Both root and calibreweb are users by default. I've added other users and groups, but still no love.
I've updated the config file to include "_library="media/Books"....no love either, even though my db file and books are in that location.
I even changed the local host from 127.0.0.1 to 0.0.0.0...was a long shot...no love either.
I still get same DB error above.
-----
Mountpoint:
/mnt/Files/Data/Books
/mnt/Media/iocage/jails/calibre-web/root/media/Books