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7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User — DNS lookup utility
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User [<code class="option">-c <em class="replaceable"><code>class</code></em></code>]
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User [<code class="option">-N <em class="replaceable"><code>ndots</code></em></code>]
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User [<code class="option">-R <em class="replaceable"><code>number</code></em></code>]
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User [<code class="option">-t <em class="replaceable"><code>type</code></em></code>]
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User [<code class="option">-W <em class="replaceable"><code>wait</code></em></code>]
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User [<code class="option">-m <em class="replaceable"><code>flag</code></em></code>]
1e9517ea2156b990be21f44676d3370318eacf17Tinderbox User<a name="id-1.14.4.7"></a><h2>DESCRIPTION</h2>
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User <p><span class="command"><strong>host</strong></span>
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews is a simple utility for performing DNS lookups.
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews It is normally used to convert names to IP addresses and vice versa.
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews When no arguments or options are given,
14a656f94b1fd0ababd84a772228dfa52276ba15Evan Hunt <span class="command"><strong>host</strong></span>
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews prints a short summary of its command line arguments and options.
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User <p><em class="parameter"><code>name</code></em> is the domain name that is to be
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews up. It can also be a dotted-decimal IPv4 address or a colon-delimited
14a656f94b1fd0ababd84a772228dfa52276ba15Evan Hunt IPv6 address, in which case <span class="command"><strong>host</strong></span> will by
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews perform a reverse lookup for that address.
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews <em class="parameter"><code>server</code></em> is an optional argument which
14a656f94b1fd0ababd84a772228dfa52276ba15Evan Hunt the name or IP address of the name server that <span class="command"><strong>host</strong></span>
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews should query instead of the server or servers listed in
5a4557e8de2951a2796676b5ec4b6a90caa5be14Mark Andrews <code class="filename">/etc/resolv.conf</code>.
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User <div class="variablelist"><dl class="variablelist">
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User Use IPv4 only for query transport.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User See also the <code class="option">-6</code> option.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User Use IPv6 only for query transport.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User See also the <code class="option">-4</code> option.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User "All". The <code class="option">-a</code> option is normally equivalent
260e8e04b0dc24cb884c789b5d9eb046457f264eTinderbox User to <code class="option">-v -t <code class="literal">ANY</code></code>.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User It also affects the behaviour of the <code class="option">-l</code>
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User list zone option.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User<dt><span class="term">-c <em class="replaceable"><code>class</code></em></span></dt>
260e8e04b0dc24cb884c789b5d9eb046457f264eTinderbox User Query class: This can be used to lookup HS (Hesiod) or CH
260e8e04b0dc24cb884c789b5d9eb046457f264eTinderbox User (Chaosnet) class resource records. The default class is IN
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User Check consistency: <span class="command"><strong>host</strong></span> will query the
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User SOA records for zone <em class="parameter"><code>name</code></em> from all
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User the listed authoritative name servers for that zone. The
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User list of name servers is defined by the NS records that are
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User found for the zone.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User Print debugging traces.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User Equivalent to the <code class="option">-v</code> verbose option.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User Use the IP6.INT domain for reverse lookups of IPv6
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User addresses as defined in RFC1886 and deprecated in RFC4159.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User The default is to use IP6.ARPA as specified in RFC3596.
260e8e04b0dc24cb884c789b5d9eb046457f264eTinderbox User The <span class="command"><strong>host</strong></span> command performs a zone transfer of
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User zone <em class="parameter"><code>name</code></em> and prints out the NS,
260e8e04b0dc24cb884c789b5d9eb046457f264eTinderbox User Together, the <code class="option">-l -a</code>
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User options print all records in the zone.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User<dt><span class="term">-N <em class="replaceable"><code>ndots</code></em></span></dt>
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User The number of dots that have to be
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User in <em class="parameter"><code>name</code></em> for it to be considered
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User absolute. The default value is that defined using the
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User ndots statement in <code class="filename">/etc/resolv.conf</code>,
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User or 1 if no ndots statement is present. Names with fewer
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User dots are interpreted as relative names and will be
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User searched for in the domains listed in
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User the <span class="type">search</span> or <span class="type">domain</span> directive
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User in <code class="filename">/etc/resolv.conf</code>.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User Non-recursive query:
260e8e04b0dc24cb884c789b5d9eb046457f264eTinderbox User Setting this option clears the RD (recursion desired) bit
260e8e04b0dc24cb884c789b5d9eb046457f264eTinderbox User in the query. This should mean that the name server
260e8e04b0dc24cb884c789b5d9eb046457f264eTinderbox User receiving the query will not attempt to
260e8e04b0dc24cb884c789b5d9eb046457f264eTinderbox User resolve <em class="parameter"><code>name</code></em>.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User enables <span class="command"><strong>host</strong></span> to mimic the behavior of a
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User name server by making non-recursive queries and expecting
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User to receive answers to those queries that can be
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User referrals to other name servers.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User<dt><span class="term">-R <em class="replaceable"><code>number</code></em></span></dt>
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User Number of retries for UDP queries:
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User If <em class="parameter"><code>number</code></em> is negative or zero, the
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User number of retries will default to 1. The default value is
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User 1, or the value of the <em class="parameter"><code>attempts</code></em>
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User option in <code class="filename">/etc/resolv.conf</code>, if set.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User Do <span class="emphasis"><em>not</em></span> send the query to the next
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User nameserver if any server responds with a SERVFAIL
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User response, which is the reverse of normal stub resolver
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User<dt><span class="term">-t <em class="replaceable"><code>type</code></em></span></dt>
260e8e04b0dc24cb884c789b5d9eb046457f264eTinderbox User The <em class="parameter"><code>type</code></em> argument can be any
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User recognized query type: CNAME, NS, SOA, TXT, DNSKEY, AXFR, etc.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User When no query type is specified, <span class="command"><strong>host</strong></span>
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User automatically selects an appropriate query type. By default, it
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User looks for A, AAAA, and MX records.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User If the <code class="option">-C</code> option is given, queries will
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User be made for SOA records.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User If <em class="parameter"><code>name</code></em> is a dotted-decimal IPv4
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User address or colon-delimited IPv6
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User address, <span class="command"><strong>host</strong></span> will query for PTR
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User If a query type of IXFR is chosen the starting serial
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User number can be specified by appending an equal followed by
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User the starting serial number
260e8e04b0dc24cb884c789b5d9eb046457f264eTinderbox User (like <code class="option">-t <code class="literal">IXFR=12345678</code></code>).
