hosts - host name data base
The hosts(5) file contains information regarding the known hosts on the network. For each host, a single line should be present with the following information:
official host name
Internet address
aliases
Items are separated by any number of blanks, tab characters, or both. A pound sign (#) indicates the beginning of a comment; characters up to the end of the line are not interpreted by routines that search the file.
When using the name server named(1), this file provides a backup when the name server is not running. For the name server, it is suggested that only a few addresses be included in this file.
This file can be created from the official host data base maintained at the Network Information Center. Local changes can be required to bring it up to date regarding unofficial aliases and unknown hosts, however. As the database maintained at the Network Information Center is incomplete, it is recommended that you use a name server for sites on the Internet.
Network addresses are specified in the conventional dot (.) notation using the inet_addr(3) routine from the Internet address manipulation library, inet(3). Host names can contain any printable character other than a field delimiter, newline, or comment character.