[olesen]

A few people have reported an odd issue with finding libmpi.so on various Ubuntu installations, but strangely enough, not on a docker image of Ubuntu. Some details of the detective work can be found here: https://develop.openfoam.com/Develop.../-/issues/1817
The summary is that the installation triggers for libopenmpi-dev might be run too soon and it fails to properly create a symbolic link for libmpi.so to the underlying library (eg, to libmpi.so.40.20.3)
If this occurs, there will be problems compiling Pstream with the message that -lmpi cannot be found.
One remedy (might be a bit heavy-handed) is to forcibly reinstall the libopenmpi-dev. When doing so, we wish to not remove/reinstall any other packages.

$ sudo dpkg --remove --force-all libopenmpi-dev
$ sudo apt install libopenmpi-dev

Would be happy if there was a nicer way to do this, but it seems to solve things.
If you don't want to bother with compiling from source, just one one of the precompiled packages instead
https://develop.openfoam.com/Develop...ompiled/debian