Does Ubuntu come with a preinstalled or automatic firewall? If not, do I need one?
I've read some articles about the advantages of Linux over other operating systems about security (no need to have antivirus, ...) but would like to be sure.
Ubuntu has a firewall included in the Kernel, and is running by default. What you need to manage this firewall are the iptables. But this are complicated to manage, so you can use UFW (uncomplicated firewall) to configure them. But UFW is still something hard for normal users, so what you can do is install GUFW that is just a graphical front end for UFW.
If you use GUFW, the first time you will see at the bottom of the window 'Disabled Firewall'. But this is not true, your firewall is already running. This enable/disable message refers to the rules set with UFW, not to the firewall.
If you don't believe me open a terminal and write
sudo iptables --list --verbose
Try this with GUFW enabled and disabled. You will see that the only diferences will be the rules you set with GUFW.
Information from this Ubuntu Forums thread
Ubuntu doesn't have a firewall turned on by default in the basic installation.
If you need a firewall, I recommend using gufw to turn it on and manage it:
Gufw is an easy, intuitive, way to manage your Ubuntu firewall, powered by ufw.
It supports common tasks such as allowing or blocking pre-configured services, common P2P, or individual IP/port(s), and many others!
Ubuntu has a firewall called UFW. By default its a command line utility, but there is a gui available -
sudo apt-get install gufw
Once this is installed it can be configured from System -> Administration -> Firewall Configuration.
It should be noted that if your running on a home network behind a router, you router will already be taking care of your firewall concerns.
As a general rule, it is best to only run one firewall at once, so consider switching off your Ubuntu firewall whilst running on your home network.
you need a powerful firewall in Linux use
Firestarter is an Open Source visual firewall program. The software aims to combine ease of use with powerful features, therefore serving both Linux desktop users and system administrators.
We strongly believe that your job is to make the high level security policy decisions and ours is to take care of the underlying details. This is a departure from your typical Linux firewall, which has traditionally required arcane implementation specific knowledge.