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7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen - Copyright (C) 2004-2009 Internet Systems Consortium, Inc. ("ISC")
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen - Copyright (C) 2000-2003 Internet Software Consortium.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen - Permission to use, copy, modify, and distribute this software for any
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen - purpose with or without fee is hereby granted, provided that the above
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen - copyright notice and this permission notice appear in all copies.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen - THE SOFTWARE IS PROVIDED "AS IS" AND ISC DISCLAIMS ALL WARRANTIES WITH
b039dabf4c53f72454e795930e7643b6e0e625f9Timo Sirainen - REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen - AND FITNESS. IN NO EVENT SHALL ISC BE LIABLE FOR ANY SPECIAL, DIRECT,
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen - INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen - LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
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11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen<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>
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen<p><span><strong class="command">host</strong></span>
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen is a simple utility for performing DNS lookups.
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen It is normally used to convert names to IP addresses and vice versa.
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen When no arguments or options are given,
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen <span><strong class="command">host</strong></span>
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen prints a short summary of its command line arguments and options.
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen<p><em class="parameter"><code>name</code></em> is the domain name that is to be
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen up. It can also be a dotted-decimal IPv4 address or a colon-delimited
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen IPv6 address, in which case <span><strong class="command">host</strong></span> will by
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen perform a reverse lookup for that address.
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen <em class="parameter"><code>server</code></em> is an optional argument which
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen the name or IP address of the name server that <span><strong class="command">host</strong></span>
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen should query instead of the server or servers listed in
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen <code class="filename">/etc/resolv.conf</code>.
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen The <code class="option">-a</code> (all) option is equivalent to setting the
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen <code class="option">-v</code> option and asking <span><strong class="command">host</strong></span> to make
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen a query of type ANY.
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen When the <code class="option">-C</code> option is used, <span><strong class="command">host</strong></span>
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen will attempt to display the SOA records for zone
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen <em class="parameter"><code>name</code></em> from all the listed
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen authoritative name
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen servers for that zone. The list of name servers is defined by the NS
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen records that are found for the zone.
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen The <code class="option">-c</code> option instructs to make a DNS query of class
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen <em class="parameter"><code>class</code></em>. This can be used to lookup
11fec79522fc0cebe7321d1a9206568d22ddc1c0Timo Sirainen Chaosnet class resource records. The default class is IN (Internet).
f428ea9564d72894c18b8f3876bfaaf677ce19aaTimo Sirainen Verbose output is generated by <span><strong class="command">host</strong></span> when
f428ea9564d72894c18b8f3876bfaaf677ce19aaTimo Sirainen <code class="option">-d</code> or <code class="option">-v</code> option is used. The two
f428ea9564d72894c18b8f3876bfaaf677ce19aaTimo Sirainen options are equivalent. They have been provided for backwards
f428ea9564d72894c18b8f3876bfaaf677ce19aaTimo Sirainen compatibility. In previous versions, the <code class="option">-d</code> option
f428ea9564d72894c18b8f3876bfaaf677ce19aaTimo Sirainen switched on debugging traces and <code class="option">-v</code> enabled verbose
f428ea9564d72894c18b8f3876bfaaf677ce19aaTimo Sirainen List mode is selected by the <code class="option">-l</code> option. This makes
f428ea9564d72894c18b8f3876bfaaf677ce19aaTimo Sirainen <span><strong class="command">host</strong></span> perform a zone transfer for zone
f428ea9564d72894c18b8f3876bfaaf677ce19aaTimo Sirainen <em class="parameter"><code>name</code></em>. Transfer the zone printing out
f428ea9564d72894c18b8f3876bfaaf677ce19aaTimo Sirainen and address records (A/AAAA). If combined with <code class="option">-a</code>
f428ea9564d72894c18b8f3876bfaaf677ce19aaTimo Sirainen all records will be printed.
