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  21. <title>host</title>
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    31. 

  31. <tr><th colspan="3" align="center">host</th></tr>
    32. 

  32. <tr>
    33. 

  33. <td width="20%" align="left">
    34. 

  34. <a accesskey="p" href="man.dig.html">Prev</a> </td>
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  42. <div class="refentry" lang="en">
    43. 

  43. <a name="man.host"></a><div class="titlepage"></div>
    44. 

  44. <div class="refnamediv">
    45. 

  45. <h2>Name</h2>
    46. 

  46. <p>host &#8212; DNS lookup utility</p>
    47. 

  47. </div>
    48. 

  48. <div class="refsynopsisdiv">
    49. 

  49. <h2>Synopsis</h2>
    50. 

  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. 

  51. </div>
    52. 

  52. <div class="refsect1" lang="en">
    53. 

  53. <a name="id2611091"></a><h2>DESCRIPTION</h2>
    54. 

  54. <p><span><strong class="command">host</strong></span>
    55. 

  55.       is a simple utility for performing DNS lookups.
    56. 

  56.       It is normally used to convert names to IP addresses and vice versa.
    57. 

  57.       When no arguments or options are given,
    58. 

  58.       <span><strong class="command">host</strong></span>
    59. 

  59.       prints a short summary of its command line arguments and options.
    60. 

  60.     </p>
    61. 

  61. <p><em class="parameter"><code>name</code></em> is the domain name that is to be
    62. 

  62.       looked
    63. 

  63.       up.  It can also be a dotted-decimal IPv4 address or a colon-delimited
    64. 

  64.       IPv6 address, in which case <span><strong class="command">host</strong></span> will by
    65. 

  65.       default
    66. 

  66.       perform a reverse lookup for that address.
    67. 

  67.       <em class="parameter"><code>server</code></em> is an optional argument which
    68. 

  68.       is either
    69. 

  69.       the name or IP address of the name server that <span><strong class="command">host</strong></span>
    70. 

  70.       should query instead of the server or servers listed in
    71. 

  71.       <code class="filename">/etc/resolv.conf</code>.
    72. 

  72.     </p>
    73. 

  73. <p>
    74. 

  74.       The <code class="option">-a</code> (all) option is equivalent to setting the
    75. 

  75.       <code class="option">-v</code> option and asking <span><strong class="command">host</strong></span> to make
    76. 

  76.       a query of type ANY.
    77. 

  77.     </p>
    78. 

  78. <p>
    79. 

  79.       When the <code class="option">-C</code> option is used, <span><strong class="command">host</strong></span>
    80. 

  80.       will attempt to display the SOA records for zone
    81. 

  81.       <em class="parameter"><code>name</code></em> from all the listed
    82. 

  82.       authoritative name
    83. 

  83.       servers for that zone.  The list of name servers is defined by the NS
    84. 

  84.       records that are found for the zone.
    85. 

  85.     </p>
    86. 

  86. <p>
    87. 

  87.       The <code class="option">-c</code> option instructs to make a DNS query of class
    88. 

  88.       <em class="parameter"><code>class</code></em>.  This can be used to lookup
    89. 

  89.       Hesiod or
    90. 

  90.       Chaosnet class resource records.  The default class is IN (Internet).
    91. 

  91.     </p>
    92. 

  92. <p>
    93. 

  93.       Verbose output is generated by <span><strong class="command">host</strong></span> when
    94. 

  94.       the
    95. 

  95.       <code class="option">-d</code> or <code class="option">-v</code> option is used.  The two
    96. 

  96.       options are equivalent.  They have been provided for backwards
    97. 

  97.       compatibility.  In previous versions, the <code class="option">-d</code> option
    98. 

  98.       switched on debugging traces and <code class="option">-v</code> enabled verbose
    99. 

  99.       output.
    100. 

  100.     </p>
    101. 

  101. <p>
    102. 

  102.       List mode is selected by the <code class="option">-l</code> option.  This makes
    103. 

  103.       <span><strong class="command">host</strong></span> perform a zone transfer for zone
    104. 

