resolver.5

早期freebsd实现

.\" Copyright (c) 1986, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\"    must display the following acknowledgement:
.\"	This product includes software developed by the University of
.\"	California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\"     @(#)resolver.5	8.1 (Berkeley) 6/5/93
.\"
.Dd June 5, 1993
.Dt RESOLVER 5
.Os BSD 4
.Sh NAME
.Nm resolver
.Nd resolver configuration file
.Sh SYNOPSIS
.Nm resolv.conf
.Sh DESCRIPTION
The
.Xr resolver 3
is a set of routines in the C library
which 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.
.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 nameserver
.It Sy nameserver
Internet address (in dot notation) of a name server
that the resolver should query.
Up to
.Dv 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
.Sy 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 Sy domain
Local domain name.
Most queries for names within this domain can use short names
relative to the local domain.
If no
.Sy domain
entry is present, the domain is determined
from the local host name returned by
.Xr 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.
.It Sy search
Search list for host-name lookup.
The search list is normally determined from the local domain name;
by default, it begins with the local domain name, then successive
parent domains that have at least two components in their names.
This may be changed by listing the desired domain search path
following the
.Sy 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.
.Pp
The search list is currently limited to six domains
with a total of 256 characters.
.El
.Pp
The
.Sy domain
and
.Sy search
keywords are mutually exclusive.
If more than one instance of these keywords is present,
the last instance will override.
.Pp
The keyword and value must appear on a single line, and the keyword
(e.g.
.Sy nameserver )
must start the line.  The value follows
the keyword, separated by white space.
.Sh FILES
.Bl -tag -width /etc/resolv.conf -compact
.It Pa /etc/resolv.conf
The file
.Nm resolv.conf
resides in
.Pa /etc .
.El
.Sh SEE ALSO
.Xr gethostbyname 3 ,
.Xr resolver 3 ,
.Xr hostname 7 ,
.Xr named 8
.Rs
.%T "Name Server Operations Guide for BIND"
.Re
.Sh HISTORY
The
.Nm resolv.conf
file format appeared in
.Bx 4.3 .