> I noticed that fail2ban package doesn't work at all on Excalibur.

> fail2ban                [31993]: ERROR   NOK: (38, 'Function not
> implemented')
>  failed!
> invoke-rc.d: initscript fail2ban, action "start" failed.
> dpkg: error processing package fail2ban (--configure):

> Anyone know how to fix this? Thank you.
(I'm afraid this is half an answer as I'm not at the machine in question
at the moment.)

I had a similar issue and traced it to fail2ban defaulting to a systemd
setup. Somewhere in the config files (/etc/fail2ban/jail.conf??) were
lines like:

dovecot_backend = systemd

so fail2ban was trying to initiate the jails using systemd, which
clearly failed on a Devuan system. I can't recall what I changed it to,
possibly "auto", but that hopefully gives you somewhere to start
looking. Upshot is that my fail2ban works in excalibur.