Port 4200 Is Already In Use. Use ‘–Port’ To Specify A Different Port Error

Port 4200 is already in use. Use ‘-port’ to specify a different port error occures sometimes when we run our angular app using ng serve

That means there is another existing service already running on port 4200.

Port 4200 is already in use.Use ‘-port’ to specify a different port error Reasons

1. An existing application(not angular) in your system using the port number 4200. This is a very rare scenario. In this case, you need to change the port number of angular application as mentioned below.
2. You already ran ng serve and to exit the application you typed Control Z (Ctrl+Z), And then you typed ng serve then you will get port 4200 is already in use_ error. In this case, you need to kill the previous process

To close or terminate the angular instance always use Control+C (Ctrl+c)

And ng serve uses default port number 4200 to run the angular application. And our application URL will be http://localhost:4200. To avoid this error we need to change the port number to other port which is free.

According to RFC 793 port numbers is a 16-bit unassigned integer. The minimum value is 0 and the maximum value is 65535.

And, within this range, ports 0 – 1023 are reserved for specific purposes(mostly).

To change the port number for our angular application use the below command

ng serve --port 4201

Now type ng serve

Our angular application will be running on http://localhost:4201

To kill already existing angular process use the below commands

Fix Port 4200 is already in use.Use ‘-port’ to specify a different port error in Mac & Linux

To fix port 4200 is already in use error in In Mac & Linux OS (Ubuntu etc) use the following commands

sudo kill $(sudo lsof -t -i:4200) Or
sudo kill `sudo lsof -t -i:4200` Or
sudo lsof -t -i tcp:4200 | xargs kill -9

Fix Port 4200 is already in use.Use ‘-port’ to specify a different port error in Window

In Window operating system open command prompt. Use the following command to fix port 4200 is already in use error.

netstat -a -n -o | findStr "4200"`

Take the process id and kill the process using the following command

taskkill -f /pid 11128