$ sudo ufw enable            # Turn the firewall on
$ sudo ufw disable           # Turn it off
$ sudo ufw status             # Show current rules

$ sudo ufw allow in on enx6c1ff76c1d75 to any port 2049 proto tcp # specific interface
$ sudo ufw deny in to any port 2049 # deny otherwise

$ sudo ufw reload
$ sudo ufw status verbose # list rules

$ sudo ufw allow ssh          # Allow SSH (port 22)
$ sudo ufw allow 80           # Allow HTTP
$ sudo ufw deny 23            # Block Telnet
$ sudo ufw delete allow 80    # Remove a rule

$ sudo ufw status verbose # check logs level
$ sudo ufw logging on

$ sudo ufw logging low    # default, least verbose
$ sudo ufw logging medium
$ sudo ufw logging high
$ sudo ufw logging full  # very verbose

$ sudo less /var/log/ufw.log
or
$ sudo tail -f /var/log/ufw.log # real time

$ sudo grep "BLOCK" /var/log/ufw.log # blocked traffic