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a79fe3aad8743ea57e473ea5f66a723244cb9c0eMarkus Roggenbach<!--
8267b99c0d7a187abe6f87ad50530dc08f5d1cdcAndy Gimblett - Copyright (C) 2004-2008 Internet Systems Consortium, Inc. ("ISC")
e071fb22ea9923a2a4ff41184d80ca46b55ee932Till Mossakowski - Copyright (C) 2000-2003 Internet Software Consortium.
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afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett</div>
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett<div class="refentry" lang="en">
e771539425f4a0abef9f94cf4b63690f3603f682Andy Gimblett<a name="man.host"></a><div class="titlepage"></div>
929190acb9f2b2f5857dce841c5a389710895515Andy Gimblett<div class="refnamediv">
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett<h2>Name</h2>
929190acb9f2b2f5857dce841c5a389710895515Andy Gimblett<p>host &#8212; DNS lookup utility</p>
e771539425f4a0abef9f94cf4b63690f3603f682Andy Gimblett</div>
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett<div class="refsynopsisdiv">
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett<h2>Synopsis</h2>
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett<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>
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett</div>
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett<div class="refsect1" lang="en">
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett<a name="id2597954"></a><h2>DESCRIPTION</h2>
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett<p><span><strong class="command">host</strong></span>
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett is a simple utility for performing DNS lookups.
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett It is normally used to convert names to IP addresses and vice versa.
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett When no arguments or options are given,
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett <span><strong class="command">host</strong></span>
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett prints a short summary of its command line arguments and options.
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett </p>
e99df192a380bfa91e3261c911751bb034c09a17Till Mossakowski<p><em class="parameter"><code>name</code></em> is the domain name that is to be
e99df192a380bfa91e3261c911751bb034c09a17Till Mossakowski looked
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett up. It can also be a dotted-decimal IPv4 address or a colon-delimited
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett IPv6 address, in which case <span><strong class="command">host</strong></span> will by
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett default
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett perform a reverse lookup for that address.
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett <em class="parameter"><code>server</code></em> is an optional argument which
eca4db63ed0bdbd93b62678feea6e3eb80aa47bbChristian Maeder is either
1df33829303cbf924aa018ac5ce9a28e69c17d22Till Mossakowski the name or IP address of the name server that <span><strong class="command">host</strong></span>
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett should query instead of the server or servers listed in
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett <code class="filename">/etc/resolv.conf</code>.
1df33829303cbf924aa018ac5ce9a28e69c17d22Till Mossakowski </p>
1df33829303cbf924aa018ac5ce9a28e69c17d22Till Mossakowski<p>
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett The <code class="option">-a</code> (all) option is equivalent to setting the
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett <code class="option">-v</code> option and asking <span><strong class="command">host</strong></span> to make
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett a query of type ANY.
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett </p>
03136b84a0c70d877e227444f0875e209506b9e4Christian Maeder<p>
e771539425f4a0abef9f94cf4b63690f3603f682Andy Gimblett When the <code class="option">-C</code> option is used, <span><strong class="command">host</strong></span>
e771539425f4a0abef9f94cf4b63690f3603f682Andy Gimblett will attempt to display the SOA records for zone
03136b84a0c70d877e227444f0875e209506b9e4Christian Maeder <em class="parameter"><code>name</code></em> from all the listed
b3dca469a9e267d6d71acfdeca7bf284d0581dc7Till Mossakowski authoritative name
e771539425f4a0abef9f94cf4b63690f3603f682Andy Gimblett servers for that zone. The list of name servers is defined by the NS
b3dca469a9e267d6d71acfdeca7bf284d0581dc7Till Mossakowski records that are found for the zone.
03136b84a0c70d877e227444f0875e209506b9e4Christian Maeder </p>
03136b84a0c70d877e227444f0875e209506b9e4Christian Maeder<p>
03136b84a0c70d877e227444f0875e209506b9e4Christian Maeder The <code class="option">-c</code> option instructs to make a DNS query of class
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett <em class="parameter"><code>class</code></em>. This can be used to lookup
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett Hesiod or
1df33829303cbf924aa018ac5ce9a28e69c17d22Till Mossakowski Chaosnet class resource records. The default class is IN (Internet).
b3dca469a9e267d6d71acfdeca7bf284d0581dc7Till Mossakowski </p>
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett<p>
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett Verbose output is generated by <span><strong class="command">host</strong></span> when
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett the
afd6ed16928bbd774b6c6c5b3f440a917dd638a1Andy Gimblett <code class="option">-d</code> or <code class="option">-v</code> option is used. The two
options are equivalent. They have been provided for backwards
compatibility. In previous versions, the <code class="option">-d</code> option
switched on debugging traces and <code class="option">-v</code> enabled verbose
output.
</p>
<p>
List mode is selected by the <code class="option">-l</code> option. This makes
<span><strong class="command">host</strong></span> perform a zone transfer for zone
<em class="parameter"><code>name</code></em>. Transfer the zone printing out
the NS, PTR
and address records (A/AAAA). If combined with <code class="option">-a</code>
all records will be printed.
