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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>
<year>2017</year>
<year>2018</year>
<year>2019</year>
<year>2020</year>
<holder>Internet Systems Consortium, Inc. ("ISC")</holder>
</copyright>
</docinfo>
<refsynopsisdiv>
<cmdsynopsis sepchar=" ">
<command>host</command>
<arg choice="opt" rep="norepeat"><option>-aCdlnrsTUwv</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>-p <replaceable class="port">port</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>
<group choice="opt" rep="norepeat">
<arg choice="opt" rep="norepeat"><option>-4</option></arg>
<arg choice="opt" rep="norepeat"><option>-6</option></arg>
</group>
<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>-p <replaceable class="parameter">port</replaceable></term>
<listitem>
<para>
Specify the port on the server to query. The default is 53.
</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>
<term>-U</term>
<listitem>
<para>
TCP/UDP:
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. Type ANY queries default
to TCP but can be forced to UDP initially using <option>-U</option>.
</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>