resolv.conf - resolver configuration file




     The resolver is a set of routines that provide access to the
     Internet   Domain   Name   System.   See  resolver(3RESOLV).
     resolv.conf is a configuration file that contains the infor-
     mation  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.

     The resolv.conf file contains  the  following  configuration

           Specifies the Internet address in dot-notation  format
           of  a name server that the resolver is to query. Up to
           MAXNS name servers may be listed, one per keyword. See
           <resolv.h>.   If   there  are  multiple  servers,  the
           resolver library queries them in the order listed.  If
           no  name  server  entries  are  present,  the resolver
           library queries the name server on the local  machine.
           The  resolver  library  follows the algorithm to try a
           name server until the query times out.  It then  tries
           the  the  name  servers  that follow, until each query
           times out. It repeats all the  name  servers  until  a
           maximum number of retries are made.

           Specifies the 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  sysinfo(2)  or from
           gethostname(3C). (Everything after the  first  `.'  is
           presumed to be the domain name.) If the host name does
           not contain a domain part, the root domain is assumed.
           You  can  use  the LOCALDOMAIN environment variable to
           override the domain name.

           The 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.  You
           can change the default behavior 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. This
           process may be slow and will generate a lot of network
           traffic  if the servers for the listed domains are not
           local. Queries will time out if no server is available
           for one of the domains.

           The search list is currently limited  to  six  domains
           and a total of 256 characters.

           Allows addresses returned  by  the  libresolv-internal
           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:


           Allows certain internal resolver variables to be modi-
           fied. The syntax is

           options option ...

           where option is one of the following:

           debug Sets RES_DEBUG in the _res.options field.

                 Sets a threshold floor for the  number  of  dots
                 which must appear in a name given to res_query()
                 before an initial absolute (as-is) query is per-
                 formed. See resolver(3RESOLV). The default value
                 for n is 1, which means that if  there  are  any
                 dots  in  a  name, the name is 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 by means of a different  name
                 server.  Measured  in  seconds,  the  default is
                 RES_TIMEOUT. See  <resolv.h>.  The  timeout  and
                 retrans  values  are  the  starting point for an
                 exponential back off procedure where the timeout
                 is doubled for every retransmit attempt.


                 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 application.
                  The default is RES_DFLRETRY. See <resolv.h>.

                 Sets  RES_ROTATE  in  _res.options.   The   name
                 servers are queried round-robin from among those
                 listed. The  query  load  is  spread  among  all
                 listed  servers,  rather than having all clients
                 try the first listed server first every time.

                 Sets RES_NOCHECKNAME in _res.options. This  dis-
                 ables  the modern BIND checking of incoming host
                 names and mail names for invalid characters such
                 as underscore (_), non-ASCII, or control charac-

           inet6 Sets  RES_USE_INET6  in  _res.options.  In   the
                 Solaris   BIND  port,  this  has  no  effect  on
                 gethostbyname(3NSL). To retrieve IPv6  addresses
                 or   IPv4   addresses   in   mapped   form,  use
                 getipnodebyname(3SOCKET)  instead   of   setting

     The domain and search keywords are  mutually  exclusive.  If
     more  than  one  instance  of these keywords is present, the
     last instance takes precedence.

     You  can  override  the  search  keyword   of   the   system
     resolv.conf  file  on  a  per-process  basis  by setting the
     environment variable LOCALDOMAIN to a  space-separated  list
     of search domains.

     You can amend the options keyword of the system  resolv.conf
     file on a per-process basis by setting the environment vari-
     able RES_OPTIONS  to  a  space-separated  list  of  resolver

     The keyword and value must appear on a  single  line.  Start
     the line with the keyword, for example, nameserver, followed
     by the value, separated by white space.




     See attributes(5) for descriptions of the  following  attri-

    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    | Interface Stability         | Standard BIND 8.2.4         |


     domainname(1M),          in.named(1M),           sysinfo(2),
     gethostbyname(3NSL),               getipnodebyname(3SOCKET),
     gethostname(3C), resolver(3RESOLV), attributes(5)

     Vixie, Paul, Dunlap,  Keven  J.,  Karels,  Michael  J.  Name
     Server  Operations Guide for BIND. Internet Software Consor-
     tium, 1996.

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