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diff --git a/man5/resolv.conf.5 b/man5/resolv.conf.5 new file mode 100644 index 000000000..dac44f702 --- /dev/null +++ b/man5/resolv.conf.5 @@ -0,0 +1,195 @@ +.\" Copyright (c) 1986 The Regents of the University of California. +.\" All rights reserved. +.\" +.\" 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, +.\" advertising materials, and other materials related to such +.\" distribution and use acknowledge that the software was developed +.\" by the University of California, Berkeley. The name of the +.\" University may not be used to endorse or promote products derived +.\" from this software without specific prior written permission. +.\" 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. +.\" +.\" @(#)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 2004-10-31 +.UC 4 +.SH NAME +resolv.conf \- resolver configuration file +.SH SYNOPSIS +/etc/resolv.conf +.SH DESCRIPTION +The +.I resolver +is a set of routines in the C library +that provide access to the Internet Domain Name System (DNS). +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. +.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; +the domain name is determined from the host name +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. +Up to MAXNS (currently 3, see <resolv.h>) name servers may be listed, +one per keyword. +If there are multiple servers, +the resolver library queries them in the order listed. +If no \fBnameserver\fP 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.) +.TP +\fBdomain\fP Local domain name. +Most queries for names within this domain can use short names +relative to the local domain. +If no \fBdomain\fP entry is present, the domain is determined +from the local host name returned by +\fIgethostname\fP(); +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. +.TP +\fBsearch\fP Search list for host-name lookup. +The search list is normally determined from the local domain name; +by default, it contains only the local domain name. +This may be changed by listing the desired domain search path +following the \fIsearch\fP keyword with spaces or tabs separating +the names. +Resolver queries having fewer than +.I ndots +dots (default is 1) in them will be attempted using each component +of the search path in turn until a match is found. +For environments with multiple subdomains please read +.BI "options ndots:" n +below to avoid man-in-the-middle attacks and unnecessary +traffic for the root-dns-servers. +.\" When having a resolv.conv with a line +.\" search subdomain.domain.tld domain.tld +.\" and doing a hostlookup, for example by +.\" ping host.anothersubdomain +.\" it sends dns-requests for +.\" host.anothersubdomain. +.\" host.anothersubdomain.subdomain.domain.tld. +.\" host.anothersubdomain.domain.tld. +.\" thus not only causing unnecessary traffic for the root-dns-servers +.\" but broadcasting information to the outside and making man-in-the-middle +.\" attacks possible. +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. +.IP +The search list is currently limited to six domains +with a total of 256 characters. +.TP +\fBsortlist\fP +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 separated by slashes. Up to 10 pairs may +be specified. E.g., +.br +.in +2 +sortlist 130.155.160.0/255.255.240.0 130.155.0.0 +.in -2 +.br +.TP +\fBoptions\fP +Options allows certain internal resolver variables to be modified. +The syntax is +.RS +.IP +\fBoptions\fP \fIoption\fP \fI...\fP +.LP +where \fIoption\fP is one of the following: +.TP +\fBdebug\fP +sets RES_DEBUG in +.IR _res.options . +.TP +.BI ndots: n +sets a threshold for the number of dots which +must appear in a name given to \fBres_query\fP() (see +.BR resolver (3)) +before an \fIinitial absolute query\fP will be made. The default for +\fIn\fP is ``1'', meaning that if there are any dots in a name, the name +will be tried first as an absolute name before any \fIsearch list\fP +elements are appended to it. +.TP +.BI timeout: n +sets the amount of time the resolver will wait for a +response from a remote name server before retrying the +query via a different name server. Measured in seconds, +the default is RES_TIMEOUT (currently 5, see <resolv.h>). +.TP +.BI attempts: n +sets the number of times the resolver will send a +query to its name servers before giving up and returning +an error to the calling application. The default +is RES_DFLRETRY (currently 2, see <resolv.h>). +.TP +.B rotate +sets RES_ROTATE in +.IR _res.options , +which causes round robin selection of nameservers 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 +.B no-check-names +sets RES_NOCHECKNAME in +.IR _res.options , +which disables the modern BIND checking of incoming host names and +mail names for invalid characters such as underscore (_), non-ASCII, +or control characters. +.TP +.B inet6 +sets RES_USE_INET6 in +.IR _res.options . +This has the effect of trying a AAAA query before an A query inside the +.IR gethostbyname () +function, and of mapping IPv4 responses in IPv6 ``tunnelled form'' +if no AAAA records are found but an A record set exists. +.RE +.LP +The \fIdomain\fP and \fIsearch\fP keywords are mutually exclusive. +If more than one instance of these keywords is present, +the last instance wins. +.LP +The \fIsearch\fP keyword of a system's \fIresolv.conf\fP file can be +overridden on a per-process basis by setting the environment variable +``\s-1LOCALDOMAIN\s+1'' to a space-separated list of search domains. +.LP +The \fIoptions\fP keyword of a system's \fIresolv.conf\fP file can be +amended on a per-process basis by setting the environment variable +``\s-1RES_OPTIONS\s+1'' to a space-separated list of resolver options +as explained above under \fBoptions\fP. +.LP +The keyword and value must appear on a single line, and the keyword +(e.g. \fBnameserver\fP) must start the line. The value follows +the keyword, separated by white space. +.SH FILES +.IR /etc/resolv.conf , +.I <resolv.h> +.SH "SEE ALSO" +.BR gethostbyname (3), +.BR resolver (3), +.BR hostname (7), +.BR named (8) +.br +Name Server Operations Guide for BIND |