Good day, this is a tracking note of an upstream issue with app-backup/obnam-1.21. It creates 0 file backups for me with gentoo/openrc and one-file-system = true set in the obnam.conf config file. Obnam behaves as expected with 1.19.1. I have a few other gentoo/openrc systems that have simplier fs layouts and do not need this config setting and are not affected.
Wow, this issue report is invalid and fixed upstream. 1.20-1.20.3 were affected while 1.21 is fixed noted at http://git.liw.fi/cgi-bin/cgit/cgit.cgi/obnam/tree/NEWS. Closing.