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  43 <a name="man.host"></a><div class="titlepage"></div>
  44 <div class="refnamediv">
  45 <h2>Name</h2>
  46 <p>host &#8212; DNS lookup utility</p>
  47 </div>
  48 <div class="refsynopsisdiv">
  49 <h2>Synopsis</h2>
  50 <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>
  51 </div>
  52 <div class="refsect1" lang="en">
  53 <a name="id2614302"></a><h2>DESCRIPTION</h2>
  54 <p><span><strong class="command">host</strong></span>
  55       is a simple utility for performing DNS lookups.
  56       It is normally used to convert names to IP addresses and vice versa.
  57       When no arguments or options are given,
  58       <span><strong class="command">host</strong></span>
  59       prints a short summary of its command line arguments and options.
  60     </p>
  61 <p><em class="parameter"><code>name</code></em> is the domain name that is to be
  62       looked
  63       up.  It can also be a dotted-decimal IPv4 address or a colon-delimited
  64       IPv6 address, in which case <span><strong class="command">host</strong></span> will by
  65       default
  66       perform a reverse lookup for that address.
  67       <em class="parameter"><code>server</code></em> is an optional argument which
  68       is either
  69       the name or IP address of the name server that <span><strong class="command">host</strong></span>
  70       should query instead of the server or servers listed in
  71       <code class="filename">/etc/resolv.conf</code>.
  72     </p>
  73 <p>
  74       The <code class="option">-a</code> (all) option is equivalent to setting the
  75       <code class="option">-v</code> option and asking <span><strong class="command">host</strong></span> to make
  76       a query of type ANY.
  77     </p>
  78 <p>
  79       When the <code class="option">-C</code> option is used, <span><strong class="command">host</strong></span>
  80       will attempt to display the SOA records for zone
  81       <em class="parameter"><code>name</code></em> from all the listed
  82       authoritative name
  83       servers for that zone.  The list of name servers is defined by the NS
  84       records that are found for the zone.
  85     </p>
  86 <p>
  87       The <code class="option">-c</code> option instructs to make a DNS query of class
  88       <em class="parameter"><code>class</code></em>.  This can be used to lookup
  89       Hesiod or
  90       Chaosnet class resource records.  The default class is IN (Internet).
  91     </p>
  92 <p>
  93       Verbose output is generated by <span><strong class="command">host</strong></span> when
  94       the
  95       <code class="option">-d</code> or <code class="option">-v</code> option is used.  The two
  96       options are equivalent.  They have been provided for backwards
  97       compatibility.  In previous versions, the <code class="option">-d</code> option
  98       switched on debugging traces and <code class="option">-v</code> enabled verbose
  99       output.
 100     </p>
 101 <p>
 102       List mode is selected by the <code class="option">-l</code> option.  This makes
 103       <span><strong class="command">host</strong></span> perform a zone transfer for zone
 104       <em class="parameter"><code>name</code></em>.  Transfer the zone printing out
 105       the NS, PTR
 106       and address records (A/AAAA).  If combined with <code class="option">-a</code>
 107       all records will be printed.
 108     </p>
 109 <p>
 110       The <code class="option">-i</code>
 111       option specifies that reverse lookups of IPv6 addresses should
 112       use the IP6.INT domain as defined in RFC1886.
 113       The default is to use IP6.ARPA.
 114     </p>
 115 <p>
 116       The <code class="option">-N</code> option sets the number of dots that have to be
 117       in <em class="parameter"><code>name</code></em> for it to be considered
 118       absolute.  The
 119       default value is that defined using the ndots statement in
 120       <code class="filename">/etc/resolv.conf</code>, or 1 if no ndots
 121       statement is
 122       present.  Names with fewer dots are interpreted as relative names and
 123       will be searched for in the domains listed in the <span class="type">search</span>
 124       or <span class="type">domain</span> directive in
 125       <code class="filename">/etc/resolv.conf</code>.
 126     </p>
 127 <p>
 128       The number of UDP retries for a lookup can be changed with the
 129       <code class="option">-R</code> option.  <em class="parameter"><code>number</code></em>
 130       indicates
 131       how many times <span><strong class="command">host</strong></span> will repeat a query
 132       that does
 133       not get answered.  The default number of retries is 1.  If
 134       <em class="parameter"><code>number</code></em> is negative or zero, the
 135       number of
 136       retries will default to 1.
 137     </p>
 138 <p>
 139       Non-recursive queries can be made via the <code class="option">-r</code> option.
 140       Setting this option clears the <span class="type">RD</span> &#8212; recursion
 141       desired &#8212; bit in the query which <span><strong class="command">host</strong></span> makes.
