213 lines
11 KiB
HTML
213 lines
11 KiB
HTML
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- Copyright (C) 2004, 2005, 2007-2009 Internet Systems Consortium, Inc. ("ISC")
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- Copyright (C) 2000-2002 Internet Software Consortium.
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- Permission to use, copy, modify, and/or distribute this software for any
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
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<title>host</title>
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<meta name="generator" content="DocBook XSL Stylesheets V1.71.1">
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</head>
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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry" lang="en">
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<a name="man.host"></a><div class="titlepage"></div>
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<div class="refnamediv">
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<h2>Name</h2>
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<p>host — DNS lookup utility</p>
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</div>
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<div class="refsynopsisdiv">
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<h2>Synopsis</h2>
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<div class="cmdsynopsis"><p><code class="command">host</code> [<code class="option">-aCdlnrsTwv</code>] [<code class="option">-c <em class="replaceable"><code>class</code></em></code>] [<code class="option">-N <em class="replaceable"><code>ndots</code></em></code>] [<code class="option">-R <em class="replaceable"><code>number</code></em></code>] [<code class="option">-t <em class="replaceable"><code>type</code></em></code>] [<code class="option">-W <em class="replaceable"><code>wait</code></em></code>] [<code class="option">-m <em class="replaceable"><code>flag</code></em></code>] [<code class="option">-4</code>] [<code class="option">-6</code>] {name} [server]</p></div>
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</div>
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<div class="refsect1" lang="en">
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<a name="id2543436"></a><h2>DESCRIPTION</h2>
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<p><span><strong class="command">host</strong></span>
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is a simple utility for performing DNS lookups.
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It is normally used to convert names to IP addresses and vice versa.
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When no arguments or options are given,
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<span><strong class="command">host</strong></span>
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prints a short summary of its command line arguments and options.
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</p>
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<p><em class="parameter"><code>name</code></em> is the domain name that is to be
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looked
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up. It can also be a dotted-decimal IPv4 address or a colon-delimited
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IPv6 address, in which case <span><strong class="command">host</strong></span> will by
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default
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perform a reverse lookup for that address.
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<em class="parameter"><code>server</code></em> is an optional argument which
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is either
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the name or IP address of the name server that <span><strong class="command">host</strong></span>
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should query instead of the server or servers listed in
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<code class="filename">/etc/resolv.conf</code>.
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</p>
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<p>
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The <code class="option">-a</code> (all) option is equivalent to setting the
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<code class="option">-v</code> option and asking <span><strong class="command">host</strong></span> to make
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a query of type ANY.
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</p>
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<p>
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When the <code class="option">-C</code> option is used, <span><strong class="command">host</strong></span>
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will attempt to display the SOA records for zone
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<em class="parameter"><code>name</code></em> from all the listed
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authoritative name
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servers for that zone. The list of name servers is defined by the NS
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records that are found for the zone.
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</p>
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<p>
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The <code class="option">-c</code> option instructs to make a DNS query of class
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<em class="parameter"><code>class</code></em>. This can be used to lookup
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Hesiod or
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Chaosnet class resource records. The default class is IN (Internet).
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</p>
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<p>
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Verbose output is generated by <span><strong class="command">host</strong></span> when
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the
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<code class="option">-d</code> or <code class="option">-v</code> option is used. The two
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options are equivalent. They have been provided for backwards
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compatibility. In previous versions, the <code class="option">-d</code> option
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switched on debugging traces and <code class="option">-v</code> enabled verbose
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output.
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</p>
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<p>
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List mode is selected by the <code class="option">-l</code> option. This makes
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<span><strong class="command">host</strong></span> perform a zone transfer for zone
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<em class="parameter"><code>name</code></em>. Transfer the zone printing out
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the NS, PTR
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and address records (A/AAAA). If combined with <code class="option">-a</code>
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all records will be printed.
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</p>
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<p>
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The <code class="option">-i</code>
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option specifies that reverse lookups of IPv6 addresses should
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use the IP6.INT domain as defined in RFC1886.
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The default is to use IP6.ARPA.
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</p>
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<p>
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The <code class="option">-N</code> option sets the number of dots that have to be
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in <em class="parameter"><code>name</code></em> for it to be considered
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absolute. The
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default value is that defined using the ndots statement in
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<code class="filename">/etc/resolv.conf</code>, or 1 if no ndots
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statement is
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present. Names with fewer dots are interpreted as relative names and
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will be searched for in the domains listed in the <span class="type">search</span>
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or <span class="type">domain</span> directive in
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<code class="filename">/etc/resolv.conf</code>.
