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NAME    [Toc]    [Back]

       resolver - resolver configuration file

SYNOPSIS    [Toc]    [Back]


DESCRIPTION    [Toc]    [Back]

       The  resolver  is  a set of routines in the C library that
       provide access to the Internet  Domain  Name  System.  The
       resolver  configuration file (resolv.conf) contains information
 that is read by the  resolver  routines  the  first
       time  they  are invoked by a process. The file is designed
       to be read by humans and contains a list of keywords  with
       values that provide various types of resolver information.

       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).  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 dot (.).  Finally, if the host name does
       not contain a domain part, the  root  domain  is  assumed.
       Search  list  for host name lookup. By default, the search
       list consists of the local domain name.   You  can  change
       this  system wide by specifying search keyword followed by
       a list of domain names separated by spaces or tabs, or  on
       a per-process basis by specifying the LOCALDOMAIN environment
 variable followed by a list of domain names separated
       by spaces or tabs.

              Most  resolver queries will be attempted using each
              component of the search path in turn until a  match
              is  found.  This process might be slow and 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.  Enables the  sorting
   of  addresses  returned  by  gethostname.   A
              sortlist  comprises  pairs  of  IP  addresses   and
              optional  netmasks;  each  IP  address and optional
              netmask are separated by  a  slash  character  (/).
              The  netmask  is optional, and defaults to the current
 network netmask.  You can  specify  up  to  10
              pairs.  For example:

              Option for host name lookup.  By  default,  when  a
              host  name  contains one or more dots (.), resolver
              looks up the name  as  given  before  applying  the
              search list.  The n specifies the minimum number of
              dots a name must contain in order to be  looked  up
              as  given  before  applying  the  search list.  The
              range is from 0 to 15.

              You can change the resolver options system wide  by
              specifying  options  keyword  followed  a  list  of
              resolver options separated by spaces, or on a  perprocess
  basis  by specifying the RES_OPTIONS environment
 variable followed by  a  list  of  resolver
              options separated by spaces.

       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.

FILES    [Toc]    [Back]


SEE ALSO    [Toc]    [Back]

       Functions:   dn_comp(3),  dn_expand(3),  gethostbyname(3),
       res_init(3), res_mkquery(3), res_query(3),  res_search(3),

       Files: hostname(5)

       Commands: named(8)

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