Ubuntu – add-apt-repository missing from mini.iso

They're the same command, someone just added the inverse because people kept mixing the command up and typing it wrong.

Ok. Thanks to Thomas W. for comments that led me to the solution.

The cause seems to trace back to broken packages. I had previously searched how to fix broken packages, but none of the solutions fixed the whole problem. I searched instead for the Hash Sum mismatch error I was getting at the end of apt-get update, and found this solution, that solved the problem.

Answer copied here for completeness:

Remove the content of /var/lib/apt/lists directory:

sudo rm -fR /var/lib/apt/lists/*

then run:

sudo apt-get update

Apparently, and you gurus can correct or elaborate, the clean and autoclean flags for apt-get didn't completely purge the problem children from apt/lists directory.