gnome-shell crashes → unable to log in after artful upgrade

[Paul Natsuo Kishimoto]

CONTEXT

I was running 17.04, and had manually installed gdm3, gnome-shell etc. to use the GNOME Shell. I had also installed some extensions (from both the respositories and through extensions.gnome.org).

I used "sudo do-release-upgrade" to upgrade from 17.04 to 17.10.

$ lsb_release -rd && apt-cache policy gnome-shell
Description: Ubuntu 17.10
Release: 17.10
gnome-shell:
  Installed: 3.26.1-0ubuntu4
  Candidate: 3.26.1-0ubuntu4
  Version table:
 *** 3.26.1-0ubuntu4 500
        500 http://us.archive.ubuntu.com/ubuntu artful/main amd64 Packages
        100 /var/lib/dpkg/status

After rebooting, I tried to install in with all of the available sessions, including:
- GNOME
- GNOME Classic
- GNOME on Xorg
- Ubuntu
- Ubuntu on Xorg

Expected: I'm able to log in to the desktop.
Observed: In every case, I would be kicked back to the GDM greeter.

WORKAROUND

Checking the output of `journalctl`, I noticed the following lines:

Oct 19 15:51:17 khaeru-laptop gnome-shell[30363]: loading default theme (Adwaita)
Oct 19 15:51:17 khaeru-laptop gnome-shell[30363]: Settings schema 'org.gnome.shell.extensions.dash-to-dock' does not contain a key named 'opaque-background'
Oct 19 15:51:17 khaeru-laptop kernel: traps: gnome-shell[30363] trap int3 ip:7f194308c961 sp:7fff78248270 error:0 in libglib-2.0.so.0.5400.1[7f194303c000+111000]
[…more…]
Oct 19 15:51:17 khaeru-laptop polkitd(authority=local)[1189]: Unregistered Authentication Agent for unix-session:20 (system bus name :1.473, object path /org/freedesktop/PolicyKit1/AuthenticationAgent, locale en_CA.UTF-8) (disconnected from bus)
Oct 19 15:51:17 khaeru-laptop gnome-session[30205]: gnome-session-binary[30205]: WARNING: Application 'org.gnome.Shell.desktop' killed by signal 5
Oct 19 15:51:17 khaeru-laptop gnome-session-binary[30205]: WARNING: Application 'org.gnome.Shell.desktop' killed by signal 5

In particular, the complaint about the settings schema always appeared as the last message before the "kernel: traps: gnome-shell" message.

On a hunch, I disabled all extensions:

$ dconf reset /org/gnome/shell/enabled-extensions

After this, I was able to log in.

COMMENT

I understand that my manual installation/use of Gnome Shell prior to the upgrade might have produced some unusual contents in that dconf key. The prior value was:

enabled-extensions=['<email address hidden>', '<email address hidden>', '<email address hidden>', '<email address hidden>', 'suspend-button@laserb', '<email address hidden>', '<email address hidden>']

The bug, IMO, is that this caused gnome-shell to crash that left me unable to log in to any session. If particular extensions or dconf keys are erroneous or broken, I would expect them to be disregarded and perhaps some error message displayed while login continued.

ProblemType: Bug
DistroRelease: Ubuntu 17.10
Package: gnome-shell 3.26.1-0ubuntu4
ProcVersionSignature: Ubuntu 4.13.0-16.19-generic 4.13.4
Uname: Linux 4.13.0-16-generic x86_64
ApportVersion: 2.20.7-0ubuntu3
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Thu Oct 19 16:02:39 2017
DisplayManager: gdm3
EcryptfsInUse: Yes
InstallationDate: Installed on 2017-10-11 (8 days ago)
InstallationMedia: Ubuntu 17.04 "Zesty Zapus" - Release amd64 (20170412)
ProcEnviron:
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_CA.UTF-8
 SHELL=/bin/bash
 LC_PAPER=en_GB.UTF-8
SourcePackage: gnome-shell
UpgradeStatus: Upgraded to artful on 2017-10-19 (0 days ago)

[Daniel van Vugt (vanvugt)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. This particular bug has already been reported and is a duplicate of bug 1719124, so it is being marked as such. Please look at the other bug report to see if there is any missing information that you can provide, or to see if there is a workaround for the bug. Additionally, any further discussion regarding the bug should occur in the other report. Feel free to continue to report any other bugs you may find.