Comment 4 for bug 1663905

I have a simmilar problem with Ubuntu 18.04 too:

Dez 06 21:44:47 systemd[1]: Starting LSB: Radicale CalDAV and CardDAV server...
Dez 06 21:44:47 radicale[24713]: * Starting Radicale CalDAV server radicale
Dez 06 21:44:51 radicale[24713]: Traceback (most recent call last):
Dez 06 21:44:51 radicale[24713]: File "/usr/bin/radicale", line 32, in <module>
Dez 06 21:44:51 radicale[24713]: radicale.__main__.run()
Dez 06 21:44:51 radicale[24713]: File "/usr/lib/python2.7/dist-packages/radicale/__main__.py", line 227, in run
Dez 06 21:44:51 radicale[24713]: "PID file exists: %s" % config.get("server", "pid"))
Dez 06 21:44:51 radicale[24713]: OSError: PID file exists: /var/run/radicale/radicale.pid
Dez 06 21:44:51 radicale[24713]: ...fail!
Dez 06 21:44:51 systemd[1]: Started LSB: Radicale CalDAV and CardDAV server.

Radicale stopped working and I am not able to restart it.