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6029a2d88c01674debfd7c2e16c941a97302b739susans - Copyright (C) 2004-2014 Internet Systems Consortium, Inc. ("ISC")
6029a2d88c01674debfd7c2e16c941a97302b739susans - Copyright (C) 2000-2003 Internet Software Consortium.
6029a2d88c01674debfd7c2e16c941a97302b739susans - Permission to use, copy, modify, and/or distribute this software for any
6029a2d88c01674debfd7c2e16c941a97302b739susans - purpose with or without fee is hereby granted, provided that the above
6029a2d88c01674debfd7c2e16c941a97302b739susans - copyright notice and this permission notice appear in all copies.
6029a2d88c01674debfd7c2e16c941a97302b739susans - THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
6029a2d88c01674debfd7c2e16c941a97302b739susans - REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
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6029a2d88c01674debfd7c2e16c941a97302b739susans<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>] [<code class="option">-v</code>] [<code class="option">-V</code>] {name} [server]</p></div>
6029a2d88c01674debfd7c2e16c941a97302b739susans is a simple utility for performing DNS lookups.
6029a2d88c01674debfd7c2e16c941a97302b739susans It is normally used to convert names to IP addresses and vice versa.
6029a2d88c01674debfd7c2e16c941a97302b739susans When no arguments or options are given,
6029a2d88c01674debfd7c2e16c941a97302b739susans prints a short summary of its command line arguments and options.
6029a2d88c01674debfd7c2e16c941a97302b739susans<p><em class="parameter"><code>name</code></em> is the domain name that is to be
6029a2d88c01674debfd7c2e16c941a97302b739susans up. It can also be a dotted-decimal IPv4 address or a colon-delimited
6029a2d88c01674debfd7c2e16c941a97302b739susans IPv6 address, in which case <span><strong class="command">host</strong></span> will by
6029a2d88c01674debfd7c2e16c941a97302b739susans perform a reverse lookup for that address.
6029a2d88c01674debfd7c2e16c941a97302b739susans <em class="parameter"><code>server</code></em> is an optional argument which
2fa451d9fff38ef869918fcfb1d61717fdb3cf7cYu Wu - Sun Microsystems - Beijing China the name or IP address of the name server that <span><strong class="command">host</strong></span>
2fa451d9fff38ef869918fcfb1d61717fdb3cf7cYu Wu - Sun Microsystems - Beijing China should query instead of the server or servers listed in
2fa451d9fff38ef869918fcfb1d61717fdb3cf7cYu Wu - Sun Microsystems - Beijing China <code class="filename">/etc/resolv.conf</code>.
2fa451d9fff38ef869918fcfb1d61717fdb3cf7cYu Wu - Sun Microsystems - Beijing China The <code class="option">-a</code> (all) option is equivalent to setting the
2fa451d9fff38ef869918fcfb1d61717fdb3cf7cYu Wu - Sun Microsystems - Beijing China <code class="option">-v</code> option and asking <span><strong class="command">host</strong></span> to make
6029a2d88c01674debfd7c2e16c941a97302b739susans a query of type ANY.
6029a2d88c01674debfd7c2e16c941a97302b739susans When the <code class="option">-C</code> option is used, <span><strong class="command">host</strong></span>
6029a2d88c01674debfd7c2e16c941a97302b739susans will attempt to display the SOA records for zone
6029a2d88c01674debfd7c2e16c941a97302b739susans <em class="parameter"><code>name</code></em> from all the listed
6029a2d88c01674debfd7c2e16c941a97302b739susans authoritative name
6029a2d88c01674debfd7c2e16c941a97302b739susans servers for that zone. The list of name servers is defined by the NS
6029a2d88c01674debfd7c2e16c941a97302b739susans records that are found for the zone.
