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<refentry xmlns="http://docbook.org/ns/docbook" version="5.0" xml:id="man.host">
  <info>
    <date>2009-01-20</date>
  </info>
  <refentryinfo>
    <corpname>ISC</corpname>
    <corpauthor>Internet Systems Consortium, Inc.</corpauthor>
  </refentryinfo>

  <refmeta>
    <refentrytitle>host</refentrytitle>
    <manvolnum>1</manvolnum>
    <refmiscinfo>BIND9</refmiscinfo>
  </refmeta>

  <refnamediv>
    <refname>host</refname>
    <refpurpose>DNS lookup utility</refpurpose>
  </refnamediv>

  <docinfo>
    <copyright>
      <year>2000</year>
      <year>2001</year>
      <year>2002</year>
      <year>2004</year>
      <year>2005</year>
      <year>2007</year>
      <year>2008</year>
      <year>2009</year>
      <year>2014</year>
      <year>2015</year>
      <year>2016</year>
      <holder>Internet Systems Consortium, Inc. ("ISC")</holder>
    </copyright>
  </docinfo>

  <refsynopsisdiv>
    <cmdsynopsis sepchar=" ">
      <command>host</command>
      <arg choice="opt" rep="norepeat"><option>-aCdlnrsTwv</option></arg>
      <arg choice="opt" rep="norepeat"><option>-c <replaceable class="parameter">class</replaceable></option></arg>
      <arg choice="opt" rep="norepeat"><option>-N <replaceable class="parameter">ndots</replaceable></option></arg>
      <arg choice="opt" rep="norepeat"><option>-R <replaceable class="parameter">number</replaceable></option></arg>
      <arg choice="opt" rep="norepeat"><option>-t <replaceable class="parameter">type</replaceable></option></arg>
      <arg choice="opt" rep="norepeat"><option>-W <replaceable class="parameter">wait</replaceable></option></arg>
      <arg choice="opt" rep="norepeat"><option>-m <replaceable class="parameter">flag</replaceable></option></arg>
      <arg choice="opt" rep="norepeat"><option>-4</option></arg>
      <arg choice="opt" rep="norepeat"><option>-6</option></arg>
      <arg choice="opt" rep="norepeat"><option>-v</option></arg>
      <arg choice="opt" rep="norepeat"><option>-V</option></arg>
      <arg choice="req" rep="norepeat">name</arg>
      <arg choice="opt" rep="norepeat">server</arg>
    </cmdsynopsis>
  </refsynopsisdiv>

  <refsection><info><title>DESCRIPTION</title></info>


    <para><command>host</command>
      is a simple utility for performing DNS lookups.
      It is normally used to convert names to IP addresses and vice versa.
      When no arguments or options are given,
      <command>host</command>
      prints a short summary of its command line arguments and options.
    </para>

    <para><parameter>name</parameter> is the domain name that is to be
      looked
      up.  It can also be a dotted-decimal IPv4 address or a colon-delimited
      IPv6 address, in which case <command>host</command> will by
      default
      perform a reverse lookup for that address.
      <parameter>server</parameter> is an optional argument which
      is either
      the name or IP address of the name server that <command>host</command>
      should query instead of the server or servers listed in
      <filename>/etc/resolv.conf</filename>.
    </para>

