How To Spot Open Ports in Linux

Hey there! Today, I’ll walk you through the process of finding open ports on your Linux system.

First things first, let’s establish what open ports are. Think of a port as a virtual gateway that allows communication between different software applications. Just like a door or a window, a port can be open or closed. Open ports are like open doors, allowing data to flow in and out freely.

Now, onto the exciting part – checking for open ports! You and I are going to unleash some powerful commands to get this job done. So buckle up!

To begin, let’s open up the Terminal. You can find it by searching in the applications menu or by pressing Ctrl+Alt+T on your keyboard.

Once the Terminal is open, we’ll use a command called netstat to display active network connections. It’s like peeking into the virtual world of communication.

Type in the following command and hit Enter:

netstat -an

Whoa! Look at all that information flooding your screen. Don’t worry, I’ve got your back. We’ll take it step by step.

The results will show you a list of connections, including the Local Address and Foreign Address. These addresses consist of an IP address and a port number, separated by a colon.

Now, imagine you want to filter this list and only see open ports. Super simple! Just add a handy option called -l to the command.

Use this command instead and press Enter:

netstat -anl

Voila! The list now only displays open ports. You’ve successfully filtered out the closed ones. You’re crushing it!

But wait, there’s more! I’ve got another ace up my sleeve. The -p option allows us to see which application is listening on each open port.

Try this command and hit Enter:

netstat -anlp

Boom! Now you can see the applications associated with the open ports. It’s like giving those hidden doors a name.

You’re officially a detective of the virtual world, my friend. With the power of these commands, you can uncover open ports like a pro.

Remember, open ports can leave your system vulnerable to unwanted access. So, always stay vigilant and ensure that only the necessary ports are open.

Now go forth and explore the vast realm of open ports with confidence!

‘I’m new to Linux and someone told me to check for open ports on my Linux box to ensure security. What exactly does that mean, and should I actually do it?’ This question was sent to us by a curious TechJunkie reader, and I find it intriguing enough that others would likely be interested as well.

Since ports play a crucial role in how a computer connects to the internet, it’s a fascinating subject to delve into.

What’s the deal with ports?

So, let’s talk about ports. They can be physical or virtual. A physical port is like the Ethernet port on your computer or the LAN or WAN ports on your router. But for this discussion, we’re focusing on virtual ports on your computer, which are a bit different from the physical ones.

Basically, a port is like a virtual gateway into your computer that specific services use. You know, services like email, web browsing, streaming, file transfer, and remote access. Each of these services has been assigned a different port number, so your computer and its applications know what’s what.

Let me give you an example. When something lands on port 80, it’s HTTP or web traffic. Port 443 is for secure web traffic, or HTTPS. And if it arrives on port 25, it’s SMTP, or email traffic. There are actually more than a thousand different port assignments, even though there aren’t that many web services. Crazy, right?

Here’s another example. When you connect to TechJunkie with your browser, it uses port 443 to let the web server know you’re asking for the secure version of the page. And if I wanted to upload files to the server, I would use FTP ports 989 or 990 for secure FTP. When the request arrives on those ports, the server immediately knows what kind of traffic it is and sends it to the right place.

Routers also have ports, but they’re a different story and not really our focus here.

What’s the deal with open and closed ports?

So, here’s the thing. The terms “open” and “closed” when it comes to ports are actually not quite right. Ports are either filtered or unfiltered. See, a firewall can “block” ports by not letting applications communicate through them. Or, it can let all traffic through, depending on the settings. But even if a port is blocked, it’s still technically open. An application may still be waiting for traffic on that port, but the firewall just blocks any unauthorized traffic from getting through.

Now, most common ports are automatically left unfiltered by your firewall. It’s programmed to allow traffic through these ports unless you specifically tell it not to. So, when you use a firewall to block internet access, you’re basically telling it to block and drop any traffic heading to port 80 or port 443.

Let’s Check Ports in Linux

Hey there! So, you’ve got a bunch of tools at your disposal in Linux to figure out what’s happening. Checking ports is pretty straightforward, but it’s up to you how deep you want to dive into understanding your Linux device.

One of the go-to commands for checking ports and other network services in Linux is Netstat.

• Just open up a terminal and type ‘netstat -atu’ and hit Enter. This will show you all the sockets, TCP, and UDP connections that are currently active in Linux.
• If you just want to see the ports that are actively listening on your computer, you can type ‘netstat –listen’ or ‘netstat -l’ and hit Enter.
• For a list of existing TCP connections from your computer, type ‘netstat -vatn’ and hit Enter.
• If you’re interested in existing UDP connections, simply type ‘netstat -vaun’ and hit Enter.
• Want to know which program is listening to each port? Type ‘netstat -ltup’ and you’ll see all the connections along with the associated program.
• And if you want to see the IP addresses along with the port numbers, just type ‘netstat -lntup’ and hit Enter.

These commands might seem similar, but they offer different information based on what you need. However, each one will answer the original question.

But Can You Actually ‘Close’ Ports?

Okay, so here’s the thing. When someone tells you to ‘close’ a port, they mean filtering it. But the truth is, you can’t physically close a port on your Linux computer. The only way to do it is by stopping the program that’s listening on that port or filtering it using your firewall.

Now, if you’re an advanced user, you can experiment with IPTables in certain Linux distributions, but honestly, that’s a bit too complicated for me. Luckily, there’s a guide that can walk you through it if you’re interested.

So, Do You Really Need to Check Ports?

If you have a firewall and practice good internet hygiene, chances are you won’t really need to check for ports on your Linux computer. For desktop users, ports aren’t a major concern. However, if you’re managing a Linux server, web server, or router, ports become much more important. In any case, a solid firewall should take care of everything for you.