How to tell to fail2ban what init system are you running

I owed myself a fail2ban installation on the Raspberry Pi. A simple view of this log tell you many things:

Jun 17 07:54:15 raspberrypi systemd[1]: Starting Fail2Ban Service...
Jun 17 07:54:28 raspberrypi fail2ban-client[11687]: ERROR No file(s) found for glob /var/log/proftpd/proftpd.log
Jun 17 07:54:28 raspberrypi fail2ban-client[11687]: ERROR Failed during configuration: Have not found any log file for proftpd jail
Jun 17 07:54:29 raspberrypi systemd[1]: fail2ban.service: Control process exited, code=exited status=255
Jun 17 07:54:29 raspberrypi systemd[1]: Failed to start Fail2Ban Service.
Jun 17 07:54:29 raspberrypi systemd[1]: fail2ban.service: Unit entered failed state.
Jun 17 07:54:29 raspberrypi systemd[1]: fail2ban.service: Failed with result 'exit-code'.
Jun 17 07:54:29 raspberrypi systemd[1]: fail2ban.service: Service hold-off time over, scheduling restart.
Jun 17 07:54:29 raspberrypi systemd[1]: Stopped Fail2Ban Service.
Jun 17 07:54:29 raspberrypi systemd[1]: Starting Fail2Ban Service...

You may notice I’ve tried to start up Fail2ban unsuccesfully. So let’s debug…
It appears an error that informs there’s no proftd.log. The second line points to the same log file, but related with fail2ban configuration (jail, here means fail2ban configuration).

After digging a lit bit I’ve found that fail2ban sets as auto its configuration and try to guess if your system is managed by systemd, traditional systemV init scripts or whatever. I edit the /etc/fail2ban/jail.conf, I set backend = systemd and fail2ban starts up succesfully.