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b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync — DNS lookup utility
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync [<code class="option">-c <em class="replaceable"><code>class</code></em></code>]
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync [<code class="option">-N <em class="replaceable"><code>ndots</code></em></code>]
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync [<code class="option">-R <em class="replaceable"><code>number</code></em></code>]
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync [<code class="option">-t <em class="replaceable"><code>type</code></em></code>]
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync [<code class="option">-W <em class="replaceable"><code>wait</code></em></code>]
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync [<code class="option">-m <em class="replaceable"><code>flag</code></em></code>]
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync <p><span class="command"><strong>host</strong></span>
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync is a simple utility for performing DNS lookups.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync It is normally used to convert names to IP addresses and vice versa.
d1966fe9681e9a100f8c895f08e450fc32dafd48vboxsync When no arguments or options are given,
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync prints a short summary of its command line arguments and options.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync <p><em class="parameter"><code>name</code></em> is the domain name that is to be
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync up. It can also be a dotted-decimal IPv4 address or a colon-delimited
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync IPv6 address, in which case <span class="command"><strong>host</strong></span> will by
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync perform a reverse lookup for that address.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync <em class="parameter"><code>server</code></em> is an optional argument which
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync the name or IP address of the name server that <span class="command"><strong>host</strong></span>
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync should query instead of the server or servers listed in
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync <div class="variablelist"><dl class="variablelist">
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Use IPv4 only for query transport.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync See also the <code class="option">-6</code> option.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Use IPv6 only for query transport.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync See also the <code class="option">-4</code> option.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync "All". The <code class="option">-a</code> option is normally equivalent
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync to <code class="option">-v -t <code class="literal">ANY</code></code>.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync It also affects the behaviour of the <code class="option">-l</code>
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync list zone option.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync<dt><span class="term">-c <em class="replaceable"><code>class</code></em></span></dt>
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Query class: This can be used to lookup HS (Hesiod) or CH
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync (Chaosnet) class resource records. The default class is IN
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync (Internet).
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Check consistency: <span class="command"><strong>host</strong></span> will query the
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync SOA records for zone <em class="parameter"><code>name</code></em> from all
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync the listed authoritative name servers for that zone. The
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync list of name servers is defined by the NS records that are
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync found for the zone.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Print debugging traces.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Equivalent to the <code class="option">-v</code> verbose option.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Use the IP6.INT domain for reverse lookups of IPv6
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync addresses as defined in RFC1886 and deprecated in RFC4159.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync The default is to use IP6.ARPA as specified in RFC3596.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync The <span class="command"><strong>host</strong></span> command performs a zone transfer of
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync zone <em class="parameter"><code>name</code></em> and prints out the NS,
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync options print all records in the zone.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync<dt><span class="term">-N <em class="replaceable"><code>ndots</code></em></span></dt>
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync The number of dots that have to be
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync in <em class="parameter"><code>name</code></em> for it to be considered
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync absolute. The default value is that defined using the
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync ndots statement in <code class="filename">/etc/resolv.conf</code>,
7d0cc752907fa7423e9d6558ecea067a10f0dd77vboxsync or 1 if no ndots statement is present. Names with fewer
7d0cc752907fa7423e9d6558ecea067a10f0dd77vboxsync dots are interpreted as relative names and will be
7d0cc752907fa7423e9d6558ecea067a10f0dd77vboxsync searched for in the domains listed in
7d0cc752907fa7423e9d6558ecea067a10f0dd77vboxsync the <span class="type">search</span> or <span class="type">domain</span> directive
7d0cc752907fa7423e9d6558ecea067a10f0dd77vboxsync Non-recursive query:
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Setting this option clears the RD (recursion desired) bit
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync in the query. This should mean that the name server
d1966fe9681e9a100f8c895f08e450fc32dafd48vboxsync receiving the query will not attempt to
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync resolve <em class="parameter"><code>name</code></em>.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync enables <span class="command"><strong>host</strong></span> to mimic the behavior of a
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync name server by making non-recursive queries and expecting
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync to receive answers to those queries that can be
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync referrals to other name servers.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync<dt><span class="term">-R <em class="replaceable"><code>number</code></em></span></dt>