7ddfa2acf3cfb8a6397a0fb7b4dcd2ce701cc293Susan Scheufele The <code class="option">-c</code> option instructs to make a DNS query of class
7ddfa2acf3cfb8a6397a0fb7b4dcd2ce701cc293Susan Scheufele <em class="parameter"><code>class</code></em>. This can be used to lookup
7ddfa2acf3cfb8a6397a0fb7b4dcd2ce701cc293Susan Scheufele Chaosnet class resource records. The default class is IN (Internet).
7ddfa2acf3cfb8a6397a0fb7b4dcd2ce701cc293Susan Scheufele Verbose output is generated by <span><strong class="command">host</strong></span> when
7ddfa2acf3cfb8a6397a0fb7b4dcd2ce701cc293Susan Scheufele <code class="option">-d</code> or <code class="option">-v</code> option is used. The two
7ddfa2acf3cfb8a6397a0fb7b4dcd2ce701cc293Susan Scheufele options are equivalent. They have been provided for backwards
7ddfa2acf3cfb8a6397a0fb7b4dcd2ce701cc293Susan Scheufele compatibility. In previous versions, the <code class="option">-d</code> option
7ddfa2acf3cfb8a6397a0fb7b4dcd2ce701cc293Susan Scheufele switched on debugging traces and <code class="option">-v</code> enabled verbose
6029a2d88c01674debfd7c2e16c941a97302b739susans output. Verbose output can also be enabled by setting the
6029a2d88c01674debfd7c2e16c941a97302b739susans <em class="parameter"><code>debug</code></em> option in
6029a2d88c01674debfd7c2e16c941a97302b739susans List mode is selected by the <code class="option">-l</code> option. This makes
6029a2d88c01674debfd7c2e16c941a97302b739susans <span><strong class="command">host</strong></span> perform a zone transfer for zone
6029a2d88c01674debfd7c2e16c941a97302b739susans <em class="parameter"><code>name</code></em>. Transfer the zone printing out
6029a2d88c01674debfd7c2e16c941a97302b739susans the NS, PTR
6029a2d88c01674debfd7c2e16c941a97302b739susans and address records (A/AAAA). If combined with <code class="option">-a</code>
6029a2d88c01674debfd7c2e16c941a97302b739susans all records will be printed.
6029a2d88c01674debfd7c2e16c941a97302b739susans option specifies that reverse lookups of IPv6 addresses should
6029a2d88c01674debfd7c2e16c941a97302b739susans use the IP6.INT domain as defined in RFC1886.
6029a2d88c01674debfd7c2e16c941a97302b739susans The default is to use IP6.ARPA.
6029a2d88c01674debfd7c2e16c941a97302b739susans The <code class="option">-N</code> option sets the number of dots that have to be
6029a2d88c01674debfd7c2e16c941a97302b739susans in <em class="parameter"><code>name</code></em> for it to be considered
6029a2d88c01674debfd7c2e16c941a97302b739susans absolute. The
6029a2d88c01674debfd7c2e16c941a97302b739susans default value is that defined using the ndots statement in
6029a2d88c01674debfd7c2e16c941a97302b739susans <code class="filename">/etc/resolv.conf</code>, or 1 if no ndots
6029a2d88c01674debfd7c2e16c941a97302b739susans statement is
6029a2d88c01674debfd7c2e16c941a97302b739susans present. Names with fewer dots are interpreted as relative names and
6029a2d88c01674debfd7c2e16c941a97302b739susans will be searched for in the domains listed in the <span class="type">search</span>
6029a2d88c01674debfd7c2e16c941a97302b739susans The number of UDP retries for a lookup can be changed with the
6029a2d88c01674debfd7c2e16c941a97302b739susans <code class="option">-R</code> option. <em class="parameter"><code>number</code></em>
6029a2d88c01674debfd7c2e16c941a97302b739susans how many times <span><strong class="command">host</strong></span> will repeat a query
6029a2d88c01674debfd7c2e16c941a97302b739susans not get answered. If
6029a2d88c01674debfd7c2e16c941a97302b739susans <em class="parameter"><code>number</code></em> is negative or zero, the
6029a2d88c01674debfd7c2e16c941a97302b739susans retries will default to 1. The default value is 1, or
6029a2d88c01674debfd7c2e16c941a97302b739susans the value of the <em class="parameter"><code>attempts</code></em> option in
193974072f41a843678abf5f61979c748687e66bSherry Moore <code class="filename">/etc/resolv.conf</code>, if set.
