If fail2ban won’t start on your Debian system that uses systemd and get the following errors, then edit the ‘backend’ line in your configuration file as shown below:
ERROR failed during configuration: Have not found any log file for sshd jail Async configuration of server failed
If you see the line ‘backend=auto’, change it to:
backend=systemd
Now try to enable fail2ban again:
systemctl enable --now fail2ban