The previous panel mentioned that inetd classifies incoming connections based on type. Each incoming connection includes some identification fields in the TCP/IP header. The fields that interest us the most are source address, destination address, protocol, and port number. Incoming connections are classified by inetd based on port number and protocol (usually TCP or UDP, see /etc/protocols for the complete list of services that can be serviced by inetd).

Each line has the format:

service-name  port-number/protocol-name  aliases   # comment

For example, let's investigate the top few entries:

# grep ^[^#] /etc/services | head -5
tcpmux    1/tcp              # TCP port service multiplexer
echo      7/tcp
echo      7/udp
discard   9/tcp   sink null
discard   9/udp   sink null

In general, /etc/services already contains all the useful service names and ports. If you wish to add your own, you should first consult the list of assigned port numbers.