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9afcd92352224325ed65919f69f7f58282fc6623Andreas Gustafsson<a name="man.host"></a><div class="titlepage"></div>
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bf6d2e39124ab3d51c253f7acad9a4abef059be6Bob Halley<h2>Name</h2>
bf6d2e39124ab3d51c253f7acad9a4abef059be6Bob Halley<p>host &#8212; DNS lookup utility</p>
ab023a65562e62b85a824509d829b6fad87e00b1Rob Austein</div>
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington<div class="refsynopsisdiv">
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington<h2>Synopsis</h2>
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington<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>
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington</div>
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington<div class="refsect1" lang="en">
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington<a name="id2615213"></a><h2>DESCRIPTION</h2>
01956482905dd861a9b07d417d469955466b728dDamien Neil<p><span><strong class="command">host</strong></span>
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil is a simple utility for performing DNS lookups.
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil It is normally used to convert names to IP addresses and vice versa.
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil When no arguments or options are given,
b2a6ebf1bd4dad1410afba9012a61d87090f03adDamien Neil <span><strong class="command">host</strong></span>
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil prints a short summary of its command line arguments and options.
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil </p>
ab023a65562e62b85a824509d829b6fad87e00b1Rob Austein<p><em class="parameter"><code>name</code></em> is the domain name that is to be
ab023a65562e62b85a824509d829b6fad87e00b1Rob Austein looked
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil up. It can also be a dotted-decimal IPv4 address or a colon-delimited
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil IPv6 address, in which case <span><strong class="command">host</strong></span> will by
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil default
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington perform a reverse lookup for that address.
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington <em class="parameter"><code>server</code></em> is an optional argument which
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil is either
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil the name or IP address of the name server that <span><strong class="command">host</strong></span>
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil should query instead of the server or servers listed in
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil <code class="filename">/etc/resolv.conf</code>.
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil </p>
8f7b56e275abdaaec08ccac32ffc6174841ae60eMichael Graff<p>
8f7b56e275abdaaec08ccac32ffc6174841ae60eMichael Graff The <code class="option">-a</code> (all) option is equivalent to setting the
8f7b56e275abdaaec08ccac32ffc6174841ae60eMichael Graff <code class="option">-v</code> option and asking <span><strong class="command">host</strong></span> to make
8f7b56e275abdaaec08ccac32ffc6174841ae60eMichael Graff a query of type ANY.
bf6d2e39124ab3d51c253f7acad9a4abef059be6Bob Halley </p>
18d0b5e54be891a1aa938c165b6d439859121ec8Mark Andrews<p>
18d0b5e54be891a1aa938c165b6d439859121ec8Mark Andrews When the <code class="option">-C</code> option is used, <span><strong class="command">host</strong></span>
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil will attempt to display the SOA records for zone
8f7b56e275abdaaec08ccac32ffc6174841ae60eMichael Graff <em class="parameter"><code>name</code></em> from all the listed
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington authoritative name
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington servers for that zone. The list of name servers is defined by the NS
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington records that are found for the zone.
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil </p>
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington<p>
bf6d2e39124ab3d51c253f7acad9a4abef059be6Bob Halley The <code class="option">-c</code> option instructs to make a DNS query of class
bf6d2e39124ab3d51c253f7acad9a4abef059be6Bob Halley <em class="parameter"><code>class</code></em>. This can be used to lookup
bf6d2e39124ab3d51c253f7acad9a4abef059be6Bob Halley Hesiod or
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington Chaosnet class resource records. The default class is IN (Internet).
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington </p>
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil<p>
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil Verbose output is generated by <span><strong class="command">host</strong></span> when
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil the
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil <code class="option">-d</code> or <code class="option">-v</code> option is used. The two
bf6d2e39124ab3d51c253f7acad9a4abef059be6Bob Halley options are equivalent. They have been provided for backwards
bf6d2e39124ab3d51c253f7acad9a4abef059be6Bob Halley compatibility. In previous versions, the <code class="option">-d</code> option
bf6d2e39124ab3d51c253f7acad9a4abef059be6Bob Halley switched on debugging traces and <code class="option">-v</code> enabled verbose
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil output. Verbose output can also be enabled by setting the
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil <em class="parameter"><code>debug</code></em> option in
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil <code class="filename">/etc/resolv.conf</code>.