 142       This should mean that the name server receiving the query will not
 143       attempt to resolve <em class="parameter"><code>name</code></em>.  The
 144       <code class="option">-r</code> option enables <span><strong class="command">host</strong></span>
 145       to mimic
 146       the behavior of a name server by making non-recursive queries and
 147       expecting to receive answers to those queries that are usually
 148       referrals to other name servers.
 149     </p>
 150 <p>
 151       By default, <span><strong class="command">host</strong></span> uses UDP when making
 152       queries.  The
 153       <code class="option">-T</code> option makes it use a TCP connection when querying
 154       the name server.  TCP will be automatically selected for queries that
 155       require it, such as zone transfer (AXFR) requests.
 156     </p>
 157 <p>
 158       The <code class="option">-4</code> option forces <span><strong class="command">host</strong></span> to only
 159       use IPv4 query transport.  The <code class="option">-6</code> option forces
 160       <span><strong class="command">host</strong></span> to only use IPv6 query transport.
 161     </p>
 162 <p>
 163       The <code class="option">-t</code> option is used to select the query type.
 164       <em class="parameter"><code>type</code></em> can be any recognized query
 165       type: CNAME,
 166       NS, SOA, SIG, KEY, AXFR, etc.  When no query type is specified,
 167       <span><strong class="command">host</strong></span> automatically selects an appropriate
 168       query
 169       type.  By default, it looks for A, AAAA, and MX records, but if the
 170       <code class="option">-C</code> option was given, queries will be made for SOA
 171       records, and if <em class="parameter"><code>name</code></em> is a
 172       dotted-decimal IPv4
 173       address or colon-delimited IPv6 address, <span><strong class="command">host</strong></span> will
 174       query for PTR records.  If a query type of IXFR is chosen the starting
 175       serial number can be specified by appending an equal followed by the
 176       starting serial number (e.g. -t IXFR=12345678).
 177     </p>
 178 <p>
 179       The time to wait for a reply can be controlled through the
 180       <code class="option">-W</code> and <code class="option">-w</code> options.  The
 181       <code class="option">-W</code> option makes <span><strong class="command">host</strong></span>
 182       wait for
 183       <em class="parameter"><code>wait</code></em> seconds.  If <em class="parameter"><code>wait</code></em>
 184       is less than one, the wait interval is set to one second.  When the
 185       <code class="option">-w</code> option is used, <span><strong class="command">host</strong></span>
 186       will
 187       effectively wait forever for a reply.  The time to wait for a response
 188       will be set to the number of seconds given by the hardware's maximum
 189       value for an integer quantity.
 190     </p>
 191 <p>
 192       The <code class="option">-s</code> option tells <span><strong class="command">host</strong></span>
 193       <span class="emphasis"><em>not</em></span> to send the query to the next nameserver
 194       if any server responds with a SERVFAIL response, which is the
 195       reverse of normal stub resolver behavior.
 196     </p>
 197 <p>
 198       The <code class="option">-m</code> can be used to set the memory usage debugging
 199       flags
 200       <em class="parameter"><code>record</code></em>, <em class="parameter"><code>usage</code></em> and
 201       <em class="parameter"><code>trace</code></em>.
 202     </p>
 203 <p>
 204       The <code class="option">-V</code> option causes <span><strong class="command">host</strong></span>
 205       to print the version number and exit.
 206     </p>
 207 </div>
 208 <div class="refsect1" lang="en">
 209 <a name="id2614966"></a><h2>IDN SUPPORT</h2>
 210 <p>
 211       If <span><strong class="command">host</strong></span> has been built with IDN (internationalized
 212       domain name) support, it can accept and display non-ASCII domain names.
 213       <span><strong class="command">host</strong></span> appropriately converts character encoding of
 214       domain name before sending a request to DNS server or displaying a
 215       reply from the server.
 216       If you'd like to turn off the IDN support for some reason, defines
 217       the <code class="envar">IDN_DISABLE</code> environment variable.
 218       The IDN support is disabled if the variable is set when
 219       <span><strong class="command">host</strong></span> runs.
 220     </p>
 221 </div>
 222 <div class="refsect1" lang="en">
 223 <a name="id2614995"></a><h2>FILES</h2>
 224 <p><code class="filename">/etc/resolv.conf</code>
 225     </p>
 226 </div>
 227 <div class="refsect1" lang="en">
 228 <a name="id2615009"></a><h2>SEE ALSO</h2>
 229 <p><span class="citerefentry"><span class="refentrytitle">dig</span>(1)</span>,
 230       <span class="citerefentry"><span class="refentrytitle">named</span>(8)</span>.
 231     </p>
 232 </div>
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