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RedHat 9 (Linux i386) - man page for resolver (redhat section 5)

RESOLVER(5)			     BSD File Formats Manual			      RESOLVER(5)

     resolver -- resolver configuration file


     The resolver is a set of routines in the C library (resolve(3)) 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 vari-
     ous 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 directives are:

	      Internet address (in dot notation) of a name server that the resolver should query.
	      Up to MAXNS (see <resolv.h>) 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 deter-
	      mined 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 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.

	      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.  For example:


     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.

			sets the amount of time the resolver will wait for a response from a
			remote name server before retrying the query via a different name server.
			Measured in seconds, the default is RES_TIMEOUT (see <resolv.h> ).

			sets the number of times the resolver will send a query to its name
			servers before giving up and returning an error to the calling applica-
			tion.  The default is RES_DFLRETRY (see <resolv.h> ).

	      rotate	sets RES_ROTATE in _res.options, which causes round robin selection of
			nameservers from among those listed.  This has the effect of spreading
			the query load among all listed servers, rather than having all clients
			try the first listed server first every time.

			sets RES_NOCHECKNAME in _res.options, which disables the modern BIND
			checking of incoming host names and mail names for invalid characters
			such as underscore (_), non-ASCII, or control characters.

	      inet6	sets RES_USE_INET6 in _res.options.  This has the effect of trying a AAAA
			query before an A query inside the gethostbyname function, and of mapping
			IPv4 responses in IPv6 ``tunnelled form'' if no AAAA records are found
			but an A record set exists.

     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

     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.

     /etc/resolv.conf <resolv.h>

     gethostbyname(3), hostname(7), named(8), resolver(3), resolver(5).  ``Name Server Operations
     Guide for BIND''

4th Berkeley Distribution		November 11, 1993		4th Berkeley Distribution

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