Comment 12 for bug 996916

From a comment I left earlier this year on another bug ticket which is now marked as a duplicate:

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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.