184 lines
5.6 KiB
Groff
184 lines
5.6 KiB
Groff
.\" Copyright (c) 1986 The Regents of the University of California.
|
|
.\" All rights reserved.
|
|
.\"
|
|
.\" Redistribution and use in source and binary forms are permitted
|
|
.\" provided that the above copyright notice and this paragraph are
|
|
.\" duplicated in all such forms and that any documentation,
|
|
.\" advertising materials, and other materials related to such
|
|
.\" distribution and use acknowledge that the software was developed
|
|
.\" by the University of California, Berkeley. The name of the
|
|
.\" University may not be used to endorse or promote products derived
|
|
.\" from this software without specific prior written permission.
|
|
.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
|
|
.\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
|
|
.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
|
|
.\"
|
|
.\" @(#)resolver.5 5.9 (Berkeley) 12/14/89
|
|
.\" $Id: resolver.5,v 8.4 1997/03/14 02:29:49 vixie Exp $
|
|
.\"
|
|
.Dd November 11, 1993
|
|
.Dt RESOLVER @FORMAT_EXT_U@
|
|
.Os BSD 4
|
|
.Sh NAME
|
|
.Nm resolver
|
|
.Nd resolver configuration file
|
|
.Sh SYNOPSIS
|
|
.Pa /etc/resolv.conf
|
|
.Sh DESCRIPTION
|
|
The
|
|
.Nm resolver
|
|
is a set of routines in the C library
|
|
.Pq Xr resolve @LIB_NETWORK_EXT@
|
|
that provide access to the Internet Domain Name System.
|
|
The
|
|
.Nm resolver
|
|
configuration file contains information that is read
|
|
by the
|
|
.Nm 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
|
|
.Nm resolver
|
|
information.
|
|
.Pp
|
|
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.
|
|
.Pp
|
|
The different configuration options are:
|
|
.Bl -tag -width "nameser"
|
|
.It Li nameserver
|
|
Internet address (in dot notation) of a name server that the
|
|
.Nm resolver
|
|
should query. Up to
|
|
.Dv MAXNS
|
|
(currently 3) name servers may be listed, one per keyword.
|
|
If there are multiple servers, the
|
|
.Nm resolver
|
|
library queries them in the order listed.
|
|
If no
|
|
.Li 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).
|
|
.It Li domain
|
|
Local domain name.
|
|
Most queries for names within this domain can use short names
|
|
relative to the local domain.
|
|
If no
|
|
.Li domain
|
|
entry is present, the domain is determined from the local host name returned by
|
|
.Xr gethostname @BSD_SYSCALL_EXT@ ;
|
|
the domain part is taken to be everything after the first
|
|
.Sq \&. .
|
|
Finally, if the host name does not contain a domain part, the root
|
|
domain is assumed.
|
|
.It Li 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
|
|
.Li search
|
|
keyword with spaces or tabs separating the names.
|
|
Most
|
|
.Nm 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.
|
|
.Pp
|
|
The search list is currently limited to six domains
|
|
with a total of 256 characters.
|
|
.It Li sortlist
|
|
Allows addresses returned by gethostbyname to be sorted.
|
|
A
|
|
.Li 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:
|
|
.Bd -literal -offset indent
|
|
sortlist 130.155.160.0/255.255.240.0 130.155.0.0
|
|
.Ed
|
|
.It Li options
|
|
Allows certain internal
|
|
.Nm resolver
|
|
variables to be modified.
|
|
The syntax is
|
|
.D1 Li options Ar option ...
|
|
where
|
|
.Ar option
|
|
is one of the following:
|
|
.Bl -tag -width "ndots:n "
|
|
.It Li debug
|
|
sets
|
|
.Dv RES_DEBUG
|
|
in
|
|
.Ft _res.options .
|
|
.It Li ndots: Ns Ar n
|
|
sets a threshold for the number of dots which
|
|
must appear in a name given to
|
|
.Fn res_query
|
|
(see
|
|
.Xr resolver @LIB_NETWORK_EXT@ )
|
|
before an
|
|
.Em initial absolute query
|
|
will be made. The default for
|
|
.Ar n
|
|
is
|
|
.Dq 1 ,
|
|
meaning that if there are
|
|
.Em any
|
|
dots in a name, the name will be tried first as an absolute name before any
|
|
.Em search list
|
|
elements are appended to it.
|
|
.El
|
|
.El
|
|
.Pp
|
|
The
|
|
.Li domain
|
|
and
|
|
.Li search
|
|
keywords are mutually exclusive.
|
|
If more than one instance of these keywords is present,
|
|
the last instance wins.
|
|
.Pp
|
|
The
|
|
.Li search
|
|
keyword of a system's
|
|
.Pa resolv.conf
|
|
file can be
|
|
overridden on a per-process basis by setting the environment variable
|
|
.Dq Ev LOCALDOMAIN
|
|
to a space-separated list of search domains.
|
|
.Pp
|
|
The
|
|
.Li options
|
|
keyword of a system's
|
|
.Pa resolv.conf
|
|
file can be amended on a per-process basis by setting the environment variable
|
|
.Dq Ev RES_OPTIONS to a space-separated list of
|
|
.Nm resolver
|
|
options as explained above under
|
|
.Li options .
|
|
.Pp
|
|
The keyword and value must appear on a single line, and the keyword
|
|
(e.g.,
|
|
.Li nameserver )
|
|
must start the line. The value follows the keyword, separated by white space.
|
|
.Sh FILES
|
|
.Pa /etc/resolv.conf
|
|
.Sh SEE ALSO
|
|
.Xr gethostbyname @LIB_NETWORK_EXT@ ,
|
|
.Xr hostname @DESC_EXT@ ,
|
|
.Xr @INDOT@named @SYS_OPS_EXT@ ,
|
|
.Xr resolver @LIB_NETWORK_EXT@ ,
|
|
.Xr resolver @FORMAT_EXT@ .
|
|
.Dq Name Server Operations Guide for Sy BIND
|