For further clarity, I tried Alexandre's suggestions in #15, but I get different errors:
chdir() to /var/lib/radicale/collections chdir(): No such file or directory [core/uwsgi.c line 3522] ... which is a bald-faced lie. I can ls /var/lib/radicale/collections just fine. I suspect it has something to do with systemd going HAL 9000 on me and not restarting the sockets and services properly because I didn't do it in the right sequence. I'll reboot and see if anything changes.
