This question already has an answer here:
Do I need to activate the firewall? I only use Ubuntu for a home desktop use? 1 answer
When I first touched linux, I installed Zorin. It's essentially an Ubuntu fork, but the desktop is redesigned to make it look like home to a person who has been using Windows for a long time. It came with a firewall pre-installed. A few months ago I decided that some answers to questions here were pretty incompatible with Zorin (especially using the dash, as it does not exist there). The installation was also generally pretty broken.
I just noticed that Ubuntu doesn't seem to come with a firewall pre-installed. I am, unlike this one, pretty much a geek and I will likely have not much trouble setting it up. My question is, is it a better idea to install that firewall for this system, or leave it alone? Because it seems to not come with a firewall, but maybe there's one running in the background, where I cannot see it.
This question is also not exactly a duplicate of this one, that one doesn't know if they need one, I already know I need one, but I am not sure if I need to install one or if there's already one running in the background.
No, there's no firewall pre-installed. It's only needed when you are opening up some ports to the outside internet, such as for hosting a server (especially for hosting webservers), using remote desktop, or things like that. Stuff like skype uses ports but it won't really create the need for a firewall.
If you need one: Ufw is a simple good firewall. You can install it with this command:
sudo apt-get install ufw
To start it, run this one (make sure you ran the above command as well):
sudo ufw enable
If you're not such a geek, but still want to have a firewall running, use this one instead,
sudo apt-get install gufw
This will install ufw, and the graphical user interface (GUI) that you can control ufw with. You do not need to install ufw first if you install this.
After that, you can start configuring ufw by running this command in a terminal:
To start right away, just click the enable switch. You may want to add some firewall rules for programs that you use. Refer to the FAQ of any program that you think is waiting for incoming connections, at any time, even briefly. These are especially instant message (IM) programs, such as Skype, Steam, remote desktop servers, or things like that.