HOW TO: Install a firewall on Ubuntu
Ubuntu’s desktop install provides a bunch of useful software for desktop users, but it doesn’t install
a firewall by default. Luckily, it’s really simple to get a firewall up and running on Ubuntu.
Frankly, I’m glad that the default install doesn’t set up a firewall. Most of my computers live behind a firewall at all times anyway, and I’ve always been annoyed by installers that demand I deal with firewall questions when I’ve already got the situation well in hand. If I want a firewall on a machine, I can set one up on my own. Since Ubuntu is, in part, aimed at corporate desktops, a firewall is unnecessary for many installations.
But if an Ubuntu desktop is your sole machine that connects directly to the Internet, then it’s a good idea to configure one. Technically speaking, Ubuntu does include a firewall — you could configure everything by hand using iptables. That, however, is a little more detailed than many users care to get. Instead, we’ll look at installing a GUI application to configure a firewall in just a few easy steps. Linux.com | Installing a firewall on Ubuntu