Hello Nick,

Thanks for your reply.
I am afraid in maintainer provided /etc/fail2ban/jail.conf the backend
setting is already set to auto by default.

$ grep "backend =" /etc/fail2ban/jail.conf
backend = auto
backend = %(sshd_backend)s
#backend = %(syslog_backend)s
backend = %(syslog_backend)s
backend = %(postfix_backend)s
backend = %(syslog_backend)s
backend = %(dovecot_backend)s
backend = %(dovecot_backend)s
backend = %(syslog_backend)s
backend = %(syslog_backend)s
backend = %(syslog_backend)s
backend = %(syslog_backend)s

Can you check what you changed it to, when you have the chance?

On 06/11/2025 14:23, Nick Rickard via Dng wrote:
>
>> 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.
>
>
>
>
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--
With kindest regards, Piotr.