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micahwierenga/port_already_in_use.md

Last active February 20, 2020 20:49
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port_already_in_use.md

When a port is already in use

Sometimes, when running nodemon or node server.js, you'll trigger one of the following errors:

Error: listen EADDRINUSE: address already in use :::3000

or

Port 3000 is already in use
[nodemon] app crashed - waiting for file changes before starting...

This usually means that either you have an app running on port 3000 in another terminal, or you closed your terminal without shutting down your server (ctrl + c).

In order to resolve this in Linux, begin by using this command:

lsof -i tcp:3000

This will return some info about any processes running on the port that follows tcp::

COMMAND  PID          USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
node    3870 micahwierenga   23u  IPv6 0xac33fe12a5a6a54d      0t0  TCP *:hbci (LISTEN)

The piece that we want to pay attention to is the PID (or Process ID). Take that number (if you have multiple rows, take the PID from the first row) and use it in the following command:

kill -9 3870

You will, of course, replace 3870 with the PID that is returned in your terminal.

This should stop that process so that you can start a new process (e.g., nodemon or node server.js on port 3000) on that port.

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