package vanilla-gnome-default-settings 17.10.4 failed to install/upgrade: installed vanilla-gnome-default-settings package post-installation script subprocess returned error exit status 2

[Dylan Taylor]

[Impact]
vanilla-gnome-default-settings will fail to install, if gnome-session has not been configured yet, since that package installs the upstream gdm3 css alternative

Add a Pre-Depends to ensure gnome-session is setup before the postinst script is run.

[Test Case]
On a fresh install of Ubuntu 18.04, install vanilla-gnome-default-settings.
It should not fail processing postinstall script.

[Regression Potential]
Low, we are just ensuring gnome-session is setup before vanilla-gnome-default-settings is installed.

[Launchpad Janitor (janitor)]

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

[ichro furuya (furuya)]

Install Ubuntu 18.04 LTS with the minimum configuration specification.
If you execute the following, an error will occur.

$ sudo apt install vanilla-gnome-desktop
↓
Setting vanilla-gnome-default-settings (17.10.4) ...
update-alternatives: Error: alternative /usr/share/gnome-shell/theme/gnome-shell.css of gdm3.css is not registered. It does not set

In this state, if you execute the following, the error will be resolved.
$ sudo apt install ubuntu-gnome-desktop

---

So, from the beginning,
If you do the following, no error will occur.
$ sudo apt update
$ sudo apt install ubuntu-gnome-desktop
$ sudo apt install vanilla-gnome-desktop

[Tim Lunn (darkxst)]

There is a fix pending for this bug waiting on SRU approval.
https://launchpadlibrarian.net/367853119/ubuntu-gnome-default-settings_18.04.0_source.changes

The recommended workaround in the interim would be:
apt-get install gnome-session
apt-get install vanilla-gnome-desktop
(don't try and combine those two lines, gnome-session package needs to be installed and configured, before vanilla-gnome-desktop)

[Łukasz Zemczak (sil2100)]

This does add a new dependency against gnome-session to vanilla-gnome-desktop - but I guess that's not a problem anyway, accepting the package now. We'll have to make sure to push it into cosmic once the archive is open.

[Łukasz Zemczak (sil2100)]

Hello Dylan, or anyone else affected,

Accepted ubuntu-gnome-default-settings into bionic-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/ubuntu-gnome-default-settings/18.04.0 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-bionic to verification-done-bionic. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-bionic. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

[Tim Lunn (darkxst)]

I have tested the package in proposed and it installs correctly as expected.

vanilla-gnome-desktop has always depended on gnome-session, and vanilla-gnome-default-settings is pretty tightly coupled to vanilla-gnome-desktop, you wouldnt normally install it manually, but rather vanilla-gnome-desktop.

[Launchpad Janitor (janitor)]

This bug was fixed in the package ubuntu-gnome-default-settings - 18.10.0

---------------
ubuntu-gnome-default-settings (18.10.0) cosmic; urgency=medium

  * No-change rebuild for uploading to Cosmic.

 -- Simon Quigley <email address hidden> Sat, 12 May 2018 18:40:11 -0500

[Łukasz Zemczak (sil2100)]

The verification of the Stable Release Update for ubuntu-gnome-default-settings has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.

[Launchpad Janitor (janitor)]

This bug was fixed in the package ubuntu-gnome-default-settings - 18.04.0

---------------
ubuntu-gnome-default-settings (18.04.0) bionic; urgency=medium

  * debian/control: Pre-Depend on gnome-session to ensure the
    gdm alternatives is setup (LP: #1761014)

 -- Tim Lunn <email address hidden> Sun, 29 Apr 2018 12:36:44 +1000

[Hugh Ingram (hughi94)]

I'm affected by this bug, and I am unable to install any packages due to it. Is there something I can do to resolve this, outside of a fresh install?
I'm on a minimal install of 18.04, which was up to date as of 4 days ago.

sudo apt-get -f install
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  gnome-themes-standard libdleyna-core-1.0-3 libgssdp-1.0-3 libgupnp-1.0-4 libmhash2
Use 'sudo apt autoremove' to remove them.
0 to upgrade, 0 to newly install, 0 to remove and 0 not to upgrade.
2 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Setting up gnome-session (3.28.1-0ubuntu3) ...
update-alternatives: error: cannot stat file '/etc/alternatives/gdm3.css': Invalid argument
dpkg: error processing package gnome-session (--configure):
 installed gnome-session package post-installation script subprocess returned error exit status 2
dpkg: dependency problems prevent configuration of ubuntu-gnome-desktop:
 ubuntu-gnome-desktop depends on gnome-session; however:
  Package gnome-session is not configured yet.

dpkg: error processing package ubuntu-gnome-desktop (--configure):
 dependency problems - leaving unconfigured
No apport report written because the error message indicates it's a follow-up error from a previous failure.
                                                                                                            Errors were encountered while processing:
 gnome-session
 ubuntu-gnome-desktop
E: Sub-process /usr/bin/dpkg returned an error code (1)

[Tim Lunn (darkxst)]

Hugh, that is a different bug, please file a new bug for that using `ubuntu-bug gnome-session`.

also you should be installing vanilla-gnome-desktop rather than ubuntu-gnome-desktop (which will transition you to the new ubuntu gnome-shell experience). Although I expect you would still see the same issue

also at a guess maybe installing gdm3 first would help?