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RESOLVER(5)		  FreeBSD File Formats Manual		   RESOLVER(5)

     resolver -- resolver configuration	file


     The resolver(3) is	a set of routines in the C library which provide ac-
     cess 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 re-
		 solver	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	traf-
		 fic 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
		 of the	net.  The IP address and optional network pairs	are
		 separated by slashes.	Up to 10 pairs may be specified.


     options	 Options allows	certain	internal resolver variables to be mod-
		 ified.	 The syntax is

		 options option	...

		 where option is one of	the following:

		 debug	       sets RES_DEBUG in _res.options.

		 usevc	       sets RES_USEVC to use TCP instead of UDP	for

		 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",	mean-
			       ing 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

		 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	de-
			       fault 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.

			       The resolver checks the modification time of
			       /etc/resolv.conf	every n	seconds.  If
			       /etc/resolv.conf	has changed, it	is automati-
			       cally reloaded.	The default for	n is two sec-
			       onds.  Setting it to zero disables the file

		 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 (for
     example, nameserver) must start the line.	The value follows the keyword,
     separated by white	space.

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

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

     Name Server Operations Guide for BIND.

     The resolv.conf file format appeared in 4.3BSD.

FreeBSD	13.0			August 16, 2018			  FreeBSD 13.0


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