6029a2d88c01674debfd7c2e16c941a97302b739susans Non-recursive queries can be made via the <code class="option">-r</code> option.
6029a2d88c01674debfd7c2e16c941a97302b739susans Setting this option clears the <span class="type">RD</span> — recursion
6029a2d88c01674debfd7c2e16c941a97302b739susans desired — bit in the query which <span><strong class="command">host</strong></span> makes.
6029a2d88c01674debfd7c2e16c941a97302b739susans This should mean that the name server receiving the query will not
6029a2d88c01674debfd7c2e16c941a97302b739susans attempt to resolve <em class="parameter"><code>name</code></em>. The
6029a2d88c01674debfd7c2e16c941a97302b739susans <code class="option">-r</code> option enables <span><strong class="command">host</strong></span>
6029a2d88c01674debfd7c2e16c941a97302b739susans the behavior of a name server by making non-recursive queries and
6029a2d88c01674debfd7c2e16c941a97302b739susans expecting to receive answers to those queries that are usually
6029a2d88c01674debfd7c2e16c941a97302b739susans referrals to other name servers.
6029a2d88c01674debfd7c2e16c941a97302b739susans By default, <span><strong class="command">host</strong></span> uses UDP when making
6029a2d88c01674debfd7c2e16c941a97302b739susans queries. The
6029a2d88c01674debfd7c2e16c941a97302b739susans <code class="option">-T</code> option makes it use a TCP connection when querying
6029a2d88c01674debfd7c2e16c941a97302b739susans the name server. TCP will be automatically selected for queries that
6029a2d88c01674debfd7c2e16c941a97302b739susans require it, such as zone transfer (AXFR) requests.
6029a2d88c01674debfd7c2e16c941a97302b739susans The <code class="option">-4</code> option forces <span><strong class="command">host</strong></span> to only
6029a2d88c01674debfd7c2e16c941a97302b739susans use IPv4 query transport. The <code class="option">-6</code> option forces
6029a2d88c01674debfd7c2e16c941a97302b739susans <span><strong class="command">host</strong></span> to only use IPv6 query transport.
6029a2d88c01674debfd7c2e16c941a97302b739susans The <code class="option">-t</code> option is used to select the query type.
6029a2d88c01674debfd7c2e16c941a97302b739susans <em class="parameter"><code>type</code></em> can be any recognized query
6029a2d88c01674debfd7c2e16c941a97302b739susans type: CNAME,
6029a2d88c01674debfd7c2e16c941a97302b739susans NS, SOA, SIG, KEY, AXFR, etc. When no query type is specified,
6029a2d88c01674debfd7c2e16c941a97302b739susans <span><strong class="command">host</strong></span> automatically selects an appropriate
6029a2d88c01674debfd7c2e16c941a97302b739susans type. By default, it looks for A, AAAA, and MX records, but if the
6029a2d88c01674debfd7c2e16c941a97302b739susans <code class="option">-C</code> option was given, queries will be made for SOA
6029a2d88c01674debfd7c2e16c941a97302b739susans records, and if <em class="parameter"><code>name</code></em> is a
6029a2d88c01674debfd7c2e16c941a97302b739susans dotted-decimal IPv4
6029a2d88c01674debfd7c2e16c941a97302b739susans address or colon-delimited IPv6 address, <span><strong class="command">host</strong></span> will
6029a2d88c01674debfd7c2e16c941a97302b739susans query for PTR records. If a query type of IXFR is chosen the starting
6029a2d88c01674debfd7c2e16c941a97302b739susans serial number can be specified by appending an equal followed by the
6029a2d88c01674debfd7c2e16c941a97302b739susans starting serial number (e.g. -t IXFR=12345678).
