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4bff34e37def8a90f9194d81bc345c52ba20086athurlow<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>
4bff34e37def8a90f9194d81bc345c52ba20086athurlow<p><span><strong class="command">host</strong></span>
4bff34e37def8a90f9194d81bc345c52ba20086athurlow is a simple utility for performing DNS lookups.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow It is normally used to convert names to IP addresses and vice versa.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow When no arguments or options are given,
613a2f6ba31e891e3d947a356daf5e563d43c1ceGordon Ross prints a short summary of its command line arguments and options.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow<p><em class="parameter"><code>name</code></em> is the domain name that is to be
4bff34e37def8a90f9194d81bc345c52ba20086athurlow up. It can also be a dotted-decimal IPv4 address or a colon-delimited
4bff34e37def8a90f9194d81bc345c52ba20086athurlow IPv6 address, in which case <span><strong class="command">host</strong></span> will by
4bff34e37def8a90f9194d81bc345c52ba20086athurlow perform a reverse lookup for that address.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <em class="parameter"><code>server</code></em> is an optional argument which
4bff34e37def8a90f9194d81bc345c52ba20086athurlow the name or IP address of the name server that <span><strong class="command">host</strong></span>
4bff34e37def8a90f9194d81bc345c52ba20086athurlow should query instead of the server or servers listed in
4bff34e37def8a90f9194d81bc345c52ba20086athurlow The <code class="option">-a</code> (all) option is equivalent to setting the
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <code class="option">-v</code> option and asking <span><strong class="command">host</strong></span> to make
4bff34e37def8a90f9194d81bc345c52ba20086athurlow a query of type ANY.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow When the <code class="option">-C</code> option is used, <span><strong class="command">host</strong></span>
4bff34e37def8a90f9194d81bc345c52ba20086athurlow will attempt to display the SOA records for zone
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <em class="parameter"><code>name</code></em> from all the listed
4bff34e37def8a90f9194d81bc345c52ba20086athurlow authoritative name
4bff34e37def8a90f9194d81bc345c52ba20086athurlow servers for that zone. The list of name servers is defined by the NS
4bff34e37def8a90f9194d81bc345c52ba20086athurlow records that are found for the zone.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow The <code class="option">-c</code> option instructs to make a DNS query of class
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <em class="parameter"><code>class</code></em>. This can be used to lookup
4bff34e37def8a90f9194d81bc345c52ba20086athurlow Chaosnet class resource records. The default class is IN (Internet).
4bff34e37def8a90f9194d81bc345c52ba20086athurlow Verbose output is generated by <span><strong class="command">host</strong></span> when
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <code class="option">-d</code> or <code class="option">-v</code> option is used. The two
4bff34e37def8a90f9194d81bc345c52ba20086athurlow options are equivalent. They have been provided for backwards
4bff34e37def8a90f9194d81bc345c52ba20086athurlow compatibility. In previous versions, the <code class="option">-d</code> option
4bff34e37def8a90f9194d81bc345c52ba20086athurlow switched on debugging traces and <code class="option">-v</code> enabled verbose
4bff34e37def8a90f9194d81bc345c52ba20086athurlow List mode is selected by the <code class="option">-l</code> option. This makes
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <span><strong class="command">host</strong></span> perform a zone transfer for zone
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <em class="parameter"><code>name</code></em>. Transfer the zone printing out
4bff34e37def8a90f9194d81bc345c52ba20086athurlow the NS, PTR
4bff34e37def8a90f9194d81bc345c52ba20086athurlow and address records (A/AAAA). If combined with <code class="option">-a</code>
4bff34e37def8a90f9194d81bc345c52ba20086athurlow all records will be printed.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow option specifies that reverse lookups of IPv6 addresses should
4bff34e37def8a90f9194d81bc345c52ba20086athurlow use the IP6.INT domain as defined in RFC1886.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow The default is to use IP6.ARPA.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow The <code class="option">-N</code> option sets the number of dots that have to be
4bff34e37def8a90f9194d81bc345c52ba20086athurlow in <em class="parameter"><code>name</code></em> for it to be considered
4bff34e37def8a90f9194d81bc345c52ba20086athurlow absolute. The
4bff34e37def8a90f9194d81bc345c52ba20086athurlow default value is that defined using the ndots statement in
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <code class="filename">/etc/resolv.conf</code>, or 1 if no ndots
4bff34e37def8a90f9194d81bc345c52ba20086athurlow statement is
4bff34e37def8a90f9194d81bc345c52ba20086athurlow present. Names with fewer dots are interpreted as relative names and
4bff34e37def8a90f9194d81bc345c52ba20086athurlow will be searched for in the domains listed in the <span class="type">search</span>
4bff34e37def8a90f9194d81bc345c52ba20086athurlow The number of UDP retries for a lookup can be changed with the
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <code class="option">-R</code> option. <em class="parameter"><code>number</code></em>
4bff34e37def8a90f9194d81bc345c52ba20086athurlow how many times <span><strong class="command">host</strong></span> will repeat a query
4bff34e37def8a90f9194d81bc345c52ba20086athurlow not get answered. The default number of retries is 1. If
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <em class="parameter"><code>number</code></em> is negative or zero, the
4bff34e37def8a90f9194d81bc345c52ba20086athurlow retries will default to 1.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow Non-recursive queries can be made via the <code class="option">-r</code> option.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow Setting this option clears the <span class="type">RD</span> — recursion
