How to kill a process on a port on ubuntu/Mac/Linux

Best way do that:
To kill a Process running on port number 9001
sudo kill -9 $(sudo lsof -t -i:9001)

lsof - list of files(Also used for to list related processes)

-t - show only process ID

-i - show only internet connections related process

:9001 - show only processes in this port number

kill - command to kill the process
-9 - forcefully
sudo - command to ask admin privilege(user id and password).

More:15 Linux lsof Command Examples