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 42<div class="refentry" lang="en">
 43<a name="man.host"></a><div class="titlepage"></div>
 44<div class="refnamediv">
 45<h2>Name</h2>
 46<p>host &#8212; DNS lookup utility</p>
 47</div>
 48<div class="refsynopsisdiv">
 49<h2>Synopsis</h2>
 50<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>] {name} [server]</p></div>
 51</div>
 52<div class="refsect1" lang="en">
 53<a name="id2611091"></a><h2>DESCRIPTION</h2>
 54<p><span><strong class="command">host</strong></span>
 55      is a simple utility for performing DNS lookups.
 56      It is normally used to convert names to IP addresses and vice versa.
 57      When no arguments or options are given,
 58      <span><strong class="command">host</strong></span>
 59      prints a short summary of its command line arguments and options.
 60    </p>
 61<p><em class="parameter"><code>name</code></em> is the domain name that is to be
 62      looked
 63      up.  It can also be a dotted-decimal IPv4 address or a colon-delimited
 64      IPv6 address, in which case <span><strong class="command">host</strong></span> will by
 65      default
 66      perform a reverse lookup for that address.
 67      <em class="parameter"><code>server</code></em> is an optional argument which
 68      is either
 69      the name or IP address of the name server that <span><strong class="command">host</strong></span>
 70      should query instead of the server or servers listed in
 71      <code class="filename">/etc/resolv.conf</code>.
 72    </p>
 73<p>
 74      The <code class="option">-a</code> (all) option is equivalent to setting the
 75      <code class="option">-v</code> option and asking <span><strong class="command">host</strong></span> to make
 76      a query of type ANY.
 77    </p>
 78<p>
 79      When the <code class="option">-C</code> option is used, <span><strong class="command">host</strong></span>
 80      will attempt to display the SOA records for zone
 81      <em class="parameter"><code>name</code></em> from all the listed
 82      authoritative name
 83      servers for that zone.  The list of name servers is defined by the NS
 84      records that are found for the zone.
 85    </p>
 86<p>
 87      The <code class="option">-c</code> option instructs to make a DNS query of class
 88      <em class="parameter"><code>class</code></em>.  This can be used to lookup
 89      Hesiod or
 90      Chaosnet class resource records.  The default class is IN (Internet).
 91    </p>
 92<p>
 93      Verbose output is generated by <span><strong class="command">host</strong></span> when
 94      the
 95      <code class="option">-d</code> or <code class="option">-v</code> option is used.  The two
 96      options are equivalent.  They have been provided for backwards
 97      compatibility.  In previous versions, the <code class="option">-d</code> option
 98      switched on debugging traces and <code class="option">-v</code> enabled verbose
 99      output.
100    </p>
101<p>
102      List mode is selected by the <code class="option">-l</code> option.  This makes
103      <span><strong class="command">host</strong></span> perform a zone transfer for zone
104      <em class="parameter"><code>name</code></em>.  Transfer the zone printing out
105      the NS, PTR
106      and address records (A/AAAA).  If combined with <code class="option">-a</code>
107      all records will be printed.
108    </p>
109<p>
110      The <code class="option">-i</code>
111      option specifies that reverse lookups of IPv6 addresses should
112      use the IP6.INT domain as defined in RFC1886.
113      The default is to use IP6.ARPA.
114    </p>
115<p>
116      The <code class="option">-N</code> option sets the number of dots that have to be
117      in <em class="parameter"><code>name</code></em> for it to be considered
118      absolute.  The
119      default value is that defined using the ndots statement in
120      <code class="filename">/etc/resolv.conf</code>, or 1 if no ndots
121      statement is
122      present.  Names with fewer dots are interpreted as relative names and
123      will be searched for in the domains listed in the <span class="type">search</span>
124      or <span class="type">domain</span> directive in
125      <code class="filename">/etc/resolv.conf</code>.
126    </p>
127<p>
128      The number of UDP retries for a lookup can be changed with the
129      <code class="option">-R</code> option.  <em class="parameter"><code>number</code></em>
130      indicates
131      how many times <span><strong class="command">host</strong></span> will repeat a query
132      that does
133      not get answered.  The default number of retries is 1.  If
134      <em class="parameter"><code>number</code></em> is negative or zero, the
135      number of
136      retries will default to 1.
