Could not install 'gconf2' and upgrade frozen

[Donald Pellegrino]

When performing a distribution upgrade from Ubuntu 16.04.3 xenial to 17.04, a dialog is generated with the following messages:

Could not install 'gconf2'
The upgrade will continue but the 'gconf2' package may not be in a working state. Please consider submitting a bug report about it.
dependency problems - leaving triggers unprocessed

The dialog has a Close button. Clicking it closes the dialog but it then reappears again immediately. It is stuck in a loop.

The distribution upgrade dialog continues in the background for a while. However, it then freeze having last reported "Configuring libpam-systemd (amd64)" in the "Installing the upgrades" step.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: gnome-software 3.20.5-0ubuntu0.16.04.5
ProcVersionSignature: Ubuntu 4.4.0-91.114-generic 4.4.76
Uname: Linux 4.4.0-91-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.10
Architecture: amd64
CurrentDesktop: GNOME
Date: Sat Aug 12 10:54:28 2017
EcryptfsInUse: Yes
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-software
UpgradeStatus: Upgraded to xenial on 2017-08-12 (0 days ago)

[Donald Pellegrino (donald-a-pellegrino)]

This is a critical bug. It led to a path requiring a clean install of Ubuntu and a restore of user data from backups. The upgrade was ultimately unrecoverable even when booting to a Live USB stick to continue the upgrade.

[Launchpad Janitor (janitor)]

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

[Peter Valdemar Mørch (pmorch)]

I've just seen this in a 16.10 -> 17.10 upgrade too. I hit enter i think about 100 times. Eventually the dialog stayed closed.

The upgrade later came with a similar dialog box saying: "Could not install linux-image-4.13.0-39-generic", later similar for "linux-firmware"

In the end it reported: "Could not install the upgrades"/"The upgrade has aborted. Your system could be in an unstable state. A recovery will run now (dpkg-configure -a)". And later: "Upgrade complete"/"The upgrade has completed but there were errors during the upgrade process."

I have a VirtualBox virtual machine snapshot from which this occurred, so I believe this is reproducible from here. I'd be happy to hand it over to a developer if someone wants to have a look at what is occurring. I promise to keep it around two weeks, so until May 20, 2018