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HOSTS(4)							      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 informa‐
       tion in the hosts file.

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

       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  alterna‐
       tive  names  for	 the  same  machine,  or  "nicknames."	Nicknames  are

       For a host with more than one IP address, consecutive entries for these
       addresses  may contain the same or differing nicknames. Different nick‐
       names 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 containing
       a  matching  official  name  or	nickname.  A  call   to	  getipnodeby‐
       name(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 manip‐
		  ulation 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 maxi‐
       mum 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),  nss‐
       witch.conf(4), resolv.conf(4)

       Braden, B., editor, RFC 1123, Requirements for Internet Hosts -	Appli‐
       cation 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.

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

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

				 Feb 24, 2008			      HOSTS(4)

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