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     resolver -- resolver configuration file




     The resolver(3) is a set of routines in the C library which 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.

     On a normally configured system this file should not be necessary.  The
     only name server to be queried will be on the local machine, the domain
     name is determined from the host name, and the domain search path is con-
     structed from the domain name.

     The different configuration options are:

     nameserver  Internet address (in dot notation) of a name server that the
		 resolver should query.  Up to MAXNS (currently 3) name
		 servers may be listed, one per keyword.  If there are multi-
		 ple 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 to try a name server, and if the query times out, try
		 the next, until out of name servers, then repeat trying all
		 the name servers until a maximum number of retries are 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(3); the domain part
		 is taken to be everything after the first `.'.  Finally, if
		 the host name does not contain a domain part, the root domain
		 is assumed.

     search	 Search list for host-name lookup.  The search list is nor-
		 mally determined from the local domain name; by default, it
		 contains only the local domain name.  This may 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 component of
		 the search path in turn until a match is found.  Note that
		 this process may be slow and will generate a lot of network
		 traffic if the servers for the listed domains are not local,
		 and that queries will 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.

     sortlist	 Sortlist allows addresses returned by gethostbyname to be
		 sorted.  A sortlist is specified by IP address netmask pairs.
		 The netmask is optional and defaults to the natural netmask

		 options option ...

		 where option is one of the following:

		 debug	       sets RES_DEBUG in _res.options.

		 ndots:n       sets a threshold for the number of dots which
			       must appear in a name given to res_query() (see
			       resolver(3)) 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.

		 timeout:n     sets the initial amount of time the resolver
			       will wait for a response from a remote name
			       server before retrying the query via a differ-
			       ent name server.  The resolver may wait longer
			       during subsequent retries of the current query
			       since an exponential back-off is applied to the
			       timeout value.  Measured in seconds, the
			       default is RES_TIMEOUT, the allowed maximum is
			       RES_MAXRETRANS (see <resolv.h>).

		 attempts:n    sets the number of times the resolver will send
			       a query to each of its name servers before giv-
			       ing up and returning an error to the calling
			       application.  The default is RES_DFLRETRY, the
			       allowed maximum is RES_MAXRETRY (see

		 no_tld_query  tells the resolver not to attempt to resolve a
			       top level domain name, that is, a name that
			       contains no dots.  Use of this option does not
			       prevent the resolver from obeying the standard
			       domain and search rules with the given name.

		 Options may also be specified as a space or tab separated
		 list using the RES_OPTIONS environment variable.

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

     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, sepa-
     rated by white space.


     /etc/resolv.conf  The file resolv.conf resides in /etc.


     gethostbyname(3), resolver(3), hostname(7), named(8)

     Name Server Operations Guide for BIND.



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