I have tried to tag photos with keywords and tried to add face tags to DigiKam but nothing works. I have DigiKam on my Win 10 laptop and can add tags without issues, but the Ubuntu 16.04 computer I have with DigiKam 5.1 never accepts tags. The message I get is "failed to add tag to database". Up to this point in time, there are no tags in the database at all.
failed to add tag to database ==> file system is read only ? It work perfectly here... Gilles Caulier
I decided that since I had upgraded DigiKam from 4.22 to 5.0 then to 5.1, the problem was probably in the database. So I found the DigiKam database in my Pictures folder and deleted it, then got Digikam to create a new database. Now the tags work like they're supposed to.