Find the Process and PID using the Specific port in Ubuntu
Ubuntu is 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.
Now filter the process that using 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.