</p>
<p>
The <code class="option">-i</code>
option specifies that reverse lookups of IPv6 addresses should
use the IP6.INT domain as defined in RFC1886.
The default is to use IP6.ARPA.
</p>
<p>
The <code class="option">-N</code> option sets the number of dots that have to be
in <em class="parameter"><code>name</code></em> for it to be considered
absolute. The
default value is that defined using the ndots statement in
<code class="filename">/etc/resolv.conf</code>, or 1 if no ndots
statement is
present. Names with fewer dots are interpreted as relative names and
will be searched for in the domains listed in the <span class="type">search</span>
or <span class="type">domain</span> directive in
<code class="filename">/etc/resolv.conf</code>.
</p>
<p>
The number of UDP retries for a lookup can be changed with the
<code class="option">-R</code> option. <em class="parameter"><code>number</code></em>
indicates
how many times <span><strong class="command">host</strong></span> will repeat a query
that does
not get answered. The default number of retries is 1. If
<em class="parameter"><code>number</code></em> is negative or zero, the
number of
retries will default to 1.
</p>
<p>
Non-recursive queries can be made via the <code class="option">-r</code> option.
Setting this option clears the <span class="type">RD</span> &#8212; recursion
desired &#8212; bit in the query which <span><strong class="command">host</strong></span> makes.
This should mean that the name server receiving the query will not
attempt to resolve <em class="parameter"><code>name</code></em>. The
<code class="option">-r</code> option enables <span><strong class="command">host</strong></span>
to mimic
the behavior of a name server by making non-recursive queries and
expecting to receive answers to those queries that are usually
referrals to other name servers.
</p>
<p>
By default <span><strong class="command">host</strong></span> uses UDP when making
queries. The
<code class="option">-T</code> option makes it use a TCP connection when querying
the name server. TCP will be automatically selected for queries that
require it, such as zone transfer (AXFR) requests.
</p>
<p>
The <code class="option">-4</code> option forces <span><strong class="command">host</strong></span> to only
use IPv4 query transport. The <code class="option">-6</code> option forces
<span><strong class="command">host</strong></span> to only use IPv6 query transport.
</p>
<p>
The <code class="option">-t</code> option is used to select the query type.
<em class="parameter"><code>type</code></em> can be any recognized query
type: CNAME,
NS, SOA, SIG, KEY, AXFR, etc. When no query type is specified,
<span><strong class="command">host</strong></span> automatically selects an appropriate
query
type. By default it looks for A records, but if the
<code class="option">-C</code> option was given, queries will be made for SOA
records, and if <em class="parameter"><code>name</code></em> is a
dotted-decimal IPv4
address or colon-delimited IPv6 address, <span><strong class="command">host</strong></span> will
query for PTR records. If a query type of IXFR is chosen the starting
serial number can be specified by appending an equal followed by the
starting serial number (e.g. -t IXFR=12345678).
</p>
<p>
The time to wait for a reply can be controlled through the
<code class="option">-W</code> and <code class="option">-w</code> options. The
<code class="option">-W</code> option makes <span><strong class="command">host</strong></span>
wait for
<em class="parameter"><code>wait</code></em> seconds. If <em class="parameter"><code>wait</code></em>
is less than one, the wait interval is set to one second. When the
<code class="option">-w</code> option is used, <span><strong class="command">host</strong></span>
will
effectively wait forever for a reply. The time to wait for a response
will be set to the number of seconds given by the hardware's maximum
value for an integer quantity.
</p>
<p>
The <code class="option">-s</code> option tells <span><strong class="command">host</strong></span>
<span class="emphasis"><em>not</em></span> to send the query to the next nameserver
if any server responds with a SERVFAIL response, which is the
reverse of normal stub resolver behavior.
</p>
<p>
The <code class="option">-m</code> can be used to set the memory usage debugging
flags
<em class="parameter"><code>record</code></em>, <em class="parameter"><code>usage</code></em> and
<em class="parameter"><code>trace</code></em>.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2598400"></a><h2>IDN SUPPORT</h2>
<p>
If <span><strong class="command">host</strong></span> has been built with IDN (internationalized
domain name) support, it can accept and display non-ASCII domain names.
<span><strong class="command">host</strong></span> appropriately converts character encoding of
domain name before sending a request to DNS server or displaying a
reply from the server.
If you'd like to turn off the IDN support for some reason, defines
the <code class="envar">IDN_DISABLE</code> environment variable.
The IDN support is disabled if the variable is set when
<span><strong class="command">host</strong></span> runs.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2598428"></a><h2>FILES</h2>
<p><code class="filename">/etc/resolv.conf</code>
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2598442"></a><h2>SEE ALSO</h2>
<p><span class="citerefentry"><span class="refentrytitle">dig</span>(1)</span>,
<span class="citerefentry"><span class="refentrytitle">named</span>(8)</span>.
</p>
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