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9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington - Copyright (C) 2004-2006 Internet Systems Consortium, Inc. ("ISC")
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington - Copyright (C) 2000-2003 Internet Software Consortium.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington - Permission to use, copy, modify, and distribute this software for any
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington - purpose with or without fee is hereby granted, provided that the above
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington - copyright notice and this permission notice appear in all copies.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington - THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington - REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington - AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington - INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington - LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
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9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington<tr><th colspan="3" align="center">host</th></tr>
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9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington<a name="man.host"></a><div class="titlepage"></div>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington<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>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington<a name="id2597700"></a><h2>DESCRIPTION</h2>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington<p><span><strong class="command">host</strong></span>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington is a simple utility for performing DNS lookups.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington It is normally used to convert names to IP addresses and vice versa.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington When no arguments or options are given,
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <span><strong class="command">host</strong></span>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington prints a short summary of its command line arguments and options.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington<p><em class="parameter"><code>name</code></em> is the domain name that is to be
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington up. It can also be a dotted-decimal IPv4 address or a colon-delimited
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington IPv6 address, in which case <span><strong class="command">host</strong></span> will by
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington perform a reverse lookup for that address.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <em class="parameter"><code>server</code></em> is an optional argument which
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington the name or IP address of the name server that <span><strong class="command">host</strong></span>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington should query instead of the server or servers listed in
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <code class="filename">/etc/resolv.conf</code>.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington The <code class="option">-a</code> (all) option is equivalent to setting the
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <code class="option">-v</code> option and asking <span><strong class="command">host</strong></span> to make
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington a query of type ANY.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington When the <code class="option">-C</code> option is used, <span><strong class="command">host</strong></span>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington will attempt to display the SOA records for zone
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <em class="parameter"><code>name</code></em> from all the listed
6ec499054450c5e0fd69d78961deef46985ba363Brian Wellington authoritative name
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington servers for that zone. The list of name servers is defined by the NS
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington records that are found for the zone.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington The <code class="option">-c</code> option instructs to make a DNS query of class
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <em class="parameter"><code>class</code></em>. This can be used to lookup
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington Chaosnet class resource records. The default class is IN (Internet).
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington Verbose output is generated by <span><strong class="command">host</strong></span> when
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <code class="option">-d</code> or <code class="option">-v</code> option is used. The two
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington options are equivalent. They have been provided for backwards
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington compatibility. In previous versions, the <code class="option">-d</code> option
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington switched on debugging traces and <code class="option">-v</code> enabled verbose
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington List mode is selected by the <code class="option">-l</code> option. This makes
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <span><strong class="command">host</strong></span> perform a zone transfer for zone
6ec499054450c5e0fd69d78961deef46985ba363Brian Wellington <em class="parameter"><code>name</code></em>. Transfer the zone printing out
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington and address records (A/AAAA). If combined with <code class="option">-a</code>
6ec499054450c5e0fd69d78961deef46985ba363Brian Wellington all records will be printed.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington option specifies that reverse lookups of IPv6 addresses should
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington use the IP6.INT domain as defined in RFC1886.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington The default is to use IP6.ARPA.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington The <code class="option">-N</code> option sets the number of dots that have to be
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington in <em class="parameter"><code>name</code></em> for it to be considered
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington absolute. The
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington default value is that defined using the ndots statement in
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <code class="filename">/etc/resolv.conf</code>, or 1 if no ndots
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington present. Names with fewer dots are interpreted as relative names and
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington will be searched for in the domains listed in the <span class="type">search</span>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington or <span class="type">domain</span> directive in
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <code class="filename">/etc/resolv.conf</code>.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington The number of UDP retries for a lookup can be changed with the
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <code class="option">-R</code> option. <em class="parameter"><code>number</code></em>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington how many times <span><strong class="command">host</strong></span> will repeat a query
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington not get answered. The default number of retries is 1. If
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <em class="parameter"><code>number</code></em> is negative or zero, the
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington retries will default to 1.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington Non-recursive queries can be made via the <code class="option">-r</code> option.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington Setting this option clears the <span class="type">RD</span> — recursion
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington desired — bit in the query which <span><strong class="command">host</strong></span> makes.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington This should mean that the name server receiving the query will not
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington attempt to resolve <em class="parameter"><code>name</code></em>. The
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <code class="option">-r</code> option enables <span><strong class="command">host</strong></span>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington the behaviour of a name server by making non-recursive queries and
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington expecting to receive answers to those queries that are usually
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington referrals to other name servers.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington By default <span><strong class="command">host</strong></span> uses UDP when making
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <code class="option">-T</code> option makes it use a TCP connection when querying
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington the name server. TCP will be automatically selected for queries that
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington require it, such as zone transfer (AXFR) requests.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington The <code class="option">-4</code> option forces <span><strong class="command">host</strong></span> to only
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington use IPv4 query transport. The <code class="option">-6</code> option forces
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <span><strong class="command">host</strong></span> to only use IPv6 query transport.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington The <code class="option">-t</code> option is used to select the query type.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <em class="parameter"><code>type</code></em> can be any recognised query
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington NS, SOA, SIG, KEY, AXFR, etc. When no query type is specified,
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <span><strong class="command">host</strong></span> automatically selects an appropriate
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington type. By default it looks for A records, but if the
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <code class="option">-C</code> option was given, queries will be made for SOA
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington records, and if <em class="parameter"><code>name</code></em> is a
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington dotted-decimal IPv4
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington address or colon-delimited IPv6 address, <span><strong class="command">host</strong></span> will
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington query for PTR records. If a query type of IXFR is chosen the starting
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington serial number can be specified by appending an equal followed by the
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington starting serial number (e.g. -t IXFR=12345678).
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington The time to wait for a reply can be controlled through the
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <code class="option">-W</code> and <code class="option">-w</code> options. The
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <code class="option">-W</code> option makes <span><strong class="command">host</strong></span>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <em class="parameter"><code>wait</code></em> seconds. If <em class="parameter"><code>wait</code></em>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington is less than one, the wait interval is set to one second. When the
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <code class="option">-w</code> option is used, <span><strong class="command">host</strong></span>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington effectively wait forever for a reply. The time to wait for a response
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington will be set to the number of seconds given by the hardware's maximum
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington value for an integer quantity.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington The <code class="option">-s</code> option tells <span><strong class="command">host</strong></span>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <span class="emphasis"><em>not</em></span> to send the query to the next nameserver
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington if any server responds with a SERVFAIL response, which is the
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington reverse of normal stub resolver behaviour.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington The <code class="option">-m</code> can be used to set the memory usage debugging
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <em class="parameter"><code>record</code></em>, <em class="parameter"><code>usage</code></em> and
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <em class="parameter"><code>trace</code></em>.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington<a name="id2598282"></a><h2>IDN SUPPORT</h2>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington If <span><strong class="command">host</strong></span> has been built with IDN (internationalized
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington domain name) support, it can accept and display non-ASCII domain names.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <span><strong class="command">host</strong></span> appropriately converts character encoding of
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington domain name before sending a request to DNS server or displaying a
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington reply from the server.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington If you'd like to turn off the IDN support for some reason, defines
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington the <code class="envar">IDN_DISABLE</code> environment variable.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington The IDN support is disabled if the variable is set when
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <span><strong class="command">host</strong></span> runs.
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington<p><code class="filename">/etc/resolv.conf</code>
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington<p><span class="citerefentry"><span class="refentrytitle">dig</span>(1)</span>,
9e3a7b0faf417a10f5f689edf288807b2d5eedc5Brian Wellington <span class="citerefentry"><span class="refentrytitle">named</span>(8)</span>.
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