.\" $OpenBSD: resolv.conf.5,v 1.2 1996/03/29 10:17:50 niklas Exp $ .\" $NetBSD: resolv.conf.5,v 1.7 1996/03/06 18:22:16 scottr Exp $ .\" .\" Copyright (c) 1986, 1991 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 5.12 (Berkeley) 5/10/91 .\" .Dd May 10, 1991 .Dt RESOLV.CONF 5 .Os BSD 4 .Sh NAME .Nm resolv.conf .Nd resolver configuration file .Sh DESCRIPTION The .Nm resolv.conf file specifies how the .Xr resolver 3 routines in the C library (which provide access to the Internet Domain Name System) should operate. 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 lookup This keyword is used by the library routines .Xr gethostbyname 3 and .Xr gethostbyaddr 3 . It specifies which databases should be searched, and the order to do so. The legal space-separated values are .Bl -tag -width bind .It Sy bind use the Domain Name server by querying the .Xr named 8 .It Sy file search for entries in .Nm /etc/hosts .It Sy yp talk to the YP system if .Xr ypbind 8 is running .El .Pp If the .Sy lookup keyword is not used in the system's .Pa resolv.conf file then the assumed order is .Sy bind file . Furthermore, if the system's .Pa resolv.conf file does not exist, then the only database used is .Sy file . .Pp .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 1024 characters. .It Sy sortlist Sortlist allows addresses returned by gethostbyname to be sorted. A 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 seperated by slashes. Up to 10 pairs may be specified, ie. .Pp .Sy sortlist 130.155.160.0/255.255.240.0 130.155.0.0 .It Sy options Options allows certain internal resolver variables to be modified. The syntax is: .Pp .Sy options option ... .Pp where option is one of the following: .Bl -tag -width ndots:n .It Sy debug sets RES_DEBUG in _res.options. .It Sy ndots:n sets a threshold for the number of dots which must appear in a name given to res_query (see .Xr resolver 3 ) before an initial absolute query will be made. The default for n is 1, meaning that if there are any dots in a name, the name will be tried first as an absolute name before any search list elements are appended to it. .El .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 .Sy search keyword of a system's .Pa resolv.conf file can be overridden on a per-process basis by setting the environment variable .Ev LOCALDOMAIN to a space-separated list of search domains. .Pp The .Sy options keyword of a system's .Pa resolv.conf file can be amended on a per-process basis by setting the environment variable .Ev RES_OPTIONS to a space-separated list of resolver options as explained above. .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 .