Find the Process and PID using the Specific port in Ubuntu

Ubuntu is a Linux Operating System so you need to have Root privilege to get the process information.

netstat command is used to show the ports and processes in Linux. 

netstat -nlp command is used to show the processes using network.

netstat -nlp

Now filter the process that using a specific port.

netstat -nlp|grep 3000

(Not all processes could be identified, non-owned process info

 will not be shown, you would have to be root to see it all.)

tcp        0      0 0.0.0.0:3000            0.0.0.0:*               LISTEN      16698/node      

Here 16698 is the PID and node is the process.