1.\" Copyright (c) 1986, 1991 The Regents of the University of California. 2.\" 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 5.12 (Berkeley) 5/10/91 33.\" 34.Dd May 10, 1991 35.Dt RESOLVER 5 36.Os BSD 4 37.Sh NAME 38.Nm resolver 39.Nd resolver configuration file 40.Sh SYNOPSIS 41.Nm resolv.conf 42.Sh DESCRIPTION 43The 44.Xr resolver 3 45is a set of routines in the C library 46which provide access to the Internet Domain Name System. 47The resolver configuration file contains information that is read 48by the resolver routines the first time they are invoked by a process. 49The file is designed to be human readable and contains a list of 50keywords with values that provide various types of resolver information. 51.Pp 52On a normally configured system this file should not be necessary. 53The only name server to be queried will be on the local machine, 54the domain name is determined from the host name, 55and the domain search path is constructed from the domain name. 56.Pp 57The different configuration options are: 58.Bl -tag -width nameserver 59.It Sy nameserver 60Internet address (in dot notation) of a name server 61that the resolver should query. 62Up to 63.Dv MAXNS 64(currently 3) name servers may be listed, 65one per keyword. 66If there are multiple servers, 67the resolver library queries them in the order listed. 68If no 69.Sy nameserver 70entries are present, 71the default is to use the name server on the local machine. 72(The algorithm used is to try a name server, and if the query times out, 73try the next, until out of name servers, 74then repeat trying all the name servers 75until a maximum number of retries are made). 76.It Sy domain 77Local domain name. 78Most queries for names within this domain can use short names 79relative to the local domain. 80If no 81.Sy domain 82entry is present, the domain is determined 83from the local host name returned by 84.Xr gethostname 2 ; 85the domain part is taken to be everything after the first `.'. 86Finally, if the host name does not contain a domain part, the root 87domain is assumed. 88.It Sy search 89Search list for host-name lookup. 90The search list is normally determined from the local domain name; 91by default, it begins with the local domain name, then successive 92parent domains that have at least two components in their names. 93This may be changed by listing the desired domain search path 94following the 95.Sy search 96keyword with spaces or tabs separating 97the names. 98Most resolver queries will be attempted using each component 99of the search path in turn until a match is found. 100Note that this process may be slow and will generate a lot of network 101traffic if the servers for the listed domains are not local, 102and that queries will time out if no server is available 103for one of the domains. 104.Pp 105The search list is currently limited to six domains 106with a total of 256 characters. 107.El 108.Pp 109The 110.Sy domain 111and 112.Sy search 113keywords are mutually exclusive. 114If more than one instance of these keywords is present, 115the last instance will override. 116.Pp 117The keyword and value must appear on a single line, and the keyword 118(e.g. 119.Sy nameserver ) 120must start the line. The value follows 121the keyword, separated by white space. 122.Sh FILES 123.Bl -tag -width /etc/resolv.conf -compact 124.It Pa /etc/resolv.conf 125The file 126.Nm resolv.conf 127resides in 128.Pa /etc . 129.El 130.Sh SEE ALSO 131.Xr gethostbyname 3 , 132.Xr resolver 3 , 133.Xr hostname 7 , 134.Xr named 8 135.Rs 136.%T "Name Server Operations Guide for BIND" 137.Re 138.Sh HISTORY 139The 140.Nm resolv.conf 141file format appeared in 142.Bx 4.3 . 143