Sometimes you want to know what applications are taking up the ports on your computer, a useful terminal cli too is lsof.

In the terminal, get instruction information by running man lsof. You may get the following information depending on your computer environment.

Lsof revision 4.91 lists on its standard output file information about files opened by processes for the following UNIX dialects:

Apple Darwin 9 and Mac OS X 10.[567]
FreeBSD 8.[234], 9.0 and 1[012].0 for AMD64-based systems    Linux 2.1.72 and above for x86-based systems
Solaris 9, 10 and 11

(See the DISTRIBUTION section of this manual page for information on how to obtain the latest lsof revision.)

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.) A specific file or all the files in a file system may be selected by path.

Instead of a formatted display, lsof will produce output that can be parsed by other programs. See the -F, option description, and the OUTPUT FOR OTHER PROGRAMS section for more information.

In addition to producing a single output list, lsof will run in repeat mode. In repeat mode it will produce output, delay, then repeat the output operation until stopped with an interrupt or quit signal. See the +|-r [t[m]] option description for more information.

To find out what is listing on just the TCP ports -

lsof -P -iTCP -sTCP:LISTEN