How can I check which process is using a specific port on my system?

Why Do You Need to Check Which Process Is Using a Port?

In development, server management, or cybersecurity, you may encounter an issue where a port is already in use—causing services to crash, fail to start, or behave unexpectedly. Whether it's a web server (like Apache or Nginx), a database, or a custom app, knowing which process is binding to a port helps resolve issues quickly.

This guide explains how to identify the process using a specific port in Windows, Linux, and macOS using command-line tools and built-in utilities.

What Is a Port in Networking?

A port is a virtual communication endpoint used by software applications to send or receive data over a network. Ports are numbered (0–65535), and each active network connection on a machine uses a unique combination of IP address + port.

Common examples:

• HTTP uses port 80

• HTTPS uses port 443

• SSH uses port 22

• MySQL uses port 3306

  
  

When two services attempt to use the same port, a port conflict occurs.

How to Check Which Process Is Using a Port in Windows?

Method 1: Using Command Prompt

Step 1: Open Command Prompt as Administrator
Step 2: Run the following command to list all active ports and associated process IDs (PIDs):

netstat -aon | findstr :

Example:

netstat -aon | findstr :8080

You'll get an output like:

TCP    0.0.0.0:8080     0.0.0.0:0       LISTENING       1234

Here, 1234 is the Process ID (PID).

Step 3: To find the name of the process using that PID:

tasklist | findstr 1234

Method 2: Using PowerShell

You can use this in PowerShell:

Get-Process -Id (Get-NetTCPConnection -LocalPort 8080).OwningProcess

How to Check Which Process Is Using a Port in Linux?

Method 1: Using lsof

Step 1: Open Terminal
Step 2: Run the command:

sudo lsof -i :

Example:

sudo lsof -i :8080

Sample output:

COMMAND   PID  USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
java     2345 user   67u  IPv6  12345      0t0  TCP *:http-alt (LISTEN)

This shows that a Java process with PID 2345 is using port 8080.

Method 2: Using netstat

If net-tools is installed:

sudo netstat -tulpn | grep :

Example:

sudo netstat -tulpn | grep :3306

You’ll see something like:

tcp   0  0 0.0.0.0:3306   0.0.0.0:*   LISTEN   4567/mysqld

Method 3: Using ss (modern alternative to netstat)

sudo ss -ltnp | grep :

How to Check Which Process Is Using a Port in macOS?

Method 1: Using lsof

Open Terminal and type:

sudo lsof -i :

Example:

sudo lsof -i :3000

You’ll get output similar to Linux.

Method 2: Using netstat

netstat -anv | grep 

How to Kill the Process Using a Port?

After identifying the PID, you can terminate it manually.

Windows:

taskkill /PID  /F

Example:

taskkill /PID 1234 /F

Linux/macOS:

kill -9 

Example:

sudo kill -9 2345

Use this cautiously—make sure it's safe to kill the process (e.g., not a system-critical service).

Common Use Cases for Port Inspection

Tools That Simplify Port Monitoring

Conclusion: Monitor Ports Proactively

Knowing how to check which process is using a port is a critical troubleshooting skill for developers, sysadmins, and cybersecurity professionals. Whether you're resolving server issues or identifying malicious applications, tools like lsof, netstat, and PowerShell give you the visibility you need.

Understanding and managing port usage not only prevents service failures—it strengthens your system’s overall security posture.

FAQs

How do I find which process is using a specific port on Linux?

You can use sudo lsof -i :PORT_NUMBER or sudo netstat -tulnp | grep PORT_NUMBER to find the process.

What command shows port usage on Windows?

Use netstat -aon | findstr :PORT_NUMBER in Command Prompt, then match the PID with Task Manager.

Is there a GUI tool to check port usage?

Yes, tools like CurrPorts (Windows) or Activity Monitor (macOS) can help.

How can I stop a process using a port in Linux?

Use kill PID or sudo kill -9 PID where PID is the process ID occupying the port.

What does the ss command do?

ss displays socket statistics and is faster than netstat for checking port usage.

Can I check port usage on macOS?

Yes, use lsof -i :PORT_NUMBER or netstat -anv | grep PORT_NUMBER.

Why is port 80 or 443 always in use?

These ports are commonly used by web servers (HTTP/HTTPS), so they may be in use by Apache, Nginx, or similar services.

What if multiple processes show for one port?

It may indicate port sharing or multiple threads from a single application.

Can firewall settings affect port visibility?

Yes, some ports may be filtered or blocked by firewalls, hiding them from standard tools.

Is it safe to close a port in use?

Only if you're certain it won't impact essential services—review the process before terminating it.

What is a PID in port usage?

PID (Process ID) uniquely identifies a process using a system resource like a port.

How do I check UDP port usage?

Use netstat -anu on Linux or include the -p udp flag in ss commands.

Can I use PowerShell to check port usage?

Yes, run Get-Process -Id (Get-NetTCPConnection -LocalPort PORT).OwningProcess.

How to detect port scanning attempts?

Use network monitoring tools like Wireshark or IDS solutions like Snort.

What is a “listening” port?

A port is “listening” if an application is actively waiting for incoming connections.

How to automate port monitoring?

Scripts using lsof, ss, or third-party tools like Nagios can automate port checks.

What does ‘Address already in use’ mean?

This error appears when a port is already bound to another process.

Can malware occupy ports?

Yes, malicious software can open ports to establish backdoors. Regular scanning is essential.

Are there online tools to check open ports?

Yes, websites like canyouseeme.org or yougetsignal.com help test open ports.

How do I free a port on macOS?

Use lsof -i :PORT, then kill the PID shown with kill PID.

What are ephemeral ports?

Temporary ports (usually 49152–65535) used by the OS for client-side connections.

Why use sudo with lsof?

It ensures visibility into processes owned by other users.

Can Docker containers affect host port usage?

Yes, containers can bind to host ports, leading to conflicts.

How to find which app uses a port on Windows?

Use tasklist | findstr PID after identifying the PID from netstat.

What is the -n flag in netstat?

It shows numerical addresses and ports instead of resolving hostnames/services.

Can I check remote port usage?

Only if you have appropriate access—use ssh combined with remote commands.

How to resolve port conflicts permanently?

Reconfigure the application’s port settings or remove conflicting services.

What tool combines all OS port checking?

Nmap can be used across platforms for comprehensive port scans.

Do VPNs affect port visibility?

Yes, VPNs can tunnel or mask ports, making them invisible to local tools.

How to monitor ports in real-time?

Use tools like iftop, nethogs, or system monitoring dashboards.