f428ea9564d72894c18b8f3876bfaaf677ce19aaTimo Sirainen option specifies that reverse lookups of IPv6 addresses should
f428ea9564d72894c18b8f3876bfaaf677ce19aaTimo Sirainen use the IP6.INT domain as defined in RFC1886.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen The default is to use IP6.ARPA.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen The <code class="option">-N</code> option sets the number of dots that have to be
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen in <em class="parameter"><code>name</code></em> for it to be considered
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen absolute. The
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen default value is that defined using the ndots statement in
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <code class="filename">/etc/resolv.conf</code>, or 1 if no ndots
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen present. Names with fewer dots are interpreted as relative names and
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen will be searched for in the domains listed in the <span class="type">search</span>
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen or <span class="type">domain</span> directive in
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <code class="filename">/etc/resolv.conf</code>.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen The number of UDP retries for a lookup can be changed with the
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <code class="option">-R</code> option. <em class="parameter"><code>number</code></em>
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen how many times <span><strong class="command">host</strong></span> will repeat a query
12ef7b394dfdf4d53d432ac576f6bfcd20ebad6dTimo Sirainen not get answered. The default number of retries is 1. If
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <em class="parameter"><code>number</code></em> is negative or zero, the
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen retries will default to 1.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen Non-recursive queries can be made via the <code class="option">-r</code> option.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen Setting this option clears the <span class="type">RD</span> — recursion
8e371a3ce32bd64288786855b8ce0cb63f19f7d1Timo Sirainen desired — bit in the query which <span><strong class="command">host</strong></span> makes.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen This should mean that the name server receiving the query will not
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen attempt to resolve <em class="parameter"><code>name</code></em>. The
12ef7b394dfdf4d53d432ac576f6bfcd20ebad6dTimo Sirainen <code class="option">-r</code> option enables <span><strong class="command">host</strong></span>
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen the behavior of a name server by making non-recursive queries and
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen expecting to receive answers to those queries that are usually
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen referrals to other name servers.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen By default, <span><strong class="command">host</strong></span> uses UDP when making
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <code class="option">-T</code> option makes it use a TCP connection when querying
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen the name server. TCP will be automatically selected for queries that
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen require it, such as zone transfer (AXFR) requests.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen The <code class="option">-4</code> option forces <span><strong class="command">host</strong></span> to only
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen use IPv4 query transport. The <code class="option">-6</code> option forces
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <span><strong class="command">host</strong></span> to only use IPv6 query transport.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen The <code class="option">-t</code> option is used to select the query type.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <em class="parameter"><code>type</code></em> can be any recognized query
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen NS, SOA, SIG, KEY, AXFR, etc. When no query type is specified,
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <span><strong class="command">host</strong></span> automatically selects an appropriate
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen type. By default, it looks for A, AAAA, and MX records, but if the
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <code class="option">-C</code> option was given, queries will be made for SOA
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen records, and if <em class="parameter"><code>name</code></em> is a
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen dotted-decimal IPv4
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen address or colon-delimited IPv6 address, <span><strong class="command">host</strong></span> will
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen query for PTR records. If a query type of IXFR is chosen the starting
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen serial number can be specified by appending an equal followed by the
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen starting serial number (e.g. -t IXFR=12345678).
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen The time to wait for a reply can be controlled through the
8e371a3ce32bd64288786855b8ce0cb63f19f7d1Timo Sirainen <code class="option">-W</code> and <code class="option">-w</code> options. The
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <code class="option">-W</code> option makes <span><strong class="command">host</strong></span>
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <em class="parameter"><code>wait</code></em> seconds. If <em class="parameter"><code>wait</code></em>
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen is less than one, the wait interval is set to one second. When the
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <code class="option">-w</code> option is used, <span><strong class="command">host</strong></span>
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen effectively wait forever for a reply. The time to wait for a response
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen will be set to the number of seconds given by the hardware's maximum
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen value for an integer quantity.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen The <code class="option">-s</code> option tells <span><strong class="command">host</strong></span>
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <span class="emphasis"><em>not</em></span> to send the query to the next nameserver
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen if any server responds with a SERVFAIL response, which is the
8e371a3ce32bd64288786855b8ce0cb63f19f7d1Timo Sirainen reverse of normal stub resolver behavior.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen The <code class="option">-m</code> can be used to set the memory usage debugging
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <em class="parameter"><code>record</code></em>, <em class="parameter"><code>usage</code></em> and
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <em class="parameter"><code>trace</code></em>.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen If <span><strong class="command">host</strong></span> has been built with IDN (internationalized
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen domain name) support, it can accept and display non-ASCII domain names.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <span><strong class="command">host</strong></span> appropriately converts character encoding of
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen domain name before sending a request to DNS server or displaying a
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen reply from the server.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen If you'd like to turn off the IDN support for some reason, defines
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen the <code class="envar">IDN_DISABLE</code> environment variable.
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen The IDN support is disabled if the variable is set when
8e371a3ce32bd64288786855b8ce0cb63f19f7d1Timo Sirainen <span><strong class="command">host</strong></span> runs.
8e371a3ce32bd64288786855b8ce0cb63f19f7d1Timo Sirainen<p><code class="filename">/etc/resolv.conf</code>
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen<p><span class="citerefentry"><span class="refentrytitle">dig</span>(1)</span>,
7fb70daba4e571eab5b64f496d20b9e37e31141bTimo Sirainen <span class="citerefentry"><span class="refentrytitle">named</span>(8)</span>.
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