How to Stop a Process Running on a Specific Port

Reference

Today, I ran into an issue where a process was still occupying a port even after I’d closed the terminal running it. I needed to free up the port (5001 in my case), so I could use it for another service. Now, typically, there are a few straightforward commands that would do the trick, but I didn’t have lsof or netstat installed, which meant finding alternative solutions.

Here’s a rundown of the different methods I explored to stop a process using a specific port, including the fuser command that ultimately saved the day.

Using ss: A Modern Alternative to netstat

The ss command, available on most modern Linux distributions, allows us to view sockets in use on a system. Unlike netstat, ss is faster and doesn’t require separate installation in most cases.

To list processes on a specific port (5001 in this example), I ran:

ss -tuln | grep 5001

Here’s a quick breakdown:

-tuln: This flag combines several options:

• -t for TCP connections.
• -u for UDP connections.
• -l to show listening sockets.
• -n to skip resolving hostnames (for speed).

grep 5001: Filters the output to show only lines containing “5001,” which isolates any connection using that port. Example Output:

tcp LISTEN 0 511 _:5001 _:\*

This output confirmed that something was listening on port 5001. Unfortunately, ss alone doesn’t give us the PID, so I couldn’t kill the process directly with this information.

2. Using lsof: The Classic Option

Typically, lsof (List Open Files) would be my first go-to for finding processes occupying a specific port, as it’s very straightforward:

lsof -i :5001

This command does the following:

• -i :5001: Lists any files (or network sockets) associated with port 5001.

Example Output:

COMMAND   PID USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
myapp    12345 user   3u  IPv4  12345      0t0  TCP *:5001 (LISTEN)

If I’d had lsof, this output would’ve shown the PID (e.g., 12345), and I could have simply run:

kill -9 12345

But since lsof wasn’t installed, I had to find another option.

3. Using netstat: Another Classic (if Available)

Like lsof, netstat is useful but often not pre-installed on modern systems. It can be used similarly to identify ports in use:

netstat -tuln | grep 5001

Explanation:

-tuln options mean the same as with ss, filtering the output to show only listening sockets without resolving hostnames. However, I didn’t have netstat either, so this wasn’t an option.

4. The Winner: fuser to Find and Kill by Port

After trying the above commands, fuser ended up being the lifesaver. The fuser command shows which process IDs (PIDs) are using a specific file or network port. In my case, I used it as follows:

fuser 5001/tcp

Example Output:

5001/tcp:            108371

This output gave me the PID 108371, showing that this process was using port 5001. From there, I ran:

kill -9 108371

This killed the process instantly, and port 5001 was freed up.

Last Words

When a process is occupying a port, several commands (ss, lsof, netstat, and fuser) can be used to identify and stop it. fuser turned out to be my go-to in this case due to limited options, and it worked perfectly. Now, when facing a similar issue, I know that fuser is a reliable option to try if lsof or netstat aren’t available.