fail2ban not banning IPs on Ubuntu 20.04
Solution 1:
For anyone who finds this a few months after the thread died, I hit the same problem on a new 20.04 server install while following most write-ups.
I solved it by explicitly setting:
sshd_backend = systemd
In my [sshd] section of jails.local.
The default (pynotify) was incorrect for that system or had some deeper issue stopping it from functioning as expected.