I've been running JRiver for a year or two now on Debian and it works fine. I just upgraded to v31, and now my library is empty. I realize the path is different now and is not pointing to my old library, which is still present.
The path isn't different unless you moved your media files (songs, videos, etc). The issue is that MC for Linux and Mac do not automatically find the MC database from previous versions.
The MC database is what has the locations of all of your songs, their titles, artist names, etc. All of the metadata associated with your media is in the MC database.
The only real way, on Linux and Mac, to get this information back into MC, is to restore a database backup.
File > Library > Restore Library
Otherwise, you would have to start by re-importing your collection again.
A database backup can also (optionally) restore your settings. So all those settings you have tweaked and changed in the last version, can also be ported over to the new version. Just check the box for "settings" when you do your restore.
Brian.