Software⏱️ 3 min read📅 2026-06-19

How to Fix: lsof is not working for me on Mac OS X 10.13 - gives error, I'm trying to find process accessing a specific IP address

lsof not working on Mac OS X 10.13, unknown protocol name error

Quick Answer: Check if the IP address is in IPv6 format and try using the '-P' option to specify the protocol

📋 Table of Contents

  1. 🔍 Why This Happens
  2. ✅ Best Solutions to Fix It
  3. ✨ Wrapping Up

The error 'lsof: unknown protocol name (1.2.3.4)' occurs when you try to use the `lsof` command on Mac OS X 10.13 to find a process accessing a specific IP address. This issue affects users who are trying to identify which application or process is using a particular IP address.

This error can be frustrating, especially if you need to troubleshoot network connectivity issues or identify the source of incoming traffic. However, by following the steps outlined in this guide, you should be able to resolve the issue and find the process accessing the specific IP address.

🔍 Why This Happens

  • The primary reason for this error is that `lsof` on Mac OS X 10.13 does not support IPv6 protocol names. The `-i` option only works with IPv4 addresses, which may cause confusion when trying to identify processes using IPv6 addresses.
  • Alternatively, the issue could be due to a misconfigured system or a missing library required by `lsof`. In some cases, the error may also occur if the IP address is not in the correct format or if there are issues with the network configuration.

✅ Best Solutions to Fix It

Using the `-p` Option with IPv4 Addresses

  1. Step 1: Open a Terminal app on your Mac and type `sudo lsof -i :`. Replace `` with the IP address you want to investigate. This will display information about the processes using the specified port.
  2. Step 2: If you want to find the process ID (PID) of the process using the IP address, use the `-t` option instead: `sudo lsof -i : -t`. This will only display the PID of the process.

Using Alternative Tools

  1. Step 1: Alternatively, you can use other tools like `netstat` or `ss` to find the process accessing a specific IP address. For example, `sudo netstat -an | grep ` will display information about the processes using the specified IP address.
  2. Step 2: You can also try using `ss` command: `sudo ss -a | grep `. This will show you all the listening sockets and their corresponding PIDs.

✨ Wrapping Up

To resolve the 'lsof: unknown protocol name' error on Mac OS X 10.13, use the `-p` option with IPv4 addresses or try alternative tools like `netstat` or `ss`. By following these steps, you should be able to identify the process accessing a specific IP address and troubleshoot any network connectivity issues.

Did this fix your problem?

If not, try searching for specific error codes.

🔍 Search Error Database

❓ Frequently Asked Questions

🛠️ Related Fixes

How to Fix: Pc crashes shortly after launching game (rainbow

Fix Pc crashes shortly after launching game (rainbow six siege). Compl

How to Fix: Installing an APK on a locked down phone

Installing an APK on a locked down phone: Try using a rooted device, e

How to Fix: New PC build- no signal and no clue

Fix New PC build- no signal and no clue. Complete troubleshooting guid