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f062ed7bd262a37a909dd77ce5fc23b446818823fielding<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>
7f235c0d101d71224c8e498ac8f7fde1f98596c7dgaudet<p><span><strong class="command">host</strong></span>
7f235c0d101d71224c8e498ac8f7fde1f98596c7dgaudet is a simple utility for performing DNS lookups.
7f235c0d101d71224c8e498ac8f7fde1f98596c7dgaudet It is normally used to convert names to IP addresses and vice versa.
7f235c0d101d71224c8e498ac8f7fde1f98596c7dgaudet When no arguments or options are given,
6e954603b02f2b7d4ad80af17d9b3cc6f0bacf69rbb prints a short summary of its command line arguments and options.
ff47cb235b4f43ef57b8b5e9f9775ea472e8afecrbb<p><em class="parameter"><code>name</code></em> is the domain name that is to be
ff47cb235b4f43ef57b8b5e9f9775ea472e8afecrbb up. It can also be a dotted-decimal IPv4 address or a colon-delimited
badd892102405c12e3a9216e67d199339bc80aaadgaudet IPv6 address, in which case <span><strong class="command">host</strong></span> will by
badd892102405c12e3a9216e67d199339bc80aaadgaudet perform a reverse lookup for that address.
badd892102405c12e3a9216e67d199339bc80aaadgaudet <em class="parameter"><code>server</code></em> is an optional argument which
badd892102405c12e3a9216e67d199339bc80aaadgaudet the name or IP address of the name server that <span><strong class="command">host</strong></span>
badd892102405c12e3a9216e67d199339bc80aaadgaudet should query instead of the server or servers listed in
cb5a017cbad1e36dc501d8afc65636b8c2edf2d8rbb The <code class="option">-a</code> (all) option is equivalent to setting the
badd892102405c12e3a9216e67d199339bc80aaadgaudet <code class="option">-v</code> option and asking <span><strong class="command">host</strong></span> to make
badd892102405c12e3a9216e67d199339bc80aaadgaudet a query of type ANY.
badd892102405c12e3a9216e67d199339bc80aaadgaudet When the <code class="option">-C</code> option is used, <span><strong class="command">host</strong></span>
badd892102405c12e3a9216e67d199339bc80aaadgaudet will attempt to display the SOA records for zone
badd892102405c12e3a9216e67d199339bc80aaadgaudet <em class="parameter"><code>name</code></em> from all the listed
badd892102405c12e3a9216e67d199339bc80aaadgaudet authoritative name
badd892102405c12e3a9216e67d199339bc80aaadgaudet servers for that zone. The list of name servers is defined by the NS
badd892102405c12e3a9216e67d199339bc80aaadgaudet records that are found for the zone.
badd892102405c12e3a9216e67d199339bc80aaadgaudet The <code class="option">-c</code> option instructs to make a DNS query of class
badd892102405c12e3a9216e67d199339bc80aaadgaudet <em class="parameter"><code>class</code></em>. This can be used to lookup
badd892102405c12e3a9216e67d199339bc80aaadgaudet Chaosnet class resource records. The default class is IN (Internet).
badd892102405c12e3a9216e67d199339bc80aaadgaudet Verbose output is generated by <span><strong class="command">host</strong></span> when
badd892102405c12e3a9216e67d199339bc80aaadgaudet <code class="option">-d</code> or <code class="option">-v</code> option is used. The two
badd892102405c12e3a9216e67d199339bc80aaadgaudet options are equivalent. They have been provided for backwards
badd892102405c12e3a9216e67d199339bc80aaadgaudet compatibility. In previous versions, the <code class="option">-d</code> option
badd892102405c12e3a9216e67d199339bc80aaadgaudet switched on debugging traces and <code class="option">-v</code> enabled verbose
badd892102405c12e3a9216e67d199339bc80aaadgaudet List mode is selected by the <code class="option">-l</code> option. This makes
443f96ac390c06ca4fa763d3bfcfbc8f757bd756rbb <span><strong class="command">host</strong></span> perform a zone transfer for zone
badd892102405c12e3a9216e67d199339bc80aaadgaudet <em class="parameter"><code>name</code></em>. Transfer the zone printing out
badd892102405c12e3a9216e67d199339bc80aaadgaudet the NS, PTR
badd892102405c12e3a9216e67d199339bc80aaadgaudet and address records (A/AAAA). If combined with <code class="option">-a</code>
b29f87f4b6c6886a04dccc296177a7033f70dfedtrawick all records will be printed.
