React native ERROR Packager can't listen on port 8081

When I run command react-native start, it shows Packager can't listen on port 8081.

I know the issue is about software using my port 8081 .

I use Resource Monitor to see the port, but I can't find 8081, there is no 8081

Can someone show me how to find it?

On a mac, run the following command to find id of the process which is using port 8081
sudo lsof -i :8081
Then run the following to terminate process:
kill -9 23583

Here is how it will look like

You can run the packager on another port.

$ react-native start --port=8088

Alternatively, find out what is using which ports on Windows with netstat.

$ netstat -a -b -o

Netstat gives you a PID, which you can use to kill the process.

$ taskkill /pid 1234

This error is coming because some process is already running on 8081 port. Stop that process and then run your command, it will run your code. For this first list all the process which are using this port by typing

lsof -i :8081  

This command will list the process id (PID) of the process and then kill the node process by using

kill -9 <PID>  

Here PID is the process id of the node process.

That picture indeed shows that your 8081 is not in use. If suggestions above haven't helped, and your mobile device is connected to your computer via usb (and you have Android 5.0 (Lollipop) or above) you could try:

$ adb reconnect

This is not necessary in most cases, but just in case, let's reset your connection with your mobile and restart adb server. Finally:

$ adb reverse tcp:8081 tcp:8081

So, whenever your mobile device tries to access any port 8081 on itself it will be routed to the 8081 port on your PC.

Or, one could try

$ killall node