resolver(5)

NAME

       resolver - resolver configuration file

SYNOPSIS

       /etc/resolv.conf

DESCRIPTION

       The  resolver  is  a set of routines in the C library 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 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  (cur­
              rently  3) name servers may be listed, one per key­
              word.  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(); 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.

              e.g.      sortlist      130.155.160.0/255.255.240.0
              130.155.0.0

       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(@LIB_NETWORK_EXT@))  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  environ­
       ment 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 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.

FILES

       /etc/resolv.conf

SEE ALSO

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