Linux/Unix/MacOSX : Find out which application is listening to port 80 or use which IP version

Problem :

You need to find out which Linux/Unix or MacOSX applications are listening to port 80( or any other port numbers ). How to do that?

Solution :

Use the lsof command. lsof stands for list open files - will lists on console(standard output) the file information opened by processes(programs). An open file may be a regular file, a directory, a block special file, a character special file, an executing text reference, a library, a stream or a network file (Internet socket, NFS file or UNIX domain socket.)

For example :

>sudo lsof -i :80

COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME

nginx 1435 root 6u IPv4 10321 0t0 TCP *:http (LISTEN)

nginx 3698 nobody 6u IPv4 10321 0t0 TCP *:http (LISTEN)

From the file descriptor(FD), we can see that the processes use IP version 4. You can filter out lsof command out further, but specifying which sort of information you want to see.

If you want to list out IPv4 only, then use sudo lsof -i4 :80

For IPv6, use sudo lsof -i6 :80