  104.       <em class="parameter"><code>name</code></em>.  Transfer the zone printing out
    105. 

  105.       the NS, PTR
    106. 

  106.       and address records (A/AAAA).  If combined with <code class="option">-a</code>
    107. 

  107.       all records will be printed.
    108. 

  108.     </p>
    109. 

  109. <p>
    110. 

  110.       The <code class="option">-i</code>
    111. 

  111.       option specifies that reverse lookups of IPv6 addresses should
    112. 

  112.       use the IP6.INT domain as defined in RFC1886.
    113. 

  113.       The default is to use IP6.ARPA.
    114. 

  114.     </p>
    115. 

  115. <p>
    116. 

  116.       The <code class="option">-N</code> option sets the number of dots that have to be
    117. 

  117.       in <em class="parameter"><code>name</code></em> for it to be considered
    118. 

  118.       absolute.  The
    119. 

  119.       default value is that defined using the ndots statement in
    120. 

  120.       <code class="filename">/etc/resolv.conf</code>, or 1 if no ndots
    121. 

  121.       statement is
    122. 

  122.       present.  Names with fewer dots are interpreted as relative names and
    123. 

  123.       will be searched for in the domains listed in the <span class="type">search</span>
    124. 

  124.       or <span class="type">domain</span> directive in
    125. 

  125.       <code class="filename">/etc/resolv.conf</code>.
    126. 

  126.     </p>
    127. 

  127. <p>
    128. 

  128.       The number of UDP retries for a lookup can be changed with the
    129. 

  129.       <code class="option">-R</code> option.  <em class="parameter"><code>number</code></em>
    130. 

  130.       indicates
    131. 

  131.       how many times <span><strong class="command">host</strong></span> will repeat a query
    132. 

  132.       that does
    133. 

  133.       not get answered.  The default number of retries is 1.  If
    134. 

  134.       <em class="parameter"><code>number</code></em> is negative or zero, the
    135. 

  135.       number of
    136. 

  136.       retries will default to 1.
    137. 

  137.     </p>
    138. 

  138. <p>
    139. 

  139.       Non-recursive queries can be made via the <code class="option">-r</code> option.
    140. 

  140.       Setting this option clears the <span class="type">RD</span> &#8212; recursion
    141. 

  141.       desired &#8212; bit in the query which <span><strong class="command">host</strong></span> makes.
    142. 

  142.       This should mean that the name server receiving the query will not
    143. 

  143.       attempt to resolve <em class="parameter"><code>name</code></em>.  The
    144. 

  144.       <code class="option">-r</code> option enables <span><strong class="command">host</strong></span>
    145. 

  145.       to mimic
    146. 

  146.       the behavior of a name server by making non-recursive queries and
    147. 

  147.       expecting to receive answers to those queries that are usually
    148. 

  148.       referrals to other name servers.
    149. 

  149.     </p>
    150. 

  150. <p>
    151. 

  151.       By default, <span><strong class="command">host</strong></span> uses UDP when making
    152. 

  152.       queries.  The
    153. 

  153.       <code class="option">-T</code> option makes it use a TCP connection when querying
    154. 

  154.       the name server.  TCP will be automatically selected for queries that
    155. 

  155.       require it, such as zone transfer (AXFR) requests.
    156. 

  156.     </p>
    157. 

  157. <p>
    158. 

  158.       The <code class="option">-4</code> option forces <span><strong class="command">host</strong></span> to only
    159. 

  159.       use IPv4 query transport.  The <code class="option">-6</code> option forces
    160. 

  160.       <span><strong class="command">host</strong></span> to only use IPv6 query transport.
    161. 

  161.     </p>
    162. 

  162. <p>
    163. 

  163.       The <code class="option">-t</code> option is used to select the query type.
    164. 

  164.       <em class="parameter"><code>type</code></em> can be any recognized query
    165. 

  165.       type: CNAME,
    166. 

  166.       NS, SOA, SIG, KEY, AXFR, etc.  When no query type is specified,
    167. 

  167.       <span><strong class="command">host</strong></span> automatically selects an appropriate
    168. 