c32570b3191fdfb38a65567b8bb729fdb42ff847Tinderbox User<span class="term">-T, </span><span class="term">-U</span>
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User By default, <span class="command"><strong>host</strong></span> uses UDP when making
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User queries. The <code class="option">-T</code> option makes it use a TCP
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User connection when querying the name server. TCP will be
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User automatically selected for queries that require it, such
c32570b3191fdfb38a65567b8bb729fdb42ff847Tinderbox User as zone transfer (AXFR) requests. Type ANY queries default
c32570b3191fdfb38a65567b8bb729fdb42ff847Tinderbox User to TCP but can be forced to UDP initially using <code class="option">-U</code>.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User<dt><span class="term">-m <em class="replaceable"><code>flag</code></em></span></dt>
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User Memory usage debugging: the flag can
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User be <em class="parameter"><code>record</code></em>, <em class="parameter"><code>usage</code></em>,
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User or <em class="parameter"><code>trace</code></em>. You can specify
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User the <code class="option">-m</code> option more than once to set
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User multiple flags.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User Verbose output.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User Equivalent to the <code class="option">-d</code> debug option.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User Verbose output can also be enabled by setting
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User the <em class="parameter"><code>debug</code></em> option
260e8e04b0dc24cb884c789b5d9eb046457f264eTinderbox User in <code class="filename">/etc/resolv.conf</code>.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User Print the version number and exit.
260e8e04b0dc24cb884c789b5d9eb046457f264eTinderbox User Wait forever: The query timeout is set to the maximum possible.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User See also the <code class="option">-W</code> option.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User<dt><span class="term">-W <em class="replaceable"><code>wait</code></em></span></dt>
260e8e04b0dc24cb884c789b5d9eb046457f264eTinderbox User Timeout: Wait for up to <em class="parameter"><code>wait</code></em>
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User seconds for a reply. If <em class="parameter"><code>wait</code></em> is
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User less than one, the wait interval is set to one second.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User By default, <span class="command"><strong>host</strong></span> will wait for 5
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User seconds for UDP responses and 10 seconds for TCP
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User connections. These defaults can be overridden by
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User the <em class="parameter"><code>timeout</code></em> option
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User in <code class="filename">/etc/resolv.conf</code>.
3241ddcf9354c5ab50f4df5a656e72a5c68e172bTinderbox User See also the <code class="option">-w</code> option.
1e9517ea2156b990be21f44676d3370318eacf17Tinderbox User<a name="id-1.14.4.9"></a><h2>IDN SUPPORT</h2>
14a656f94b1fd0ababd84a772228dfa52276ba15Evan Hunt If <span class="command"><strong>host</strong></span> has been built with IDN (internationalized
9d557856c2a19ec95ee73245f60a92f8675cf5baTinderbox User domain name) support, it can accept and display non-ASCII domain names.
14a656f94b1fd0ababd84a772228dfa52276ba15Evan Hunt <span class="command"><strong>host</strong></span> appropriately converts character encoding of
057cafaa3df7be7a6dcca71fbaf8fb498fd83518Mark Andrews domain name before sending a request to DNS server or displaying a
057cafaa3df7be7a6dcca71fbaf8fb498fd83518Mark Andrews reply from the server.
057cafaa3df7be7a6dcca71fbaf8fb498fd83518Mark Andrews If you'd like to turn off the IDN support for some reason, defines
057cafaa3df7be7a6dcca71fbaf8fb498fd83518Mark Andrews the <code class="envar">IDN_DISABLE</code> environment variable.
057cafaa3df7be7a6dcca71fbaf8fb498fd83518Mark Andrews The IDN support is disabled if the variable is set when
14a656f94b1fd0ababd84a772228dfa52276ba15Evan Hunt <span class="command"><strong>host</strong></span> runs.
7911e6f9de303bca5a3d8b34f4330c8f7cecffaeTinderbox User <p><code class="filename">/etc/resolv.conf</code>
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350e5eecadfc5ee72b11b2cc46828c9a0bcd717cTinderbox User<p xmlns:db="http://docbook.org/ns/docbook" style="text-align: center;">BIND 9.11.2 (Extended Support Version)</p>