4bff34e37def8a90f9194d81bc345c52ba20086athurlow desired — bit in the query which <span><strong class="command">host</strong></span> makes.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow This should mean that the name server receiving the query will not
4bff34e37def8a90f9194d81bc345c52ba20086athurlow attempt to resolve <em class="parameter"><code>name</code></em>. The
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <code class="option">-r</code> option enables <span><strong class="command">host</strong></span>
4bff34e37def8a90f9194d81bc345c52ba20086athurlow the behavior of a name server by making non-recursive queries and
4bff34e37def8a90f9194d81bc345c52ba20086athurlow expecting to receive answers to those queries that are usually
4bff34e37def8a90f9194d81bc345c52ba20086athurlow referrals to other name servers.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow By default, <span><strong class="command">host</strong></span> uses UDP when making
4bff34e37def8a90f9194d81bc345c52ba20086athurlow queries. The
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <code class="option">-T</code> option makes it use a TCP connection when querying
4bff34e37def8a90f9194d81bc345c52ba20086athurlow the name server. TCP will be automatically selected for queries that
4bff34e37def8a90f9194d81bc345c52ba20086athurlow require it, such as zone transfer (AXFR) requests.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow The <code class="option">-4</code> option forces <span><strong class="command">host</strong></span> to only
4bff34e37def8a90f9194d81bc345c52ba20086athurlow use IPv4 query transport. The <code class="option">-6</code> option forces
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <span><strong class="command">host</strong></span> to only use IPv6 query transport.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow The <code class="option">-t</code> option is used to select the query type.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <em class="parameter"><code>type</code></em> can be any recognized query
4bff34e37def8a90f9194d81bc345c52ba20086athurlow type: CNAME,
4bff34e37def8a90f9194d81bc345c52ba20086athurlow NS, SOA, SIG, KEY, AXFR, etc. When no query type is specified,
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <span><strong class="command">host</strong></span> automatically selects an appropriate
4bff34e37def8a90f9194d81bc345c52ba20086athurlow type. By default, it looks for A, AAAA, and MX records, but if the
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <code class="option">-C</code> option was given, queries will be made for SOA
4bff34e37def8a90f9194d81bc345c52ba20086athurlow records, and if <em class="parameter"><code>name</code></em> is a
4bff34e37def8a90f9194d81bc345c52ba20086athurlow dotted-decimal IPv4
4bff34e37def8a90f9194d81bc345c52ba20086athurlow address or colon-delimited IPv6 address, <span><strong class="command">host</strong></span> will
4bff34e37def8a90f9194d81bc345c52ba20086athurlow query for PTR records. If a query type of IXFR is chosen the starting
4bff34e37def8a90f9194d81bc345c52ba20086athurlow serial number can be specified by appending an equal followed by the
4bff34e37def8a90f9194d81bc345c52ba20086athurlow starting serial number (e.g. -t IXFR=12345678).
4bff34e37def8a90f9194d81bc345c52ba20086athurlow The time to wait for a reply can be controlled through the
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <code class="option">-W</code> and <code class="option">-w</code> options. The
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <code class="option">-W</code> option makes <span><strong class="command">host</strong></span>
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <em class="parameter"><code>wait</code></em> seconds. If <em class="parameter"><code>wait</code></em>
4bff34e37def8a90f9194d81bc345c52ba20086athurlow is less than one, the wait interval is set to one second. When the
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <code class="option">-w</code> option is used, <span><strong class="command">host</strong></span>
4bff34e37def8a90f9194d81bc345c52ba20086athurlow effectively wait forever for a reply. The time to wait for a response
4bff34e37def8a90f9194d81bc345c52ba20086athurlow will be set to the number of seconds given by the hardware's maximum
4bff34e37def8a90f9194d81bc345c52ba20086athurlow value for an integer quantity.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow The <code class="option">-s</code> option tells <span><strong class="command">host</strong></span>
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <span class="emphasis"><em>not</em></span> to send the query to the next nameserver
4bff34e37def8a90f9194d81bc345c52ba20086athurlow if any server responds with a SERVFAIL response, which is the
4bff34e37def8a90f9194d81bc345c52ba20086athurlow reverse of normal stub resolver behavior.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow The <code class="option">-m</code> can be used to set the memory usage debugging
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <em class="parameter"><code>record</code></em>, <em class="parameter"><code>usage</code></em> and
4bff34e37def8a90f9194d81bc345c52ba20086athurlow If <span><strong class="command">host</strong></span> has been built with IDN (internationalized
4bff34e37def8a90f9194d81bc345c52ba20086athurlow domain name) support, it can accept and display non-ASCII domain names.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <span><strong class="command">host</strong></span> appropriately converts character encoding of
4bff34e37def8a90f9194d81bc345c52ba20086athurlow domain name before sending a request to DNS server or displaying a
4bff34e37def8a90f9194d81bc345c52ba20086athurlow reply from the server.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow If you'd like to turn off the IDN support for some reason, defines
4bff34e37def8a90f9194d81bc345c52ba20086athurlow the <code class="envar">IDN_DISABLE</code> environment variable.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow The IDN support is disabled if the variable is set when
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <span><strong class="command">host</strong></span> runs.
4bff34e37def8a90f9194d81bc345c52ba20086athurlow<p><span class="citerefentry"><span class="refentrytitle">dig</span>(1)</span>,
4bff34e37def8a90f9194d81bc345c52ba20086athurlow <span class="citerefentry"><span class="refentrytitle">named</span>(8)</span>.
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