Getting stuck on errors like "Address already in Use"?

Problem

It is quite common that some ghost processes remain hold of certain ports. The ports may be intentionally or unintensionally blocked.

Commonly used ports such as 3000, 5000 etc. are often gets blocked by node/python processes.

Solution

Open a terminal and do the following for one time usage.

• Freeing up a single port. Eg. Port 3000 in this case.

kill -9 $(lsof -ti:3000)

• Freeing up multiple ports. Eg. Port 3000 and 3001 in this case.

kill -9 $(lsof -ti:3000,3001)

For Linux/Ubuntu systems:

sudo kill -9 `sudo lsof -t -i:3000`

To do this every time when a node server starts up.

Add to package.json file as follows

"scripts": {
   "start": "kill -9 $(lsof -ti:3000,3001) && npm start"
}

Explanation

lsof -ti:3000 command return the PID (Process ID) of the process which is using the port. kill -9 command kills the process with the returned PID.