Comment 12 for bug 1993037

Ok. The Ubuntu position is that ubuntu-minimal is the package that defines the smallest system considered Ubuntu. If you don't have ubuntu-minimal installed, you have a pile of packages, but not an Ubuntu system that we can provide support for.

It's impressive that you had a system that has been working continuously without ubuntu-minimal since 2008, I'm glad it's worked for you so far. But the resolution of this bug is that you should install the ubuntu-minimal package.

We will not add additional dependencies on the usrmerge package in an already-released LTS.

Also, if when you say "upgrade from Debian to Ubuntu" you mean cross-grading an existing Debian system, this is not a supported Ubuntu installation path, but if you happen to know whether you followed a cross-grading guide somewhere that fails to mention you should install ubuntu-minimal, I would try to get that guide updated so other users don't trip on such problems.