ff47cb235b4f43ef57b8b5e9f9775ea472e8afecrbb option specifies that reverse lookups of IPv6 addresses should
ff47cb235b4f43ef57b8b5e9f9775ea472e8afecrbb use the IP6.INT domain as defined in RFC1886.
ff47cb235b4f43ef57b8b5e9f9775ea472e8afecrbb The default is to use IP6.ARPA.
ff47cb235b4f43ef57b8b5e9f9775ea472e8afecrbb The <code class="option">-N</code> option sets the number of dots that have to be
ff47cb235b4f43ef57b8b5e9f9775ea472e8afecrbb in <em class="parameter"><code>name</code></em> for it to be considered
1ccd992d37d62c8cb2056126f2234f64ec189bfddougm absolute. The
ff47cb235b4f43ef57b8b5e9f9775ea472e8afecrbb default value is that defined using the ndots statement in
3d96ee83babeec32482c9082c9426340cee8c44dwrowe <code class="filename">/etc/resolv.conf</code>, or 1 if no ndots
7f235c0d101d71224c8e498ac8f7fde1f98596c7dgaudet statement is
ff47cb235b4f43ef57b8b5e9f9775ea472e8afecrbb present. Names with fewer dots are interpreted as relative names and
ff47cb235b4f43ef57b8b5e9f9775ea472e8afecrbb will be searched for in the domains listed in the <span class="type">search</span>
3d96ee83babeec32482c9082c9426340cee8c44dwrowe The number of UDP retries for a lookup can be changed with the
7f235c0d101d71224c8e498ac8f7fde1f98596c7dgaudet <code class="option">-R</code> option. <em class="parameter"><code>number</code></em>
39813b8983b16dce75194e7b70184fd68743db90manoj how many times <span><strong class="command">host</strong></span> will repeat a query
39813b8983b16dce75194e7b70184fd68743db90manoj not get answered. The default number of retries is 1. If
39813b8983b16dce75194e7b70184fd68743db90manoj <em class="parameter"><code>number</code></em> is negative or zero, the
39813b8983b16dce75194e7b70184fd68743db90manoj retries will default to 1.
39813b8983b16dce75194e7b70184fd68743db90manoj Non-recursive queries can be made via the <code class="option">-r</code> option.
39813b8983b16dce75194e7b70184fd68743db90manoj Setting this option clears the <span class="type">RD</span> — recursion
39813b8983b16dce75194e7b70184fd68743db90manoj desired — bit in the query which <span><strong class="command">host</strong></span> makes.
39813b8983b16dce75194e7b70184fd68743db90manoj This should mean that the name server receiving the query will not
cccd31fa4a72fe23cc3249c06db181b274a55a69gstein attempt to resolve <em class="parameter"><code>name</code></em>. The
cccd31fa4a72fe23cc3249c06db181b274a55a69gstein <code class="option">-r</code> option enables <span><strong class="command">host</strong></span>
cccd31fa4a72fe23cc3249c06db181b274a55a69gstein the behavior of a name server by making non-recursive queries and
cccd31fa4a72fe23cc3249c06db181b274a55a69gstein expecting to receive answers to those queries that are usually
cccd31fa4a72fe23cc3249c06db181b274a55a69gstein referrals to other name servers.
39813b8983b16dce75194e7b70184fd68743db90manoj By default <span><strong class="command">host</strong></span> uses UDP when making
e195f530289a532984788547fc22ef4d1d1995berbb queries. The
e195f530289a532984788547fc22ef4d1d1995berbb <code class="option">-T</code> option makes it use a TCP connection when querying
e195f530289a532984788547fc22ef4d1d1995berbb the name server. TCP will be automatically selected for queries that
e195f530289a532984788547fc22ef4d1d1995berbb require it, such as zone transfer (AXFR) requests.
e195f530289a532984788547fc22ef4d1d1995berbb The <code class="option">-4</code> option forces <span><strong class="command">host</strong></span> to only
e195f530289a532984788547fc22ef4d1d1995berbb use IPv4 query transport. The <code class="option">-6</code> option forces
e195f530289a532984788547fc22ef4d1d1995berbb <span><strong class="command">host</strong></span> to only use IPv6 query transport.
29a9516d4b69977a36f4c93119ffcbec9809b044trawick The <code class="option">-t</code> option is used to select the query type.
