There is a great terminal software package called nmap that you can launch to get a readout of open ports etc. on a target machine on your local or Internet.
With the addition of the GUI (graphical user interface) Zenmap, this tool is even easier to use!
Head to your Software Manager and search for Zenmap. This is the GUI, but will also install the dependency nmap as well.
Running it on your localhost can show you open ports you might not be aware of, or show you how well your firewall software is running. (You do run a firewall right?)
Running against my Android phone, I was quite happy to find no open ports, and the phone rejected attempts to get any useful data from it.
You can check your entire network at once, by typing your local network in the Target box like this: Target: 192.168.1.* (or however your network is set up. In my case, Target: 10.1.0.* ) The * variable is an easy way to force a check of everything the scanner can find. While *.*.*.* will indeed work, we don’t recommend it!
One of my favorite features is the ability for Zenmap to map out your entire network, as shown in the example below:
Zenmap can help you find those open ports in networked computers that you might want to shut down, or even find machines on your network you didn’t even know were there!