This comprehensive Linux guide expects that you run the following commands as root user but if you decide to run the commands as a different user then ensure that the user has sudo access and that you precede each of the privileged commands with sudo

A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predetermined security rules. A firewall typically establishes a barrier between a trusted internal network and untrusted external network, such as the Internet.

The firewall is suggested to be kept enabled on your system, but in some cases, you might need to disable it. This tutorial will guide you how to disable/enable your firewall on your Ubuntu 18.04.

Checking Your Firewall Status

To check whether your firewall is enabled or disabled, you can run the following command:

root@codesposts:~$ ufw status

Status: active

This shows that the firewall is enabled.

If you want more verbose output of the status of the firewall, you can use the command like below: 

root@codesposts:~$ ufw status verbose

Disabling The Firewall

You can disable the firewall by running the following command

root@codesposts:~$ ufw disable

Firewall stopped and disabled on system startup

Resetting Firewall Rules

If you disable the firewall using the above command, the firewall will be disabled but the rules will not be deleted. If you want to delete those firewall rules too, you can reset the firewall by running the following command

root@codesposts:~$ ufw reset

Resetting all rules to installed defaults. This may disrupt existing ssh
connections. Proceed with operation (y|n)? y
Backing up 'user.rules' to '/etc/ufw/user.rules.20190122_115214'
Backing up 'before.rules' to '/etc/ufw/before.rules.20190122_115214'
Backing up 'after.rules' to '/etc/ufw/after.rules.20190122_115214'
Backing up 'user6.rules' to '/etc/ufw/user6.rules.20190122_115214'
Backing up 'before6.rules' to '/etc/ufw/before6.rules.20190122_115214'
Backing up 'after6.rules' to '/etc/ufw/after6.rules.20190122_115214'

Enabling The Firewall

If your firewall is disabled, you can run the following command to enable it:

root@codesposts:~$ ufw enable

Command may disrupt existing ssh connections. Proceed with operation (y|n)?y
Firewall is active and enabled on system startup