02 Configure firewall.md

BEWARE THAT YOU SHOULD AT LEAST HAVE CONSOLE ACCESS TO YOUR SYSTEM BEFORE EXECUTING THE INSTRUCTIONS BELOW!!!

Installing a firewall

To stay safe, it is mandatory to install a firewall. Here we are going to use ufw firewall.

Install ufw with the following command

sudo apt install ufw

sudo ufw status

Configuring the firewall

We will initially set up the firewall that is only accepts ssh incoming sessions. There has to be an exception made in the firewall for each service we configure.

sudo ufw allow ssh/tcp
sudo ufw limit ssh/tcp
sudo ufw logging medium
sudo ufw enable

After configuring the firewall, you can check it with

sudo ufw status

Note that you can always disable the firewall with:

sudo ufw disable

Adding exceptions for services

Each new service port has to be added with a command similar like:

ufw allow 9387/tcp

Removing firewall rules

To remove rules from the firewall use:

sudo ufw status numbered
sudo ufw delete 2