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<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry" title="host">
<div class="refnamediv">
<h2>Name</h2>
<p>
host
— DNS lookup utility
</p>
</div>
<div class="refsynopsisdiv" title="Synopsis">
<h2>Synopsis</h2>
<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>]
[<code class="option">-v</code>]
[<code class="option">-V</code>]
{name}
[server]
</p></div>
</div>
<div class="refsection" title="DESCRIPTION">
<a name="idp60917584"></a><h2>DESCRIPTION</h2>
<p><span class="command"><strong>host</strong></span>
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,
<span class="command"><strong>host</strong></span>
prints a short summary of its command line arguments and options.
</p>
<p><em class="parameter"><code>name</code></em> 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 <span class="command"><strong>host</strong></span> will by
default
perform a reverse lookup for that address.
<em class="parameter"><code>server</code></em> is an optional argument which
is either
the name or IP address of the name server that <span class="command"><strong>host</strong></span>
should query instead of the server or servers listed in
</p>
<p>
The <code class="option">-a</code> (all) option is equivalent to setting the
<code class="option">-v</code> option and asking <span class="command"><strong>host</strong></span> to make
a query of type ANY.
</p>
<p>
When the <code class="option">-C</code> option is used, <span class="command"><strong>host</strong></span>
will attempt to display the SOA records for zone
<em class="parameter"><code>name</code></em> 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.
</p>
<p>
The <code class="option">-c</code> option instructs to make a DNS query of class
<em class="parameter"><code>class</code></em>. This can be used to lookup
Hesiod or
Chaosnet class resource records. The default class is IN (Internet).
</p>
<p>
Verbose output is generated by <span class="command"><strong>host</strong></span> when
the
<code class="option">-d</code> or <code class="option">-v</code> option is used. The two
options are equivalent. They have been provided for backwards
compatibility. In previous versions, the <code class="option">-d</code> option
switched on debugging traces and <code class="option">-v</code> enabled verbose
output. Verbose output can also be enabled by setting the
<em class="parameter"><code>debug</code></em> option in
</p>
<p>
List mode is selected by the <code class="option">-l</code> option. This makes
<span class="command"><strong>host</strong></span> perform a zone transfer for zone
<em class="parameter"><code>name</code></em>. Transfer the zone printing out
the NS, PTR
all records will be printed.
</p>
<p>
The <code class="option">-i</code>
option specifies that reverse lookups of IPv6 addresses should
use the IP6.INT domain as defined in RFC1886.
The default is to use IP6.ARPA.
</p>
<p>
The <code class="option">-N</code> option sets the number of dots that have to be
in <em class="parameter"><code>name</code></em> for it to be considered
absolute. The
default value is that defined using the ndots statement in
statement is
present. Names with fewer dots are interpreted as relative names and
will be searched for in the domains listed in the <span class="type">search</span>
or <span class="type">domain</span> directive in
</p>
<p>
The number of UDP retries for a lookup can be changed with the
<code class="option">-R</code> option. <em class="parameter"><code>number</code></em>
indicates
how many times <span class="command"><strong>host</strong></span> will repeat a query
that does
not get answered. If
<em class="parameter"><code>number</code></em> is negative or zero, the
number of
retries will default to 1. The default value is 1, or
the value of the <em class="parameter"><code>attempts</code></em> option in
</p>
<p>
Non-recursive queries can be made via the <code class="option">-r</code> option.
Setting this option clears the <span class="type">RD</span> — recursion
desired — bit in the query which <span class="command"><strong>host</strong></span> makes.
This should mean that the name server receiving the query will not
attempt to resolve <em class="parameter"><code>name</code></em>. The
<code class="option">-r</code> option enables <span class="command"><strong>host</strong></span>
to mimic
the behavior of a name server by making non-recursive queries and
expecting to receive answers to those queries that are usually
referrals to other name servers.
</p>
<p>
By default, <span class="command"><strong>host</strong></span> uses UDP when making
queries. The
<code class="option">-T</code> 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.
</p>
<p>
The <code class="option">-4</code> option forces <span class="command"><strong>host</strong></span> to only
use IPv4 query transport. The <code class="option">-6</code> option forces
<span class="command"><strong>host</strong></span> to only use IPv6 query transport.
</p>
<p>
The <code class="option">-t</code> option is used to select the query type.
<em class="parameter"><code>type</code></em> can be any recognized query
type: CNAME,
NS, SOA, SIG, KEY, AXFR, etc. When no query type is specified,
<span class="command"><strong>host</strong></span> automatically selects an appropriate
query
type. By default, it looks for A, AAAA, and MX records, but if the
<code class="option">-C</code> option was given, queries will be made for SOA
records, and if <em class="parameter"><code>name</code></em> is a
dotted-decimal IPv4
address or colon-delimited IPv6 address, <span class="command"><strong>host</strong></span> will
query for PTR records. 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 (e.g. -t IXFR=12345678).
</p>
<p>
The time to wait for a reply can be controlled through the
<code class="option">-W</code> and <code class="option">-w</code> options. The
<code class="option">-W</code> option makes <span class="command"><strong>host</strong></span>
wait for
<em class="parameter"><code>wait</code></em> seconds. If <em class="parameter"><code>wait</code></em>
is less than one, the wait interval is set to one second. When the
<code class="option">-w</code> option is used, <span class="command"><strong>host</strong></span>
will
effectively wait forever for a reply. The time to wait for a response
will be set to the number of seconds given by the hardware's maximum
value for an integer quantity. By default, <span class="command"><strong>host</strong></span>
will wait for 5 seconds for UDP responses and 10 seconds for TCP
connections. These defaults can be overridden by the
<em class="parameter"><code>timeout</code></em> option in
</p>
<p>
The <code class="option">-s</code> option tells <span class="command"><strong>host</strong></span>
<span class="emphasis"><em>not</em></span> to send the query to the next nameserver
if any server responds with a SERVFAIL response, which is the
reverse of normal stub resolver behavior.
</p>
<p>
The <code class="option">-m</code> can be used to set the memory usage debugging
flags
<em class="parameter"><code>record</code></em>, <em class="parameter"><code>usage</code></em> and
<em class="parameter"><code>trace</code></em>.
</p>
<p>
The <code class="option">-V</code> option causes <span class="command"><strong>host</strong></span>
to print the version number and exit.
</p>
</div>
<div class="refsection" title="IDN SUPPORT">
<a name="idp60955984"></a><h2>IDN SUPPORT</h2>
<p>
If <span class="command"><strong>host</strong></span> has been built with IDN (internationalized
domain name) support, it can accept and display non-ASCII domain names.
<span class="command"><strong>host</strong></span> 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 <code class="envar">IDN_DISABLE</code> environment variable.
The IDN support is disabled if the variable is set when
<span class="command"><strong>host</strong></span> runs.
</p>
</div>
<div class="refsection" title="FILES">
<a name="idp60958928"></a><h2>FILES</h2>
</p>
</div>
<div class="refsection" title="SEE ALSO">
<a name="idp60960592"></a><h2>SEE ALSO</h2>
<p><span class="citerefentry">
<span class="refentrytitle">dig</span>(1)
</span>,
<span class="citerefentry">
<span class="refentrytitle">named</span>(8)
</span>.
</p>
</div>
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