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.\" $FreeBSD: src/share/man/man5/resolver.5,v 1.7.2.1 2001/08/17 13:08:47 ru Exp $ 34.\" $DragonFly: src/share/man/man5/resolver.5,v 1.4 2008/05/02 02:05:06 swildner Exp $ 35.\" 36.Dd November 11, 1993 37.Dt RESOLVER 5 38.Os 39.Sh NAME 40.Nm resolver 41.Nd resolver configuration file 42.Sh SYNOPSIS 43.Nm resolv.conf 44.Sh DESCRIPTION 45The 46.Xr resolver 3 47is a set of routines in the C library 48which provide access to the Internet Domain Name System. 49The resolver configuration file contains information that is read 50by the resolver routines the first time they are invoked by a process. 51The file is designed to be human readable and contains a list of 52keywords with values that provide various types of resolver information. 53.Pp 54On a normally configured system this file should not be necessary. 55The only name server to be queried will be on the local machine, 56the domain name is determined from the host name, 57and the domain search path is constructed from the domain name. 58.Pp 59The different configuration options are: 60.Bl -tag -width nameserver 61.It Sy nameserver 62Internet address (in dot notation) of a name server 63that the resolver should query. 64Up to 65.Dv MAXNS 66(currently 3) name servers may be listed, 67one per keyword. 68If there are multiple servers, 69the resolver library queries them in the order listed. 70If no 71.Sy nameserver 72entries are present, 73the default is to use the name server on the local machine. 74(The algorithm used is to try a name server, and if the query times out, 75try the next, until out of name servers, 76then repeat trying all the name servers 77until a maximum number of retries are made). 78.It Sy domain 79Local domain name. 80Most queries for names within this domain can use short names 81relative to the local domain. 82If no 83.Sy domain 84entry is present, the domain is determined 85from the local host name returned by 86.Xr gethostname 3 ; 87the domain part is taken to be everything after the first `.'. 88Finally, if the host name does not contain a domain part, the root 89domain is assumed. 90.It Sy search 91Search list for host-name lookup. 92The search list is normally determined from the local domain name; 93by default, it contains only the local domain name. 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.It Sy sortlist 109Sortlist allows addresses returned by gethostbyname to be sorted. 110A sortlist is specified by IP address netmask pairs. 111The netmask is 112optional and defaults to the natural netmask of the net. 113The IP address 114and optional network pairs are separated by slashes. 115Up to 10 pairs may 116be specified. 117.Pp 118e.g. sortlist 130.155.160.0/255.255.240.0 130.155.0.0 119.It Sy options 120Options allows certain internal resolver variables to be modified. 121The syntax is 122.Pp 123\fBoptions\fP \fIoption\fP \fI...\fP 124.Pp 125where 126.Sy option 127is one of the following: 128.Bl -tag -width no_tld_query 129.It Sy debug 130sets 131.Dv RES_DEBUG 132in _res.options. 133.It Sy ndots:n 134sets a threshold for the number of dots which must appear in a name given to 135.Fn res_query 136(see 137.Xr resolver 3 ) 138before an 139.Em initial absolute query 140will be made. 141The default for 142.Em n 143is 144.Dq 1 , 145meaning that if there are any dots in a name, the name 146will be tried first as an absolute name before any 147.Em search list 148elements are appended to it. 149.It Sy no_tld_query 150tells the resolver not to attempt to resolve a top level domain name, that 151is, a name that contains no dots. Use of this option doesn't prevent 152the resolver from obeying the standard 153.Sy domain 154and 155.Sy search 156rules with the given name. 157.El 158.Pp 159Options may also be specified as a space or tab separated list using the 160.Ev RES_OPTIONS 161environment variable. 162.El 163.Pp 164The 165.Sy domain 166and 167.Sy search 168keywords are mutually exclusive. 169If more than one instance of these keywords is present, 170the last instance will override. 171.Pp 172The keyword and value must appear on a single line, and the keyword 173(e.g.\& 174.Sy nameserver ) 175must start the line. The value follows 176the keyword, separated by white space. 177.Sh FILES 178.Bl -tag -width /etc/resolv.conf -compact 179.It Pa /etc/resolv.conf 180The file 181.Nm resolv.conf 182resides in 183.Pa /etc . 184.El 185.Sh SEE ALSO 186.Xr gethostbyname 3 , 187.Xr resolver 3 , 188.Xr hostname 7 , 189.Xr named 8 190.Rs 191.%T "Name Server Operations Guide for BIND" 192.Re 193.Sh HISTORY 194The 195.Nm resolv.conf 196file format appeared in 197.Bx 4.3 . 198