Comment 2 for bug 1869410

I think that the problem somehow involves perl being upgraded from 5.22.1 to 5.26 but 5.22.1 still being used when the trigger for doc-base is invoked.

From the dpkg terminal log:

<snip>

Preparing to unpack .../perl_5.26.1-6ubuntu0.3_amd64.deb ...
Unpacking perl (5.26.1-6ubuntu0.3) over (5.22.1-9ubuntu0.6) ...
Selecting previously unselected package perl-modules-5.26.
Preparing to unpack .../perl-modules-5.26_5.26.1-6ubuntu0.3_all.deb ...
Unpacking perl-modules-5.26 (5.26.1-6ubuntu0.3) ...

<snip>

Processing triggers for doc-base (0.10.7) ...
Database error: Cannot read file `/var/lib/doc-base/info/status.yml': Can't locate PerlIO.pm in @INC (you may need to install the PerlIO module) (@INC contains: /etc/perl /usr/local/lib/x86_64-linux-gnu/perl/5.22.1 /usr/local/share/perl/5.22.1 /usr/lib/x86_64-linux-gnu/perl5/5.22 /usr/share/perl5 /usr/lib/x86_64-linux-gnu/perl/5.22 /usr/share/perl/5.22 /usr/local/lib/site_perl /usr/lib/x86_64-linux-gnu/perl-base .) at /usr/share/perl5/YAML/Tiny.pm line 183.
BEGIN failed--compilation aborted.

<snip>

Note that despite the fact that perl 5.22.1 has been replaced with perl 5.26, @INC still contains /usr/share/perl/5.22.1/ .

I have made a pre-upgrade btrfs snapshot. I plan to revert to it then uninstall doc-base and re-run the upgrade, then re-install doc-base. I plan to keep the snapshot if any developer would like me to test upgrade again with a fixed package.