Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages


home | help
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. 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  alterna-
       tive  names  for	 the  same  machine, or	"nicknames." Nicknames are op-

       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 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" nota-
       tion and	interpreted using the inet_addr	routine	from the Internet  ad-
       dress manipulation library, inet(3SOCKET).

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

	      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  al-
	      lowed  when  they	 serve	to delimit components of "domain style
	      names".  (See RFC	921, "Domain Name System Implementation	Sched-
	      ule,"  for background). No blank or space	characters are permit-
	      ted 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 of a typical line from the hosts file.

       Here is a typical line from the hosts file:	 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  sym-
       bolic link /etc/hosts exists for	BSD compatibility.

				  30 Sep 2005			      hosts(4)


Want to link to this manual page? Use this URL:

home | help