Service name database (UNIX)
The /etc/services file contains information regarding the known services available in the DARPA Internet. For each service, a single line should be present with the following information:
official_service_name port_number/protocol_name aliases
The fields are as follows:
Items are separated by any number of blanks, tabs, or both.
The port_number and protocol_name are considered a single item; a / is used to separate the two (e.g. 512/tcp).
A # in a line indicates the beginning of a comment -- any characters after a #, up to the end of the line, aren't interpreted by the routines that search the file.
Service names may contain any printable character other than a field delimiter, newline, or comment character.
getservent() in the Library Reference