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</p>
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<p>
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The number of UDP retries for a lookup can be changed with the
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<code class="option">-R</code> option. <em class="parameter"><code>number</code></em>
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indicates
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how many times <span><strong class="command">host</strong></span> will repeat a query
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that does
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not get answered. The default number of retries is 1. If
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<em class="parameter"><code>number</code></em> is negative or zero, the
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number of
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retries will default to 1.
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</p>
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<p>
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Non-recursive queries can be made via the <code class="option">-r</code> option.
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Setting this option clears the <span class="type">RD</span> — recursion
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desired — bit in the query which <span><strong class="command">host</strong></span> makes.
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This should mean that the name server receiving the query will not
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attempt to resolve <em class="parameter"><code>name</code></em>. The
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<code class="option">-r</code> option enables <span><strong class="command">host</strong></span>
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to mimic
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the behavior of a name server by making non-recursive queries and
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expecting to receive answers to those queries that are usually
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referrals to other name servers.
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</p>
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<p>
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By default, <span><strong class="command">host</strong></span> uses UDP when making
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queries. The
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<code class="option">-T</code> option makes it use a TCP connection when querying
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the name server. TCP will be automatically selected for queries that
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require it, such as zone transfer (AXFR) requests.
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</p>
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<p>
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The <code class="option">-4</code> option forces <span><strong class="command">host</strong></span> to only
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use IPv4 query transport. The <code class="option">-6</code> option forces
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<span><strong class="command">host</strong></span> to only use IPv6 query transport.
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</p>
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<p>
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The <code class="option">-t</code> option is used to select the query type.
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<em class="parameter"><code>type</code></em> can be any recognized query
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type: CNAME,
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NS, SOA, SIG, KEY, AXFR, etc. When no query type is specified,
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<span><strong class="command">host</strong></span> automatically selects an appropriate
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query
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type. By default, it looks for A, AAAA, and MX records, but if the
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<code class="option">-C</code> option was given, queries will be made for SOA
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records, and if <em class="parameter"><code>name</code></em> is a
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dotted-decimal IPv4
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address or colon-delimited IPv6 address, <span><strong class="command">host</strong></span> will
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query for PTR records. If a query type of IXFR is chosen the starting
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serial number can be specified by appending an equal followed by the
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starting serial number (e.g. -t IXFR=12345678).
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</p>
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<p>
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The time to wait for a reply can be controlled through the
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<code class="option">-W</code> and <code class="option">-w</code> options. The
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<code class="option">-W</code> option makes <span><strong class="command">host</strong></span>
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wait for
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<em class="parameter"><code>wait</code></em> seconds. If <em class="parameter"><code>wait</code></em>
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is less than one, the wait interval is set to one second. When the
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<code class="option">-w</code> option is used, <span><strong class="command">host</strong></span>
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will
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effectively wait forever for a reply. The time to wait for a response
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will be set to the number of seconds given by the hardware's maximum
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value for an integer quantity.
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</p>
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<p>
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The <code class="option">-s</code> option tells <span><strong class="command">host</strong></span>
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<span class="emphasis"><em>not</em></span> to send the query to the next nameserver
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if any server responds with a SERVFAIL response, which is the
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reverse of normal stub resolver behavior.
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</p>
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<p>
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The <code class="option">-m</code> can be used to set the memory usage debugging
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flags
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<em class="parameter"><code>record</code></em>, <em class="parameter"><code>usage</code></em> and
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<em class="parameter"><code>trace</code></em>.
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</p>
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</div>
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<div class="refsect1" lang="en">
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<a name="id2543802"></a><h2>IDN SUPPORT</h2>
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<p>
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If <span><strong class="command">host</strong></span> has been built with IDN (internationalized
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domain name) support, it can accept and display non-ASCII domain names.
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<span><strong class="command">host</strong></span> appropriately converts character encoding of
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domain name before sending a request to DNS server or displaying a
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reply from the server.
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If you'd like to turn off the IDN support for some reason, defines
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the <code class="envar">IDN_DISABLE</code> environment variable.
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The IDN support is disabled if the variable is set when
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<span><strong class="command">host</strong></span> runs.
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</p>
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</div>
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<div class="refsect1" lang="en">
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<a name="id2543825"></a><h2>FILES</h2>
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<p><code class="filename">/etc/resolv.conf</code>
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</p>
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</div>
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<div class="refsect1" lang="en">
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<a name="id2543836"></a><h2>SEE ALSO</h2>
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<p><span class="citerefentry"><span class="refentrytitle">dig</span>(1)</span>,
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<span class="citerefentry"><span class="refentrytitle">named</span>(8)</span>.
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</p>
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</div>
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</div></body>
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</html>
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