hosts(4)																  hosts(4)

NAME

       hosts - host name database

SYNOPSIS

       /etc/inet/hosts

       /etc/hosts

       The  hosts  file  is a local database that associates the names of hosts with their Internet Protocol (IP) addresses. The hosts file can be
       used in conjunction with, or instead of, other hosts databases, including the Domain Name System (DNS), the NIS hosts map, the  NIS+  hosts
       table, or information from an LDAP server. Programs use library interfaces to access information in the hosts file.

       The  hosts file has one entry for each IP address of each host. If a host has more than one IP address, it will have one entry for each, on
       consecutive lines. The format of each line is:

	      IP-address official-host-name nicknames...

       Items are separated by any number of SPACE and/or TAB characters. The first item on a line is the host's IP address. The  second  entry	is
       the  host's  official  name.  Subsequent entries on the same line are alternative names for the same machine, or "nicknames." Nicknames are
       optional.

       For a host with more than one IP address, consecutive entries for these addresses may contain the same or  differing  nicknames.  Different
       nicknames are useful for assigning distinct names to different addresses.

       A  call	to gethostbyname(3NSL) returns a hostent structure containing the union of all addresses and nicknames from each line containing a
       matching official name or nickname.

       A `#' indicates the beginning of a comment; characters up to the end of the line are not interpreted by routines that search the file.

       Network addresses are written in the conventional "decimal dot" notation and interpreted using the  inet_addr  routine  from  the  Internet
       address manipulation library, inet(3SOCKET).

       This interface supports host names as defined in Internet RFC 952 which states:

	      A  "name"  (Net,	Host,  Gateway,  or Domain name) is a text string up to 24 characters drawn from the alphabet (A-Z), digits (0-9),
	      minus sign (-), and period (.). Note that periods are only allowed when they serve to delimit components of  "domain  style  names".
	      (See RFC 921, "Domain Name System Implementation Schedule," for background). No blank or space characters are permitted as part of a
	      name. No distinction is made between uppercase and lowercase. The first character must be an alpha character [or a digit. (RFC  1123
	      relaxed  RFC  952's  limitation  of  the	first character to only alpha characters.)] The last character must not be a minus sign or
	      period.

       Host names must not consist of numbers only. A host name must contain at least one alphabetical or special character.

       Although the interface accepts host names longer than 24 characters for the host portion (exclusive  of	the  domain  component),  choosing
       names for hosts that adhere to the 24 character restriction will insure maximum interoperability on the Internet.

       A  host which serves as a GATEWAY should have "-GATEWAY" or "-GW" as part of its name. Hosts which do not serve as Internet gateways should
       not use "-GATEWAY" and "-GW" as part of their names. A host which is a TAC should have "-TAC" as the last part of its host name, if it is a
       DoD host. Single character names or nicknames are not allowed.

       Example 1: Example of a typical line from the hosts file.

       Here is a typical line from the hosts file:

       192.9.1.20	 gaia			     # John Smith

       gethostbyname(3NSL), inet(3SOCKET), nsswitch.conf(4), resolv.conf(4)

       /etc/inet/hosts is the official SVR4 name of the hosts file. The symbolic link /etc/hosts exists for BSD compatibility.

								    30 Sep 2005 							  hosts(4)