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil </p>
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil<p>
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil List mode is selected by the <code class="option">-l</code> option. This makes
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil <span><strong class="command">host</strong></span> perform a zone transfer for zone
f671a5c51cc59e266620c0c4026b054908fdd80cBob Halley <em class="parameter"><code>name</code></em>. Transfer the zone printing out
e4b9761b0ef03597c35d1ef1d86e12514c621f90Michael Graff the NS, PTR
f671a5c51cc59e266620c0c4026b054908fdd80cBob Halley and address records (A/AAAA). If combined with <code class="option">-a</code>
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil all records will be printed.
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil </p>
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil<p>
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil The <code class="option">-i</code>
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil option specifies that reverse lookups of IPv6 addresses should
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil use the IP6.INT domain as defined in RFC1886.
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil The default is to use IP6.ARPA.
bf6d2e39124ab3d51c253f7acad9a4abef059be6Bob Halley </p>
bf6d2e39124ab3d51c253f7acad9a4abef059be6Bob Halley<p>
bf6d2e39124ab3d51c253f7acad9a4abef059be6Bob Halley The <code class="option">-N</code> option sets the number of dots that have to be
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil in <em class="parameter"><code>name</code></em> for it to be considered
bf6d2e39124ab3d51c253f7acad9a4abef059be6Bob Halley absolute. The
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington default value is that defined using the ndots statement in
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington <code class="filename">/etc/resolv.conf</code>, or 1 if no ndots
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington statement is
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington present. Names with fewer dots are interpreted as relative names and
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington will be searched for in the domains listed in the <span class="type">search</span>
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington or <span class="type">domain</span> directive in
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington <code class="filename">/etc/resolv.conf</code>.
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington </p>
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington<p>
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil The number of UDP retries for a lookup can be changed with the
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil <code class="option">-R</code> option. <em class="parameter"><code>number</code></em>
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil indicates
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil how many times <span><strong class="command">host</strong></span> will repeat a query
e9453d609db9aed9efd2bb4fd287ff3ad11da0b2Damien Neil that does
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington not get answered. If
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington <em class="parameter"><code>number</code></em> is negative or zero, the
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington number of
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington retries will default to 1. The default value is 1, or
8f7b56e275abdaaec08ccac32ffc6174841ae60eMichael Graff the value of the <em class="parameter"><code>attempts</code></em> option in
8f7b56e275abdaaec08ccac32ffc6174841ae60eMichael Graff <code class="filename">/etc/resolv.conf</code>, if set.
8f7b56e275abdaaec08ccac32ffc6174841ae60eMichael Graff </p>
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington<p>
26d20cd51c968e111b4122536825368a17b5ca82Brian Wellington Non-recursive queries can be made via the <code class="option">-r</code> option.
18d0b5e54be891a1aa938c165b6d439859121ec8Mark Andrews Setting this option clears the <span class="type">RD</span> &#8212; recursion
bf6d2e39124ab3d51c253f7acad9a4abef059be6Bob Halley desired &#8212; bit in the query which <span><strong class="command">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><strong class="command">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><strong class="command">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><strong class="command">host</strong></span> to only
use IPv4 query transport. The <code class="option">-6</code> option forces
<span><strong class="command">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><strong class="command">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><strong class="command">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><strong class="command">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><strong class="command">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><strong class="command">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
<code class="filename">/etc/resolv.conf</code>.
</p>
<p>
The <code class="option">-s</code> option tells <span><strong class="command">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><strong class="command">host</strong></span>
to print the version number and exit.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2617688"></a><h2>IDN SUPPORT</h2>
<p>
If <span><strong class="command">host</strong></span> has been built with IDN (internationalized
domain name) support, it can accept and display non-ASCII domain names.
<span><strong class="command">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><strong class="command">host</strong></span> runs.
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2617717"></a><h2>FILES</h2>
<p><code class="filename">/etc/resolv.conf</code>
</p>
</div>
<div class="refsect1" lang="en">
<a name="id2617731"></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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