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 resolver(4)							 resolver(4)

      resolver - resolver configuration file


      The resolver is a set of routines in the C library (see resolver(3N))
      that provide access to the Internet Domain Name System.  The resolver
      configuration file contains information that is read by the resolver
      routines the first time they are invoked by a process.  The file is
      designed to be human-readable, and contains a list of keywords with
      values that provide various types of resolver information.

      If the only name server to be queried is on the local machine, then
      this file is not always necessary. The domain name could be determined
      from the host name (see hostname(1)), if it has been set as a fully
      qualified domain name.

      Recognized configuration options include:

	   nameserver	  Internet (IP) address, in dot notation, of a name
			  server that the resolver should query.  Up to
			  MAXNS (currently 3) name servers can be listed,
			  one per keyword.  If there are multiple servers,
			  the resolver library queries them in the order
			  listed.  If no nameserver entries are present, the
			  default is to use the name server on the local
			  machine.  (The algorithm used is:  Try a name
			  server; if the query times out, try the next and
			  continue until all name servers have been tried,
			  then repeat trying all the name servers until a
			  maximum number of retries have been made).

	   domain	  Local domain name.  Most queries for names within
			  this domain can use short names relative to the
			  local domain.	 If no domain entry is present, the
			  domain is determined from the local host name
			  returned by gethostname() (see gethostname(2));
			  the domain part is interpreted as everything after
			  the first dot (.).  Finally, if the host name does
			  not contain a domain part, the root domain is

	   search	  Search list for host-name lookup.  If the search
			  option is not used the search list will contain
			  only the the local domain name.  The search list
			  can be changed by listing the desired domain
			  search path following the search keyword with
			  spaces or tabs separating the names.	Most
			  resolver queries will be attempted using each

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 resolver(4)							 resolver(4)

			  component of the search path in turn until a match
			  is found.  Note that this process may be slow and
			  generates a lot of network traffic if the servers
			  for the listed domains are not local, and that
			  queries time out if no server is available for one
			  of the domains.

			  The search list is currently limited to six
			  domains with a total of 256 characters.

			  The first domain in the search list must be the
			  local domain for short names to work properly in
			  various files (such as .rhosts and inetd.sec)

	   sortlist	  Causes addresses returned by gethostbyname(3C) to
			  be sorted in accordance with network numbers
			  specified in the address list.  This option allows
			  you to specify which subnets and networks for
			  gethostbyname() to prefer if it receives multiple
			  addresses as the result of a query from the domain
			  nameserver.  The syntax is

			       sortlist addresslist

			  A sortlist is specified by IP address netmask
			  pairs.  The netmask is optional and defaults to
			  the netmask of the net.  The IP address and
			  optional netmask pairs are separated by slashes.
			  Up to 10 pairs may be specified.  The pairs are
			  separated by blank spaces.

			  The following sortlist directive sorts the address
			  on 128.32.42 subnet,


			  The argument after the slash is the subnet mask
			  for the subnet in question.  To prefer an entire
			  network, you can omit the slash and the subnet


			  gethostbyname() sorts any addresses in a reply
			  that match these arguments into the order in which
			  they appear in the sortlist, and appends those
			  addresses that do not match to the end.

	   options	  Options allows certain internal resolver variables
			  to be modified.  The syntax is

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 resolver(4)							 resolver(4)

			       options option  ...

			  where currently the option supported is the

			       ndots:n	      Set a threshold for the number
					      of dots which must appear in a
					      name given to res_query (see
					      resolver(3N)) before an
					      initial absolute query will be
					      made. The default for n is
					      ``1'', meaning that if there
					      are any dots in a name, the
					      name will be tried first as an
					      absolute name before any
					      search list elements are
					      appended to it.

      The domain and search keywords are mutually exclusive.  If more than
      one instance of these keywords is present, the last instance

      The search keyword of a system's resolv.conf file can be overridden on
      a per-process basis by setting the environment variable LOCALDOMAIN to
      a space-separated list of search domains. The options keyword of a
      system's resolv.conf file can be amended on a per-process basis by
      setting the environment variable RES_OPTIONS to a space separated list
      of resolver options as explained above under options.

      The keyword and value must appear on a single line, and the keyword
      (e.g.  nameserver) must start the line.  The value follows the
      keyword, separated by white space.

      Note that the resolver routine res_init() silently ignores errors when
      reading this file (see resolver(3N)).

      A typical resolv.conf file resembles the following:

	   domain div.inc.com

      In order to reduce situations that may cause connections to unintended
      destinations, the administrator should carefully select which domains
      are put in the search list in the resolv.conf file. HP recommends that
      the possible domains for the search list be limited to those domains
      administered within your trusted organization. For more information on
      the security implications of search lists please see RFC 1535, located
      in /usr/share/doc.

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 resolver(4)							 resolver(4)

      resolver was developed by the University of California, Berkeley.

      /etc/resolv.conf		    Resolver configuration file.

      named(1M), resolver(3N), gethostent(3N), hostname(5), RFC 1535

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