Linux: Find Out Which Process Is Listening Upon a Port

[ Thanks to An Anonymous Reader for
this link. ]

“How do I find out running processes were associated
with each open port? How do I find out what process has open tcp
port 111 or udp port 7000 under Linux?

“You can the following programs to find out about port numbers
and its associated process:

1. netstat – a command-line tool that displays network
connections, routing tables, and a number of network interface
2. fuser – a command line tool to identify processes using files or
3. lsof – a command line tool to list open files under Linux / UNIX
to report a list of all open files and the processes that opened
4. /proc/$pid/ file system – Under Linux /proc includes a directory
for each running process (including kernel processes) at /proc/PID,
containing information about that process, notably including the
processes name that opened port.”