problems upgrading from 14.04 to 16.04

[Ralf Mardorf]

On Wed, 28 Sep 2016 18:42:28 +0200, Oliver Grawert wrote:
>Am Mittwoch, den 28.09.2016, 18:18 +0200 schrieb Ralf Mardorf:
>> > My apologies :D, wrong package. To be continued...  
>> Ok, this is the correction, so from where exactly is gcc-5-base
>> 5.4.1-2ubuntu1~14.04?  
>
>from the toolchain PPA most likely, i think that is the only place
>where a gcc5 for trusty exist at all ...

I know this, but seemingly the OP doesn't know. A PPA, proposed
etc. aren't official repositories. If a package that isn't shown by
http://packages.ubuntu.com/ does cause nearly unresolvable conflicts,
then it easily could happen, that user-friendly tools, such as "apt
--fix-broken" can't resolve such issues. The user needs to maintain it
and it could simply be much work, that requires to remove many packages
that aren't existentially first, before it might be possible to fix the
issue and to reinstall packages. Fooling the package management would be
possible too, but this requires much knowledge and is much work, too,
let alone that it easily could screw up the install completely.
Hopefully the OP made/makes backups of the complete install.

Btw. if a backup of 14.04 should be available, I would restore 14.04
and before upgrading to 16.04 again, remove non-official packages.

Regards,
Ralf