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Number of retries for UDP queries:
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync If <em class="parameter"><code>number</code></em> is negative or zero, the
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync number of retries will default to 1. The default value is
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync 1, or the value of the <em class="parameter"><code>attempts</code></em>
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync option in <code class="filename">/etc/resolv.conf</code>, if set.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Do <span class="emphasis"><em>not</em></span> send the query to the next
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync nameserver if any server responds with a SERVFAIL
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync response, which is the reverse of normal stub resolver
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync<dt><span class="term">-t <em class="replaceable"><code>type</code></em></span></dt>
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Query type:
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync The <em class="parameter"><code>type</code></em> argument can be any
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync recognized query type: CNAME, NS, SOA, TXT, DNSKEY, AXFR, etc.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync When no query type is specified, <span class="command"><strong>host</strong></span>
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync automatically selects an appropriate query type. By default, it
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync looks for A, AAAA, and MX records.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync If the <code class="option">-C</code> option is given, queries will
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync be made for SOA records.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync If <em class="parameter"><code>name</code></em> is a dotted-decimal IPv4
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync address or colon-delimited IPv6
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync address, <span class="command"><strong>host</strong></span> will query for PTR
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync If a query type of IXFR is chosen the starting serial
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync number can be specified by appending an equal followed by
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync the starting serial number
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync (like <code class="option">-t <code class="literal">IXFR=12345678</code></code>).
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync<span class="term">-T, </span><span class="term">-U</span>
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync By default, <span class="command"><strong>host</strong></span> uses UDP when making
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync queries. The <code class="option">-T</code> option makes it use a TCP
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync connection when querying the name server. TCP will be
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync automatically selected for queries that require it, such
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync as zone transfer (AXFR) requests. Type ANY queries default
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync to TCP but can be forced to UDP initially using <code class="option">-U</code>.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync<dt><span class="term">-m <em class="replaceable"><code>flag</code></em></span></dt>
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Memory usage debugging: the flag can
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync be <em class="parameter"><code>record</code></em>, <em class="parameter"><code>usage</code></em>,
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync or <em class="parameter"><code>trace</code></em>. You can specify
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync the <code class="option">-m</code> option more than once to set
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync multiple flags.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Verbose output.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Equivalent to the <code class="option">-d</code> debug option.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Verbose output can also be enabled by setting
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync the <em class="parameter"><code>debug</code></em> option
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Print the version number and exit.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Wait forever: The query timeout is set to the maximum possible.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync See also the <code class="option">-W</code> option.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync<dt><span class="term">-W <em class="replaceable"><code>wait</code></em></span></dt>
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync Timeout: Wait for up to <em class="parameter"><code>wait</code></em>
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync seconds for a reply. If <em class="parameter"><code>wait</code></em> is
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync less than one, the wait interval is set to one second.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync By default, <span class="command"><strong>host</strong></span> will wait for 5
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync seconds for UDP responses and 10 seconds for TCP
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync connections. These defaults can be overridden by
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync the <em class="parameter"><code>timeout</code></em> option
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync See also the <code class="option">-w</code> option.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync If <span class="command"><strong>host</strong></span> has been built with IDN (internationalized
d1966fe9681e9a100f8c895f08e450fc32dafd48vboxsync domain name) support, it can accept and display non-ASCII domain names.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync <span class="command"><strong>host</strong></span> appropriately converts character encoding of
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync domain name before sending a request to DNS server or displaying a
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync reply from the server.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync If you'd like to turn off the IDN support for some reason, defines
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync the <code class="envar">IDN_DISABLE</code> environment variable.
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync The IDN support is disabled if the variable is set when
b1d7d513c459787311cd09c440524044fa7ff8a9vboxsync <span class="command"><strong>host</strong></span> runs.