Linux See Bandwidth Usage Per Process With Nethogs Tool

Originally published at: https://www.cyberciti.biz/faq/linux-find-out-what-process-is-using-bandwidth/

I have Red Hat Enterprise Linux 6.x/7.x server. How do I find out and groups network bandwidth usage by process under Linux operating systems? How do I know what programs are using network bandwidth under Linux operating systems? How can I see bandwidth usage per PID, command, and user on a Linux operating systems?