How to find which process is using a particular port on Ubuntu

There are situations in which we will get this error message.

the port is already in use 

This occurs when we are trying to install or execute something, and after some searching I found the following commands, to find the process which uses a particular port. I am adding the commands to kill that (if required), most of the time I do so.

So open a terminal window by pressing ctrl + alt + t .

These are the commands to find which process is using port 3000 .

$ sudo netstat -tulpn | grep 3000

Netstat is a command-line tool that displays network connections for the Transmission Control Protocol, routing tables, and a number of network interface and network protocol statistics.

The above command may ask you for administrator password. It gave me this output.

	
$ sudo netstat -tulpn | grep 3000	
	
tcp        0      0 0.0.0.0:3000            0.0.0.0:*               LISTEN      19911/node

The options used with netstat are:

	t : Display tcp connections.
	u : Display udp connections.
	p : Display the process using the socket.
	n : Display the addresses and ports in numeric form.

A node server script is running with PID 19911 , to kill that I use :

$ sudo kill 19911 

So port 3000 on my system is free now :)