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82629e3015252bf18319ba3815c773df23e21436Mike Christensen<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry" lang="en">
82629e3015252bf18319ba3815c773df23e21436Mike Christensen<a name="man.host"></a><div class="titlepage"></div>
82629e3015252bf18319ba3815c773df23e21436Mike Christensen<div class="refnamediv">
82629e3015252bf18319ba3815c773df23e21436Mike Christensen<h2>Name</h2>
82629e3015252bf18319ba3815c773df23e21436Mike Christensen<p>host &#8212; DNS lookup utility</p>
82629e3015252bf18319ba3815c773df23e21436Mike Christensen</div>
82629e3015252bf18319ba3815c773df23e21436Mike Christensen<div class="refsynopsisdiv">
82629e3015252bf18319ba3815c773df23e21436Mike Christensen<h2>Synopsis</h2>
82629e3015252bf18319ba3815c773df23e21436Mike Christensen<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>
82629e3015252bf18319ba3815c773df23e21436Mike Christensen</div>
82629e3015252bf18319ba3815c773df23e21436Mike Christensen<div class="refsect1" lang="en">
82629e3015252bf18319ba3815c773df23e21436Mike Christensen<a name="id2543437"></a><h2>DESCRIPTION</h2>
82629e3015252bf18319ba3815c773df23e21436Mike Christensen<p><span><strong class="command">host</strong></span>
82629e3015252bf18319ba3815c773df23e21436Mike Christensen      is a simple utility for performing DNS lookups.
82629e3015252bf18319ba3815c773df23e21436Mike Christensen      It is normally used to convert names to IP addresses and vice versa.
82629e3015252bf18319ba3815c773df23e21436Mike Christensen      When no arguments or options are given,
82629e3015252bf18319ba3815c773df23e21436Mike Christensen      <span><strong class="command">host</strong></span>
82629e3015252bf18319ba3815c773df23e21436Mike Christensen      prints a short summary of its command line arguments and options.
82629e3015252bf18319ba3815c773df23e21436Mike Christensen    </p>
82629e3015252bf18319ba3815c773df23e21436Mike Christensen<p><em class="parameter"><code>name</code></em> is the domain name that is to be
82629e3015252bf18319ba3815c773df23e21436Mike Christensen      looked
82629e3015252bf18319ba3815c773df23e21436Mike Christensen      up.  It can also be a dotted-decimal IPv4 address or a colon-delimited
82629e3015252bf18319ba3815c773df23e21436Mike Christensen      IPv6 address, in which case <span><strong class="command">host</strong></span> will by
82629e3015252bf18319ba3815c773df23e21436Mike Christensen      default
82629e3015252bf18319ba3815c773df23e21436Mike Christensen      perform a reverse lookup for that address.
82629e3015252bf18319ba3815c773df23e21436Mike Christensen      <em class="parameter"><code>server</code></em> is an optional argument which
82629e3015252bf18319ba3815c773df23e21436Mike Christensen      is either
82629e3015252bf18319ba3815c773df23e21436Mike Christensen      the name or IP address of the name server that <span><strong class="command">host</strong></span>
82629e3015252bf18319ba3815c773df23e21436Mike Christensen      should query instead of the server or servers listed in
82629e3015252bf18319ba3815c773df23e21436Mike Christensen      <code class="filename">/etc/resolv.conf</code>.
    </p>
<p>
      The <code class="option">-a</code> (all) option is equivalent to setting the
      <code class="option">-v</code> option and asking <span><strong class="command">host</strong></span> to make
      a query of type ANY.
    </p>
<p>
      When the <code class="option">-C</code> option is used, <span><strong class="command">host</strong></span>
      will attempt to display the SOA records for zone
      <em class="parameter"><code>name</code></em> from all the listed
      authoritative name
      servers for that zone.  The list of name servers is defined by the NS
      records that are found for the zone.
    </p>
<p>
      The <code class="option">-c</code> option instructs to make a DNS query of class
      <em class="parameter"><code>class</code></em>.  This can be used to lookup
      Hesiod or
      Chaosnet class resource records.  The default class is IN (Internet).
    </p>
<p>
      Verbose output is generated by <span><strong class="command">host</strong></span> when
      the
      <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, AAAA, and MX 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="id2543803"></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="id2543826"></a><h2>FILES</h2>
<p><code class="filename">/etc/resolv.conf</code>
    </p>
</div>
<div class="refsect1" lang="en">
<a name="id2543837"></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>
</div>
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