How to Check Port Usage on Linux with lsof, netstat, and a Python Script

Linux Port Inspection

When developing a Python port‑scanning tool, you may need to verify whether specific service ports are already in use on a Linux host.

Using lsof

Run lsof -i:<port> (e.g., lsof -i:8000) to list processes that have opened the given port.

The output shows that port 8000 is occupied by the lightweight file system forwarding service lwfs .

Using netstat

Execute netstat -tunlp | grep <port> (e.g., netstat -tunlp | grep 8000) to display the PID/Program name associated with the port.

The command reveals the process details for port 8000.

Understanding the parameters

The options used in netstat are:

-t : TCP connections

-u : UDP connections

-n : Show numerical addresses

-l : Listening sockets

-p : Show program name/PID

-e : Extended information

Python port‑monitoring script

A ready‑to‑run Python script is provided to check whether a given IP address’s port is occupied.

Running the script produces output similar to the screenshot below, indicating the port status.