  </refsection>

  <refsection><info><title>OPTIONS</title></info>

    <variablelist>

      <varlistentry>
	<term>-4</term>
	<listitem>
	  <para>
	    Use IPv4 only for query transport.
	    See also the <option>-6</option> option.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-6</term>
	<listitem>
	  <para>
	    Use IPv6 only for query transport.
	    See also the <option>-4</option> option.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-a</term>
	<listitem>
	  <para>
	    "All". The <option>-a</option> option is normally equivalent
	    to <option>-v -t <literal>ANY</literal></option>.
	    It also affects the behaviour of the <option>-l</option>
	    list zone option.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-c <replaceable class="parameter">class</replaceable></term>
	<listitem>
	  <para>
	    Query class: This can be used to lookup HS (Hesiod) or CH
	    (Chaosnet) class resource records. The default class is IN
	    (Internet).
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-C</term>
	<listitem>
	  <para>
	    Check consistency: <command>host</command> will query the
	    SOA records for zone <parameter>name</parameter> 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.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-d</term>
	<listitem>
	  <para>
	    Print debugging traces.
	    Equivalent to the <option>-v</option> verbose option.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-i</term>
	<listitem>
	  <para>
	    Obsolete.
	    Use the IP6.INT domain for reverse lookups of IPv6
	    addresses as defined in RFC1886 and deprecated in RFC4159.
	    The default is to use IP6.ARPA as specified in RFC3596.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-l</term>
	<listitem>
	  <para>
	    List zone:
	    The <command>host</command> command performs a zone transfer of
	    zone <parameter>name</parameter> and prints out the NS,
	    PTR and address records (A/AAAA).
	  </para>
	  <para>
	    Together, the <option>-l -a</option>
	    options print all records in the zone.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-N <replaceable class="parameter">ndots</replaceable></term>
	<listitem>
	  <para>
	    The number of dots that have to be
	    in <parameter>name</parameter> for it to be considered
	    absolute. The default value is that defined using the
	    ndots statement in <filename>/etc/resolv.conf</filename>,
	    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 <type>search</type> or <type>domain</type> directive
	    in <filename>/etc/resolv.conf</filename>.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-r</term>
	<listitem>
	  <para>
	    Non-recursive query:
	    Setting this option clears the RD (recursion desired) bit
	    in the query. This should mean that the name server
	    receiving the query will not attempt to
	    resolve <parameter>name</parameter>.
	    The <option>-r</option> option
	    enables <command>host</command> to mimic the behavior of a
	    name server by making non-recursive queries and expecting
	    to receive answers to those queries that can be
	    referrals to other name servers.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-R <replaceable class="parameter">number</replaceable></term>
	<listitem>
	  <para>
	    Number of retries for UDP queries:
	    If <parameter>number</parameter> is negative or zero, the
	    number of retries will default to 1. The default value is
	    1, or the value of the <parameter>attempts</parameter>
	    option in <filename>/etc/resolv.conf</filename>, if set.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-s</term>
	<listitem>
	  <para>
	    Do <emphasis>not</emphasis> send the query to the next
	    nameserver if any server responds with a SERVFAIL
	    response, which is the reverse of normal stub resolver
	    behavior.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-t <replaceable class="parameter">type</replaceable></term>
	<listitem>
	  <para>
	    Query type:
	    The <parameter>type</parameter> argument can be any
	    recognized query type: CNAME, NS, SOA, TXT, DNSKEY, AXFR, etc.
	  </para>
	  <para>
	    When no query type is specified, <command>host</command>
	    automatically selects an appropriate query type. By default, it
	    looks for A, AAAA, and MX records.
	    If the <option>-C</option> option is given, queries will
	    be made for SOA records.
	    If <parameter>name</parameter> is a dotted-decimal IPv4
	    address or colon-delimited IPv6
	    address, <command>host</command> will query for PTR
	    records.
	  </para>
	  <para>
	    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
	    (like <option>-t <literal>IXFR=12345678</literal></option>).
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-T</term>
	<listitem>
	  <para>
	    TCP:
	    By default, <command>host</command> uses UDP when making
	    queries. The <option>-T</option> 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.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-m <replaceable class="parameter">flag</replaceable></term>
	<listitem>
	  <para>
	    Memory usage debugging: the flag can
	    be <parameter>record</parameter>, <parameter>usage</parameter>,
	    or <parameter>trace</parameter>. You can specify
	    the <option>-m</option> option more than once to set
	    multiple flags.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-v</term>
	<listitem>
	  <para>
	    Verbose output.
	    Equivalent to the <option>-d</option> debug option.
	    Verbose output can also be enabled by setting
	    the <parameter>debug</parameter> option
	    in <filename>/etc/resolv.conf</filename>.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-V</term>
	<listitem>
	  <para>
	    Print the version number and exit.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-w</term>
	<listitem>
	  <para>
	    Wait forever: The query timeout is set to the maximum possible.
	    See also the <option>-W</option> option.
	  </para>
	</listitem>
      </varlistentry>

      <varlistentry>
	<term>-W <replaceable class="parameter">wait</replaceable></term>
	<listitem>
	  <para>
	    Timeout: Wait for up to <parameter>wait</parameter>
	    seconds for a reply. If <parameter>wait</parameter> is
	    less than one, the wait interval is set to one second.
	  </para>
	  <para>
	    By default, <command>host</command> will wait for 5
	    seconds for UDP responses and 10 seconds for TCP
	    connections. These defaults can be overridden by
	    the <parameter>timeout</parameter> option
	    in <filename>/etc/resolv.conf</filename>.
	  </para>
	  <para>
	    See also the <option>-w</option> option.
	  </para>
	</listitem>
      </varlistentry>

    </variablelist>

  </refsection>

  <refsection><info><title>IDN SUPPORT</title></info>

    <para>
      If <command>host</command> has been built with IDN (internationalized
      domain name) support, it can accept and display non-ASCII domain names.
      <command>host</command> 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 <envar>IDN_DISABLE</envar> environment variable.
      The IDN support is disabled if the variable is set when
      <command>host</command> runs.
    </para>
  </refsection>

  <refsection><info><title>FILES</title></info>

    <para><filename>/etc/resolv.conf</filename>
    </para>
  </refsection>

  <refsection><info><title>SEE ALSO</title></info>

    <para><citerefentry>
        <refentrytitle>dig</refentrytitle><manvolnum>1</manvolnum>
      </citerefentry>,
      <citerefentry>
        <refentrytitle>named</refentrytitle><manvolnum>8</manvolnum>
      </citerefentry>.
    </para>
  </refsection>

</refentry>
