services – Internet network services list 

cat /etc/services

services is a plain ASCII file providing a mapping between friendly textual names for internet services, and their underlying assigned port numbers and protocol types. Every networking program should look into this file to get the port number (and protocol) for its service.

A sample services file might look like this:

netstat         15/tcp
qotd            17/tcp          quote
msp             18/tcp          # message send protocol
msp             18/udp          # message send protocol
chargen         19/tcp          ttytst source
chargen         19/udp          ttytst source
ftp             21/tcp
# 22 - unassigned
telnet          23/tcp