6029a2d88c01674debfd7c2e16c941a97302b739susans The time to wait for a reply can be controlled through the
6029a2d88c01674debfd7c2e16c941a97302b739susans <code class="option">-W</code> and <code class="option">-w</code> options. The
6029a2d88c01674debfd7c2e16c941a97302b739susans <code class="option">-W</code> option makes <span><strong class="command">host</strong></span>
6029a2d88c01674debfd7c2e16c941a97302b739susans <em class="parameter"><code>wait</code></em> seconds. If <em class="parameter"><code>wait</code></em>
6029a2d88c01674debfd7c2e16c941a97302b739susans is less than one, the wait interval is set to one second. When the
6029a2d88c01674debfd7c2e16c941a97302b739susans <code class="option">-w</code> option is used, <span><strong class="command">host</strong></span>
6029a2d88c01674debfd7c2e16c941a97302b739susans effectively wait forever for a reply. The time to wait for a response
6029a2d88c01674debfd7c2e16c941a97302b739susans will be set to the number of seconds given by the hardware's maximum
6029a2d88c01674debfd7c2e16c941a97302b739susans value for an integer quantity. By default, <span><strong class="command">host</strong></span>
6029a2d88c01674debfd7c2e16c941a97302b739susans will wait for 5 seconds for UDP responses and 10 seconds for TCP
6029a2d88c01674debfd7c2e16c941a97302b739susans connections. These defaults can be overridden by the
6029a2d88c01674debfd7c2e16c941a97302b739susans <em class="parameter"><code>timeout</code></em> option in
6029a2d88c01674debfd7c2e16c941a97302b739susans The <code class="option">-s</code> option tells <span><strong class="command">host</strong></span>
6029a2d88c01674debfd7c2e16c941a97302b739susans <span class="emphasis"><em>not</em></span> to send the query to the next nameserver
6029a2d88c01674debfd7c2e16c941a97302b739susans if any server responds with a SERVFAIL response, which is the
6029a2d88c01674debfd7c2e16c941a97302b739susans reverse of normal stub resolver behavior.
6029a2d88c01674debfd7c2e16c941a97302b739susans The <code class="option">-m</code> can be used to set the memory usage debugging
6029a2d88c01674debfd7c2e16c941a97302b739susans <em class="parameter"><code>record</code></em>, <em class="parameter"><code>usage</code></em> and
6029a2d88c01674debfd7c2e16c941a97302b739susans The <code class="option">-V</code> option causes <span><strong class="command">host</strong></span>
6029a2d88c01674debfd7c2e16c941a97302b739susans to print the version number and exit.
6029a2d88c01674debfd7c2e16c941a97302b739susans If <span><strong class="command">host</strong></span> has been built with IDN (internationalized
6029a2d88c01674debfd7c2e16c941a97302b739susans domain name) support, it can accept and display non-ASCII domain names.
6029a2d88c01674debfd7c2e16c941a97302b739susans <span><strong class="command">host</strong></span> appropriately converts character encoding of
6029a2d88c01674debfd7c2e16c941a97302b739susans domain name before sending a request to DNS server or displaying a
6029a2d88c01674debfd7c2e16c941a97302b739susans reply from the server.
6029a2d88c01674debfd7c2e16c941a97302b739susans If you'd like to turn off the IDN support for some reason, defines
6029a2d88c01674debfd7c2e16c941a97302b739susans the <code class="envar">IDN_DISABLE</code> environment variable.
6029a2d88c01674debfd7c2e16c941a97302b739susans The IDN support is disabled if the variable is set when
6029a2d88c01674debfd7c2e16c941a97302b739susans <span><strong class="command">host</strong></span> runs.
6029a2d88c01674debfd7c2e16c941a97302b739susans<p><span class="citerefentry"><span class="refentrytitle">dig</span>(1)</span>,
6029a2d88c01674debfd7c2e16c941a97302b739susans <span class="citerefentry"><span class="refentrytitle">named</span>(8)</span>.
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