Ubuntu - Fail2Ban - Override the default configuration settings

Edit the /etc/fail2ban/jail.d/defaults-debian.conf file, and add configuration changes into the [DEFAULT] section to override.

[DEFAULT]
banaction = nftables
banaction_allports = nftables[type=allports]
backend = systemd
 
[sshd]
enabled = true

WARNING: Do not change entries in the [sshd] section, as that would override settings specifically for the sshd service.

Of course, if there is a need to override settings for the sshd service as well, then go ahead with changes in the sshd section.
- See Override the default configuration settings for the sshd service.

Reload fail2ban to enable the changes.

sudo systemctl reload fail2ban