hosts(4)							   File Formats 							  hosts(4)

NAME

       hosts - host name database

SYNOPSIS

       /etc/inet/hosts

       /etc/hosts

       /etc/inet/ipnodes

DESCRIPTION

       The  hosts file is a local database that associates the names of hosts with their Internet Protocol (IP) addresses. An IP address can be in
       either IPv4 or IPv6 format. 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 infor-
       mation in the hosts file.

       Note that /etc/hosts and /etc/inet/ipnodes are symbolic links to /etc/inet/hosts.

       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 IPv4 addresses and nicknames from each line  contain-
       ing  a  matching  official  name or nickname. A call to getipnodebyname(3SOCKET) is similar, but is capable of returning hostent structures
       containing IPv4 and IPv6 addresses. Applications might prefer to use the address-family independent getaddrinfo(3SOCKET) API  for  name-to-
       address lookups.

       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 one of two ways:

	   o	  The  conventional  "decimal  dot"  notation  and  interpreted using the inet_addr routine from the Internet address manipulation
		  library, inet(3SOCKET).

	   o	  The IP Version 6 protocol [IPV6], defined in RFC 1884 and interpreted using the inet_pton() routine from  the  Internet  address
		  manipulation library. See inet(3SOCKET).

       This interface supports node 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.

EXAMPLES

       Example 1 Example hosts File Entry

       The following is a typical line from the hosts file:

	 192.9.1.20	   gaia 		       # John Smith

       Example 2 Example IPv6 Address Entry

       The following is an example of an IPv6 hosts entry:

	 2001:0db8:3c4d:55:a00:20ff:fe8e:f3ad  myhost  # John Smith

SEE ALSO

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

       Braden, B., editor, RFC 1123, Requirements for Internet Hosts - Application and Support, Network Working Group, October, 1989.

       Harrenstien, K., Stahl, M., and Feinler, E., RFC 952, DOD Internet Host Table Specification, Network Working Group, October 1985.

       Hinden, R., and Deering, S., editors, RFC 1884, IP Version 6 Addressing Architecture, Network Working Group, December, 1995.

       Postel, Jon, RFC 921, Domain Name System Implementation Schedule (Revised), Network Working Group, October 1984.

NOTES

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

       The symbolic link /etc/net/ipnodes exists for backwards compatibility with previous Solaris releases.

SunOS 5.11							    24 Feb 2008 							  hosts(4)