Gufw Firewall

https://help.ubuntu.com/community/UFW
Enable and Disable
Enable UFW
To turn UFW on with the default set of rules:
    sudo ufw enable
To check the status of UFW:
    sudo ufw status verbose
The output should be like this:
youruser@yourcomputer:~$ sudo ufw status verbose
[sudo] password for youruser:
Status: active
Logging: on (low)
Default: deny (incoming), allow (outgoing)
New profiles: skip
youruser@yourcomputer:~$
Note that by default, deny is being applied to incoming. There are exceptions, which can be found in the output of this command:
    sudo ufw show raw
You can also read the rules files in /etc/ufw (the files whose names end with .rules).
Disable UFW
To disable ufw use:
    sudo ufw disable