137    </p>
138<p>
139      Non-recursive queries can be made via the <code class="option">-r</code> option.
140      Setting this option clears the <span class="type">RD</span> &#8212; recursion
141      desired &#8212; bit in the query which <span><strong class="command">host</strong></span> makes.
142      This should mean that the name server receiving the query will not
143      attempt to resolve <em class="parameter"><code>name</code></em>.  The
144      <code class="option">-r</code> option enables <span><strong class="command">host</strong></span>
145      to mimic
146      the behavior of a name server by making non-recursive queries and
147      expecting to receive answers to those queries that are usually
148      referrals to other name servers.
149    </p>
150<p>
151      By default, <span><strong class="command">host</strong></span> uses UDP when making
152      queries.  The
153      <code class="option">-T</code> option makes it use a TCP connection when querying
154      the name server.  TCP will be automatically selected for queries that
155      require it, such as zone transfer (AXFR) requests.
156    </p>
157<p>
158      The <code class="option">-4</code> option forces <span><strong class="command">host</strong></span> to only
159      use IPv4 query transport.  The <code class="option">-6</code> option forces
160      <span><strong class="command">host</strong></span> to only use IPv6 query transport.
161    </p>
162<p>
163      The <code class="option">-t</code> option is used to select the query type.
164      <em class="parameter"><code>type</code></em> can be any recognized query
165      type: CNAME,
166      NS, SOA, SIG, KEY, AXFR, etc.  When no query type is specified,
167      <span><strong class="command">host</strong></span> automatically selects an appropriate
168      query
169      type.  By default, it looks for A, AAAA, and MX records, but if the
170      <code class="option">-C</code> option was given, queries will be made for SOA
171      records, and if <em class="parameter"><code>name</code></em> is a
172      dotted-decimal IPv4
173      address or colon-delimited IPv6 address, <span><strong class="command">host</strong></span> will
174      query for PTR records.  If a query type of IXFR is chosen the starting
175      serial number can be specified by appending an equal followed by the
176      starting serial number (e.g. -t IXFR=12345678).
177    </p>
178<p>
179      The time to wait for a reply can be controlled through the
180      <code class="option">-W</code> and <code class="option">-w</code> options.  The
181      <code class="option">-W</code> option makes <span><strong class="command">host</strong></span>
182      wait for
183      <em class="parameter"><code>wait</code></em> seconds.  If <em class="parameter"><code>wait</code></em>
184      is less than one, the wait interval is set to one second.  When the
185      <code class="option">-w</code> option is used, <span><strong class="command">host</strong></span>
186      will
187      effectively wait forever for a reply.  The time to wait for a response
188      will be set to the number of seconds given by the hardware's maximum
189      value for an integer quantity.
190    </p>
191<p>
192      The <code class="option">-s</code> option tells <span><strong class="command">host</strong></span> 
193      <span class="emphasis"><em>not</em></span> to send the query to the next nameserver
194      if any server responds with a SERVFAIL response, which is the
195      reverse of normal stub resolver behavior.
196    </p>
197<p>
198      The <code class="option">-m</code> can be used to set the memory usage debugging
199      flags
200      <em class="parameter"><code>record</code></em>, <em class="parameter"><code>usage</code></em> and
201      <em class="parameter"><code>trace</code></em>.
202    </p>
203</div>
204<div class="refsect1" lang="en">
205<a name="id2611537"></a><h2>IDN SUPPORT</h2>
206<p>
207      If <span><strong class="command">host</strong></span> has been built with IDN (internationalized
208      domain name) support, it can accept and display non-ASCII domain names. 
209      <span><strong class="command">host</strong></span> appropriately converts character encoding of
210      domain name before sending a request to DNS server or displaying a
211      reply from the server.
212      If you'd like to turn off the IDN support for some reason, defines
213      the <code class="envar">IDN_DISABLE</code> environment variable.
214      The IDN support is disabled if the variable is set when
215      <span><strong class="command">host</strong></span> runs.
216    </p>
217</div>
218<div class="refsect1" lang="en">
219<a name="id2611565"></a><h2>FILES</h2>
220<p><code class="filename">/etc/resolv.conf</code>
221    </p>
222</div>
223<div class="refsect1" lang="en">
224<a name="id2611579"></a><h2>SEE ALSO</h2>
225<p><span class="citerefentry"><span class="refentrytitle">dig</span>(1)</span>,
226      <span class="citerefentry"><span class="refentrytitle">named</span>(8)</span>.
227    </p>
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