  168.       query
    169. 

  169.       type.  By default, it looks for A, AAAA, and MX records, but if the
    170. 

  170.       <code class="option">-C</code> option was given, queries will be made for SOA
    171. 

  171.       records, and if <em class="parameter"><code>name</code></em> is a
    172. 

  172.       dotted-decimal IPv4
    173. 

  173.       address or colon-delimited IPv6 address, <span><strong class="command">host</strong></span> will
    174. 

  174.       query for PTR records.  If a query type of IXFR is chosen the starting
    175. 

  175.       serial number can be specified by appending an equal followed by the
    176. 

  176.       starting serial number (e.g. -t IXFR=12345678).
    177. 

  177.     </p>
    178. 

  178. <p>
    179. 

  179.       The time to wait for a reply can be controlled through the
    180. 

  180.       <code class="option">-W</code> and <code class="option">-w</code> options.  The
    181. 

  181.       <code class="option">-W</code> option makes <span><strong class="command">host</strong></span>
    182. 

  182.       wait for
    183. 

  183.       <em class="parameter"><code>wait</code></em> seconds.  If <em class="parameter"><code>wait</code></em>
    184. 

  184.       is less than one, the wait interval is set to one second.  When the
    185. 

  185.       <code class="option">-w</code> option is used, <span><strong class="command">host</strong></span>
    186. 

  186.       will
    187. 

  187.       effectively wait forever for a reply.  The time to wait for a response
    188. 

  188.       will be set to the number of seconds given by the hardware's maximum
    189. 

  189.       value for an integer quantity.
    190. 

  190.     </p>
    191. 

  191. <p>
    192. 

  192.       The <code class="option">-s</code> option tells <span><strong class="command">host</strong></span> 
    193. 

  193.       <span class="emphasis"><em>not</em></span> to send the query to the next nameserver
    194. 

  194.       if any server responds with a SERVFAIL response, which is the
    195. 

  195.       reverse of normal stub resolver behavior.
    196. 

  196.     </p>
    197. 

  197. <p>
    198. 

  198.       The <code class="option">-m</code> can be used to set the memory usage debugging
    199. 

  199.       flags
    200. 

  200.       <em class="parameter"><code>record</code></em>, <em class="parameter"><code>usage</code></em> and
    201. 

  201.       <em class="parameter"><code>trace</code></em>.
    202. 

  202.     </p>
    203. 

  203. </div>
    204. 

  204. <div class="refsect1" lang="en">
    205. 

  205. <a name="id2611537"></a><h2>IDN SUPPORT</h2>
    206. 

  206. <p>
    207. 

  207.       If <span><strong class="command">host</strong></span> has been built with IDN (internationalized
    208. 

  208.       domain name) support, it can accept and display non-ASCII domain names. 
    209. 

  209.       <span><strong class="command">host</strong></span> appropriately converts character encoding of
    210. 

  210.       domain name before sending a request to DNS server or displaying a
    211. 

  211.       reply from the server.
    212. 

  212.       If you'd like to turn off the IDN support for some reason, defines
    213. 

  213.       the <code class="envar">IDN_DISABLE</code> environment variable.
    214. 

  214.       The IDN support is disabled if the variable is set when
    215. 

  215.       <span><strong class="command">host</strong></span> runs.
    216. 

  216.     </p>
    217. 

  217. </div>
    218. 

  218. <div class="refsect1" lang="en">
    219. 

  219. <a name="id2611565"></a><h2>FILES</h2>
    220. 

  220. <p><code class="filename">/etc/resolv.conf</code>
    221. 

  221.     </p>
    222. 

  222. </div>
    223. 

  223. <div class="refsect1" lang="en">
    224. 

  224. <a name="id2611579"></a><h2>SEE ALSO</h2>
    225. 

  225. <p><span class="citerefentry"><span class="refentrytitle">dig</span>(1)</span>,
    226. 

  226.       <span class="citerefentry"><span class="refentrytitle">named</span>(8)</span>.
    227. 

  227.     </p>
    228. 

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    229. 

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