Hello,

I noticed that fail2ban package doesn't work at all on Excalibur.
fail2ban is quite important for any publicly exposed service. Just
before upgrading, I had 8549 IPs blocked by fail2ban, attacking my
various exposed services like apache webserver. Now unfortunaly, it
doesn't work, cannot even be installed.

# sudo apt install fail2ban
Installing:
fail2ban

Suggested packages:
monit

Summary:
Upgrading: 0, Installing: 1, Removing: 0, Not Upgrading: 0
Download size: 0 B / 466 kB
Space needed: 2,244 kB / 464 GB available

Selecting previously unselected package fail2ban.
(Reading database ... 374875 files and directories currently installed.)
Preparing to unpack .../fail2ban_1.1.0-8_all.deb ...
Unpacking fail2ban (1.1.0-8) ...
Setting up fail2ban (1.1.0-8) ...
Starting Authentication failure monitor: fail2ban2025-11-05 23:25:05,607 
fail2ban                [31993]: ERROR   NOK: (38, 'Function not 
implemented')
  failed!
invoke-rc.d: initscript fail2ban, action "start" failed.
dpkg: error processing package fail2ban (--configure):
  installed fail2ban package post-installation script subprocess 
returned error exit status 1
Processing triggers for man-db (2.13.1-1) ...
Errors were encountered while processing:
  fail2ban
needrestart is being skipped since dpkg has failed

# dpkg --configure -a
Setting up fail2ban (1.1.0-8) ...
Starting Authentication failure monitor: fail2ban failed!
invoke-rc.d: initscript fail2ban, action "start" failed.
dpkg: error processing package fail2ban (--configure):
installed fail2ban package post-installation script subprocess
returned error exit status 1
Errors were encountered while processing:
fail2ban

apt-cache policy fail2ban
fail2ban:
   Installed: 1.1.0-8
   Candidate: 1.1.0-8
   Version table:
  *** 1.1.0-8 500
         500 http://deb.devuan.org/merged excalibur/main amd64 Packages
         100 /var/lib/dpkg/status

System is AMD64, clean upgrade from Daedalus to Excalibur.
I cleaned /etc/fail2ban/ directory completely, no change.

Anyone know how to fix this? Thank you.

--
With kindest regards, Piotr.