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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
     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
     constructed 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
                 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(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
                 normally 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
                 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
                 modified.  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.

                 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
                               different 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
                               giving 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
                               automatically reloaded.  The default for n is
                               two seconds.  Setting it to zero disables the
                               file check.

                 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 11.1-RELEASE-p4        October 12, 2015        FreeBSD 11.1-RELEASE-p4
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