1.\" Copyright (c) 1986, 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" @(#)resolver.5 8.1 (Berkeley) 6/5/93 33.\" $Id$ 34.\" 35.Dd June 5, 1993 36.Dt RESOLVER 5 37.Os BSD 4 38.Sh NAME 39.Nm resolver 40.Nd resolver configuration file 41.Sh SYNOPSIS 42.Nm resolv.conf 43.Sh DESCRIPTION 44The 45.Xr resolver 3 46is a set of routines in the C library 47which provide access to the Internet Domain Name System. 48The resolver configuration file contains information that is read 49by the resolver routines the first time they are invoked by a process. 50The file is designed to be human readable and contains a list of 51keywords with values that provide various types of resolver information. 52.Pp 53On a normally configured system this file should not be necessary. 54The only name server to be queried will be on the local machine, 55the domain name is determined from the host name, 56and the domain search path is constructed from the domain name. 57.Pp 58The different configuration options are: 59.Bl -tag -width nameserver 60.It Sy nameserver 61Internet address (in dot notation) of a name server 62that the resolver should query. 63Up to 64.Dv MAXNS 65(currently 3) name servers may be listed, 66one per keyword. 67If there are multiple servers, 68the resolver library queries them in the order listed. 69If no 70.Sy nameserver 71entries are present, 72the default is to use the name server on the local machine. 73(The algorithm used is to try a name server, and if the query times out, 74try the next, until out of name servers, 75then repeat trying all the name servers 76until a maximum number of retries are made). 77.It Sy domain 78Local domain name. 79Most queries for names within this domain can use short names 80relative to the local domain. 81If no 82.Sy domain 83entry is present, the domain is determined 84from the local host name returned by 85.Xr gethostname 3 ; 86the domain part is taken to be everything after the first `.'. 87Finally, if the host name does not contain a domain part, the root 88domain is assumed. 89.It Sy search 90Search list for host-name lookup. 91The search list is normally determined from the local domain name; 92by default, it begins with the local domain name, then successive 93parent domains that have at least two components in their names. 94This may be changed by listing the desired domain search path 95following the 96.Sy search 97keyword with spaces or tabs separating 98the names. 99Most resolver queries will be attempted using each component 100of the search path in turn until a match is found. 101Note that this process may be slow and will generate a lot of network 102traffic if the servers for the listed domains are not local, 103and that queries will time out if no server is available 104for one of the domains. 105.Pp 106The search list is currently limited to six domains 107with a total of 256 characters. 108.El 109.Pp 110The 111.Sy domain 112and 113.Sy search 114keywords are mutually exclusive. 115If more than one instance of these keywords is present, 116the last instance will override. 117.Pp 118The keyword and value must appear on a single line, and the keyword 119(e.g. 120.Sy nameserver ) 121must start the line. The value follows 122the keyword, separated by white space. 123.Sh FILES 124.Bl -tag -width /etc/resolv.conf -compact 125.It Pa /etc/resolv.conf 126The file 127.Nm resolv.conf 128resides in 129.Pa /etc . 130.El 131.Sh SEE ALSO 132.Xr gethostbyname 3 , 133.Xr resolver 3 , 134.Xr hostname 7 , 135.Xr named 8 136.Rs 137.%T "Name Server Operations Guide for BIND" 138.Re 139.Sh HISTORY 140The 141.Nm resolv.conf 142file format appeared in 143.Bx 4.3 . 144