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24 <body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="refentry" lang="en">
25 <a name="man.host"></a><div class="titlepage"></div>
26 <div class="refnamediv">
28 <p>host — DNS lookup utility</p>
30 <div class="refsynopsisdiv">
32 <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>
34 <div class="refsect1" lang="en">
35 <a name="id2543436"></a><h2>DESCRIPTION</h2>
36 <p><span><strong class="command">host</strong></span>
37 is a simple utility for performing DNS lookups.
38 It is normally used to convert names to IP addresses and vice versa.
39 When no arguments or options are given,
40 <span><strong class="command">host</strong></span>
41 prints a short summary of its command line arguments and options.
43 <p><em class="parameter"><code>name</code></em> is the domain name that is to be
45 up. It can also be a dotted-decimal IPv4 address or a colon-delimited
46 IPv6 address, in which case <span><strong class="command">host</strong></span> will by
48 perform a reverse lookup for that address.
49 <em class="parameter"><code>server</code></em> is an optional argument which
51 the name or IP address of the name server that <span><strong class="command">host</strong></span>
52 should query instead of the server or servers listed in
53 <code class="filename">/etc/resolv.conf</code>.
56 The <code class="option">-a</code> (all) option is equivalent to setting the
57 <code class="option">-v</code> option and asking <span><strong class="command">host</strong></span> to make
61 When the <code class="option">-C</code> option is used, <span><strong class="command">host</strong></span>
62 will attempt to display the SOA records for zone
63 <em class="parameter"><code>name</code></em> from all the listed
65 servers for that zone. The list of name servers is defined by the NS
66 records that are found for the zone.
69 The <code class="option">-c</code> option instructs to make a DNS query of class
70 <em class="parameter"><code>class</code></em>. This can be used to lookup
72 Chaosnet class resource records. The default class is IN (Internet).
75 Verbose output is generated by <span><strong class="command">host</strong></span> when
77 <code class="option">-d</code> or <code class="option">-v</code> option is used. The two
78 options are equivalent. They have been provided for backwards
79 compatibility. In previous versions, the <code class="option">-d</code> option
80 switched on debugging traces and <code class="option">-v</code> enabled verbose
84 List mode is selected by the <code class="option">-l</code> option. This makes
85 <span><strong class="command">host</strong></span> perform a zone transfer for zone
86 <em class="parameter"><code>name</code></em>. Transfer the zone printing out
88 and address records (A/AAAA). If combined with <code class="option">-a</code>
89 all records will be printed.
92 The <code class="option">-i</code>
93 option specifies that reverse lookups of IPv6 addresses should
94 use the IP6.INT domain as defined in RFC1886.
95 The default is to use IP6.ARPA.
98 The <code class="option">-N</code> option sets the number of dots that have to be
99 in <em class="parameter"><code>name</code></em> for it to be considered
101 default value is that defined using the ndots statement in
102 <code class="filename">/etc/resolv.conf</code>, or 1 if no ndots
104 present. Names with fewer dots are interpreted as relative names and
105 will be searched for in the domains listed in the <span class="type">search</span>
106 or <span class="type">domain</span> directive in
107 <code class="filename">/etc/resolv.conf</code>.
110 The number of UDP retries for a lookup can be changed with the
111 <code class="option">-R</code> option. <em class="parameter"><code>number</code></em>
113 how many times <span><strong class="command">host</strong></span> will repeat a query
115 not get answered. The default number of retries is 1. If
116 <em class="parameter"><code>number</code></em> is negative or zero, the
118 retries will default to 1.
121 Non-recursive queries can be made via the <code class="option">-r</code> option.
122 Setting this option clears the <span class="type">RD</span> — recursion
123 desired — bit in the query which <span><strong class="command">host</strong></span> makes.
124 This should mean that the name server receiving the query will not
125 attempt to resolve <em class="parameter"><code>name</code></em>. The
126 <code class="option">-r</code> option enables <span><strong class="command">host</strong></span>
128 the behavior of a name server by making non-recursive queries and
129 expecting to receive answers to those queries that are usually
130 referrals to other name servers.
133 By default, <span><strong class="command">host</strong></span> uses UDP when making
135 <code class="option">-T</code> option makes it use a TCP connection when querying
136 the name server. TCP will be automatically selected for queries that
137 require it, such as zone transfer (AXFR) requests.
140 The <code class="option">-4</code> option forces <span><strong class="command">host</strong></span> to only
141 use IPv4 query transport. The <code class="option">-6</code> option forces
142 <span><strong class="command">host</strong></span> to only use IPv6 query transport.
145 The <code class="option">-t</code> option is used to select the query type.
146 <em class="parameter"><code>type</code></em> can be any recognized query
148 NS, SOA, SIG, KEY, AXFR, etc. When no query type is specified,
149 <span><strong class="command">host</strong></span> automatically selects an appropriate
151 type. By default, it looks for A, AAAA, and MX records, but if the
152 <code class="option">-C</code> option was given, queries will be made for SOA
153 records, and if <em class="parameter"><code>name</code></em> is a
155 address or colon-delimited IPv6 address, <span><strong class="command">host</strong></span> will
156 query for PTR records. If a query type of IXFR is chosen the starting
157 serial number can be specified by appending an equal followed by the
158 starting serial number (e.g. -t IXFR=12345678).
161 The time to wait for a reply can be controlled through the
162 <code class="option">-W</code> and <code class="option">-w</code> options. The
163 <code class="option">-W</code> option makes <span><strong class="command">host</strong></span>
165 <em class="parameter"><code>wait</code></em> seconds. If <em class="parameter"><code>wait</code></em>
166 is less than one, the wait interval is set to one second. When the
167 <code class="option">-w</code> option is used, <span><strong class="command">host</strong></span>
169 effectively wait forever for a reply. The time to wait for a response
170 will be set to the number of seconds given by the hardware's maximum
171 value for an integer quantity.
174 The <code class="option">-s</code> option tells <span><strong class="command">host</strong></span>
175 <span class="emphasis"><em>not</em></span> to send the query to the next nameserver
176 if any server responds with a SERVFAIL response, which is the
177 reverse of normal stub resolver behavior.
180 The <code class="option">-m</code> can be used to set the memory usage debugging
182 <em class="parameter"><code>record</code></em>, <em class="parameter"><code>usage</code></em> and
183 <em class="parameter"><code>trace</code></em>.
186 <div class="refsect1" lang="en">
187 <a name="id2543802"></a><h2>IDN SUPPORT</h2>
189 If <span><strong class="command">host</strong></span> has been built with IDN (internationalized
190 domain name) support, it can accept and display non-ASCII domain names.
191 <span><strong class="command">host</strong></span> appropriately converts character encoding of
192 domain name before sending a request to DNS server or displaying a
193 reply from the server.
194 If you'd like to turn off the IDN support for some reason, defines
195 the <code class="envar">IDN_DISABLE</code> environment variable.
196 The IDN support is disabled if the variable is set when
197 <span><strong class="command">host</strong></span> runs.
200 <div class="refsect1" lang="en">
201 <a name="id2543825"></a><h2>FILES</h2>
202 <p><code class="filename">/etc/resolv.conf</code>
205 <div class="refsect1" lang="en">
206 <a name="id2543836"></a><h2>SEE ALSO</h2>
207 <p><span class="citerefentry"><span class="refentrytitle">dig</span>(1)</span>,
208 <span class="citerefentry"><span class="refentrytitle">named</span>(8)</span>.