resolver man page on 4.4BSD

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RESOLVER(5)			      11,			   RESOLVER(5)

       resolver - resolver configuration file


       The  resolver  is  a  set of routines in the C library (resolv(3)) that
       provide access to the Internet Domain Name System.  The	resolver  con‐
       figuration  file contains information that is read by the resolver rou‐
       tines the first time they are  invoked  by  a  process.	 The  file  is
       designed to be human readable and contains a list of keywords with val‐
       ues 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
       constructed from the domain name.

       The different configuration options are:

	      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 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  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(2); 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  normally
	      determined  from	the  local  domain name; by default, it begins
	      with the local domain name, then successive parent domains  that
	      have  at	least  two  components	in  their  names.  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

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

	      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  of
	      the net. The IP address and optional network pairs are seperated
	      by slashes. Up to 10 pairs may be specified.

	      e.g. sortlist

	      Options allows certain internal resolver variables to  be	 modi‐
	      fied.  The syntax is

	      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.

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

       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

       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.


       gethostbyname(3N), resolver(3), hostname(7), named(8)
       Name Server Operations Guide for BIND

4th Berkeley Distribution					   RESOLVER(5)

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