29a9516d4b69977a36f4c93119ffcbec9809b044trawick <em class="parameter"><code>type</code></em> can be any recognized query
29a9516d4b69977a36f4c93119ffcbec9809b044trawick type: CNAME,
29a9516d4b69977a36f4c93119ffcbec9809b044trawick NS, SOA, SIG, KEY, AXFR, etc. When no query type is specified,
29a9516d4b69977a36f4c93119ffcbec9809b044trawick <span><strong class="command">host</strong></span> automatically selects an appropriate
f44d73842e45390adaecf468eb99d6654e29c33dwrowe type. By default it looks for A, AAAA, and MX records, but if the
f44d73842e45390adaecf468eb99d6654e29c33dwrowe <code class="option">-C</code> option was given, queries will be made for SOA
c4fbc4018fd2b6716673a38ee27eeb36cba41c5djwoolley records, and if <em class="parameter"><code>name</code></em> is a
f44d73842e45390adaecf468eb99d6654e29c33dwrowe dotted-decimal IPv4
ed4f9ec869d7fc5bd220c8d70ee58eed9b32d60arederpj address or colon-delimited IPv6 address, <span><strong class="command">host</strong></span> will
c4fbc4018fd2b6716673a38ee27eeb36cba41c5djwoolley query for PTR records. If a query type of IXFR is chosen the starting
f44d73842e45390adaecf468eb99d6654e29c33dwrowe serial number can be specified by appending an equal followed by the
f44d73842e45390adaecf468eb99d6654e29c33dwrowe starting serial number (e.g. -t IXFR=12345678).
ed4f9ec869d7fc5bd220c8d70ee58eed9b32d60arederpj The time to wait for a reply can be controlled through the
29a9516d4b69977a36f4c93119ffcbec9809b044trawick <code class="option">-W</code> and <code class="option">-w</code> options. The
9a0d076511763b559a755133f6a182e6c24ef643rbb <code class="option">-W</code> option makes <span><strong class="command">host</strong></span>
9a0d076511763b559a755133f6a182e6c24ef643rbb <em class="parameter"><code>wait</code></em> seconds. If <em class="parameter"><code>wait</code></em>
9a0d076511763b559a755133f6a182e6c24ef643rbb is less than one, the wait interval is set to one second. When the
9a0d076511763b559a755133f6a182e6c24ef643rbb <code class="option">-w</code> option is used, <span><strong class="command">host</strong></span>
9a0d076511763b559a755133f6a182e6c24ef643rbb effectively wait forever for a reply. The time to wait for a response
9a0d076511763b559a755133f6a182e6c24ef643rbb will be set to the number of seconds given by the hardware's maximum
9a0d076511763b559a755133f6a182e6c24ef643rbb value for an integer quantity.
752ab911a1a7fd6ce297a5f38b80ad38cc70c8f3dougm The <code class="option">-s</code> option tells <span><strong class="command">host</strong></span>
752ab911a1a7fd6ce297a5f38b80ad38cc70c8f3dougm <span class="emphasis"><em>not</em></span> to send the query to the next nameserver
752ab911a1a7fd6ce297a5f38b80ad38cc70c8f3dougm if any server responds with a SERVFAIL response, which is the
752ab911a1a7fd6ce297a5f38b80ad38cc70c8f3dougm reverse of normal stub resolver behavior.
752ab911a1a7fd6ce297a5f38b80ad38cc70c8f3dougm The <code class="option">-m</code> can be used to set the memory usage debugging
752ab911a1a7fd6ce297a5f38b80ad38cc70c8f3dougm <em class="parameter"><code>record</code></em>, <em class="parameter"><code>usage</code></em> and
5866fd6f9cba06306e84d940fc29973e50001b51trawick If <span><strong class="command">host</strong></span> has been built with IDN (internationalized
5866fd6f9cba06306e84d940fc29973e50001b51trawick domain name) support, it can accept and display non-ASCII domain names.
5866fd6f9cba06306e84d940fc29973e50001b51trawick <span><strong class="command">host</strong></span> appropriately converts character encoding of
5866fd6f9cba06306e84d940fc29973e50001b51trawick domain name before sending a request to DNS server or displaying a
5866fd6f9cba06306e84d940fc29973e50001b51trawick reply from the server.
5866fd6f9cba06306e84d940fc29973e50001b51trawick If you'd like to turn off the IDN support for some reason, defines
5866fd6f9cba06306e84d940fc29973e50001b51trawick the <code class="envar">IDN_DISABLE</code> environment variable.
7f235c0d101d71224c8e498ac8f7fde1f98596c7dgaudet The IDN support is disabled if the variable is set when