Ubuntu prevents upgrading from 15.10 to 16.04

[Stéphane Charette]

Upgrade tells me it cannot upgrade from 15.10 to 16.04 due to one of three possible situations, but it is sorely lacking in details to help users track down the cause of the problem. All I see is the following:

An unresolvable problem occurred while calculating the upgrade.
This can be caused by:
* Upgrading to a pre-release version of Ubuntu
* Running the current pre-release version of Ubuntu
* Unofficial software packages not provided by Ubuntu

I'm relatively certain that cause 1 and cause 2 don't apply. If the problem is due to an unofficial software package, then it should name it or perhaps have a switch to do-release-upgrade to ignore it.

ProblemType: Bug
DistroRelease: Ubuntu 15.10
Package: ubuntu-release-upgrader-core 1:15.10.14.4
ProcVersionSignature: Ubuntu 4.2.0-36.42-generic 4.2.8-ckt8
Uname: Linux 4.2.0-36-generic x86_64
ApportVersion: 2.19.1-0ubuntu5
Architecture: amd64
CrashDB: ubuntu
CurrentDesktop: Unity
Date: Tue May 17 10:17:42 2016
InstallationDate: Installed on 2014-07-07 (679 days ago)
InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140417)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
UpgradeStatus: Upgraded to wily on 2016-05-17 (0 days ago)
mtime.conffile..etc.update.manager.release.upgrades: 2015-08-06T09:39:05

[Stéphane Charette (stephanecharette)]

Finally figured out why upgrades to 16.04 are prevented on many of my computers. The trick is to run this after a failed upgrade:

> cd /var/log/dist-upgrade/
> tail -100 main.log

In my case, this was the problem:

> 2016-06-09 15:48:07,039 DEBUG blacklist expr '^postgresql-.*[0-9]\.[0-9].*' matches 'postgresql-plperl-9.4'
> 2016-06-09 15:48:07,039 DEBUG The package 'postgresql-plperl-9.4' is marked for removal but it's in the removal blacklist
> 2016-06-09 15:48:12,070 ERROR Dist-upgrade failed: 'The package 'postgresql-plperl-9.4' is marked for removal but it is in the removal blacklist.'
> 2016-06-09 15:48:12,071 DEBUG abort called

So the solution for me was to remove that package:

> sudo apt-get remove postgresql-plperl-9.4

However, even knowing this, I still think this bug is valid. The upgrade process should provide more details when the upgrade refuses to run. For example, it could have either shown the name of the offending package, or perhaps even given me the option to remove it so the upgrade can proceed.