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OpenSolaris 2009.06 - man page for hosts (opensolaris section 4)

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hosts(4)				   File Formats 				 hosts(4)

       hosts - host name database




       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 information 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

       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

       For a host with more than one IP address, consecutive entries for these addresses may con-
       tain  the  same	or differing nicknames. Different nicknames are useful for assigning dis-
       tinct 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 containing a matching official name or nickname. A
       call to getipnodebyname(3SOCKET) is similar, but is capable of  returning  hostent  struc-
       tures  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

       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 alpha-
       betical 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 char-
       acter 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 hosts File Entry

       The following is a typical line from the hosts file:	   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

       gethostbyname(3NSL),	getipnodebyname(3SOCKET),     inet(3SOCKET),	nsswitch.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 Specifica-
       tion, Network Working Group, October 1985.

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

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

       /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)
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