Ubuntu releases:
https://wiki.ubuntu.com/Releases

We appreciate that this bug may be old and you might not be interested in discussing it any more. But if you are then please upgrade to the latest Ubuntu version and re-test. If you then find the bug is still present in the newer Ubuntu version, please add a comment here telling us which new version it is in.