.\" Copyright (c) 1986 The Regents of the University of California.
.\" All rights reserved.
.\"
+.\" %%%LICENSE_START(PERMISSIVE_MISC)
.\" Redistribution and use in source and binary forms are permitted
.\" provided that the above copyright notice and this paragraph are
.\" duplicated in all such forms and that any documentation,
.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
.\" WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
+.\" %%%LICENSE_END
.\"
.\" @(#)resolver.5 5.9 (Berkeley) 12/14/89
.\" $Id: resolver.5,v 8.6 1999/05/21 00:01:02 vixie Exp $
.\"
.\" Added ndots remark by Bernhard R. Link - debian bug #182886
.\"
-.TH RESOLV.CONF 5 2012-02-08 "" "Linux Programmer's Manual"
+.TH RESOLV.CONF 5 2014-12-31 "" "Linux Programmer's Manual"
.UC 4
.SH NAME
resolv.conf \- resolver configuration file
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.
+The configuration file is considered a trusted source of DNS information
+(e.g., DNSSEC AD-bit information will be returned unmodified from this
+source).
.LP
-On a normally configured system this file should not be necessary.
-The only name server to be queried will be on the local machine;
+If this file does not exist,
+only the name server on the local machine will be queried;
the domain name is determined from the hostname
and the domain search path is constructed from the domain name.
.LP
The different configuration options are:
.TP
\fBnameserver\fP Name server IP address
-Internet address (in dot notation) of a name server
-that the resolver should query.
+Internet address of a name server that the resolver should query,
+either an IPv4 address (in dot notation),
+or an IPv6 address in colon (and possibly dot) notation as per RFC 2373.
Up to
.B MAXNS
(currently 3, see \fI<resolv.h>\fP) name servers may be listed,
\fBdomain\fP Local domain name.
Most queries for names within this domain can use short names
relative to the local domain.
+If set to \(aq.\(aq, the root domain is considered.
If no \fBdomain\fP entry is present, the domain is determined
from the local hostname returned by
.BR gethostname (2);
sets
.BR RES_DEBUG
in
-.IR _res.options .
+.IR _res.options
+(effective only if glibc was built with debug support; see
+.BR resolver (3)).
.TP
.BI ndots: n
.\" Since glibc 2.2
.BR RES_ROTATE
in
.IR _res.options ,
-which causes round robin selection of nameservers from among those listed.
+which causes round-robin selection of name servers from among those listed.
This has the effect of spreading the query load among all listed servers,
rather than having all clients try the first listed server first every time.
.TP
in
.IR _res.options .
This enables support for the DNS extensions described in RFC\ 2671.
+.TP
+.BR single-request " (since glibc 2.10)"
+sets
+.BR RES_SNGLKUP
+in
+.IR _res.options .
+By default, glibc performs IPv4 and IPv6 lookups in parallel since
+version 2.9.
+Some appliance DNS servers
+cannot handle these queries properly and make the requests time out.
+This option disables the behavior and makes glibc perform the IPv6
+and IPv4 requests sequentially (at the cost of some slowdown of the
+resolving process).
+.TP
+.BR single-request-reopen " (since glibc 2.9)"
+The resolver uses the same socket for the A and AAAA requests.
+Some hardware mistakenly sends back only one reply.
+When that happens the client system will sit and wait for the second reply.
+Turning this option on changes this behavior
+so that if two requests from the same port are not handled correctly it will
+close the socket and open a new one before sending the second request.
+.TP
+.BR no-tld-query " (since glibc 2.14)"
+sets RES_NOTLDQUERY in
+.IR _res.options .
+This option causes
+.BR res_nsearch ()
+to not attempt to resolve an unqualified name
+as if it were a top level domain (TLD).
+This option can cause problems if the site has ``localhost'' as a TLD
+rather than having localhost on one or more elements of the search list.
+This option has no effect if neither RES_DEFNAMES or RES_DNSRCH is set.
.RE
.LP
The \fIdomain\fP and \fIsearch\fP keywords are mutually exclusive.
.SH FILES
.IR /etc/resolv.conf ,
.I <resolv.h>
-.SH "SEE ALSO"
+.SH SEE ALSO
.BR gethostbyname (3),
.BR resolver (3),
.BR hostname (7),
.BR named (8)
.br
Name Server Operations Guide for BIND
+.SH COLOPHON
+This page is part of release 3.79 of the Linux
+.I man-pages
+project.
+A description of the project,
+information about reporting bugs,
+and the latest version of this page,
+can be found at
+\%http://www.kernel.org/doc/man\-pages/.
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