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Something is already running on port 3000

equuscaballus profile image equuscaballus ・1 min read

Hi Everyone
I have downloaded a few react project from github for study purpose. When I run the project with the command npm start I got this error message : "Something is already running on port 3000".

Now I if I restart the PC then I can run the project again. How can I run the projects without restarting the PC ? What's the solution ?

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aledileo profile image
Alejandro Di Leo

Hi! Are you trying to run those few projects at the same time? If that's the case, it's possible that by default they will try to use that same port. Normally you can set PORT as an env variable to tell the project to run that specified port (this depends on the server being used). You can try running PORT=3001 npm start (or an equivalent to set env variables per command in your OS), changing the port value for each project

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equuscaballus profile image
equuscaballus Author

Hi

Thanks for the reply. Actually now while running the project if I change the port number then it runs !

Thank you for your help :)

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equuscaballus profile image
equuscaballus Author

I was wondering if there is any way to define the port number in the source code ? For example if I want to set a different port number for different project ?

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aledileo profile image
Alejandro Di Leo

It really depends on the server and implementation being used. For example if the project is using create-react-app, you can create a .env file with all your project based env variables. This is because create-react-app uses dotenv. If you can find this out or you're able to share the github repo I may be able to assist further

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equuscaballus profile image
equuscaballus Author

I just downloaded the projects form github randomly. couldn't find the repository URL. Do you know in which file of the source code the port number is defined ?

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aledileo profile image
Alejandro Di Leo

That also depends on the server being used. You can check the package.json file for more info, for example the scripts part. What is the value for the start command?

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equuscaballus Author

I will check that . you are very helpful . Thanks a lot :)

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ekeijl profile image
Edwin

Sometimes the Node process just hangs and you need to stop it manually.
Enter this into your terminal if you want to check if something is still running at that port:

lsof -i :3000

Then you can stop the process in your terminal if you want.

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equuscaballus profile image
equuscaballus Author

tried that command but didn't worked

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alekseiberezkin profile image
Aleksei Berezkin

Hi! I used to encounter this error. It may happen if you close the editor or console with running node — sometimes editor doesn't close it. You may use your console or process explorer to find it and forcibly stop freeing the port.

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myogeshchavan97 profile image
Yogesh Chavan

You can simply execute npx kill-port 3000 to kill the process which is using port 3000