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1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen - Copyright (C) 2004-2015 Internet Systems Consortium, Inc. ("ISC")
1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen - Copyright (C) 2000-2003 Internet Software Consortium.
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5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen - purpose with or without fee is hereby granted, provided that the above
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20b2d47ed762ca2c009aa37e360af6f223ac71bdTimo Sirainen<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>
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen<p><span><strong class="command">host</strong></span>
1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen is a simple utility for performing DNS lookups.
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen It is normally used to convert names to IP addresses and vice versa.
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen When no arguments or options are given,
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen <span><strong class="command">host</strong></span>
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen prints a short summary of its command line arguments and options.
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen<p><em class="parameter"><code>name</code></em> is the domain name that is to be
1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen up. It can also be a dotted-decimal IPv4 address or a colon-delimited
c2fbbf7515aa419dc8b2d62a3c2bb0471d51a391Timo Sirainen IPv6 address, in which case <span><strong class="command">host</strong></span> will by
20b2d47ed762ca2c009aa37e360af6f223ac71bdTimo Sirainen perform a reverse lookup for that address.
20b2d47ed762ca2c009aa37e360af6f223ac71bdTimo Sirainen <em class="parameter"><code>server</code></em> is an optional argument which
20b2d47ed762ca2c009aa37e360af6f223ac71bdTimo Sirainen the name or IP address of the name server that <span><strong class="command">host</strong></span>
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen should query instead of the server or servers listed in
20b2d47ed762ca2c009aa37e360af6f223ac71bdTimo Sirainen <code class="filename">/etc/resolv.conf</code>.
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen The <code class="option">-a</code> (all) option is equivalent to setting the
1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen <code class="option">-v</code> option and asking <span><strong class="command">host</strong></span> to make
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen a query of type ANY.
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen When the <code class="option">-C</code> option is used, <span><strong class="command">host</strong></span>
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen will attempt to display the SOA records for zone
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen <em class="parameter"><code>name</code></em> from all the listed
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen authoritative name
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen servers for that zone. The list of name servers is defined by the NS
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen records that are found for the zone.
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen The <code class="option">-c</code> option instructs to make a DNS query of class
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen <em class="parameter"><code>class</code></em>. This can be used to lookup
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen Chaosnet class resource records. The default class is IN (Internet).
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen Verbose output is generated by <span><strong class="command">host</strong></span> when
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen <code class="option">-d</code> or <code class="option">-v</code> option is used. The two
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen options are equivalent. They have been provided for backwards
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen compatibility. In previous versions, the <code class="option">-d</code> option
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen switched on debugging traces and <code class="option">-v</code> enabled verbose
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen output. Verbose output can also be enabled by setting the
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen <em class="parameter"><code>debug</code></em> option in
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen <code class="filename">/etc/resolv.conf</code>.
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen List mode is selected by the <code class="option">-l</code> option. This makes
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen <span><strong class="command">host</strong></span> perform a zone transfer for zone
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen <em class="parameter"><code>name</code></em>. Transfer the zone printing out
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen and address records (A/AAAA). If combined with <code class="option">-a</code>
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen all records will be printed.
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen option specifies that reverse lookups of IPv6 addresses should
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen use the IP6.INT domain as defined in RFC1886.
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen The default is to use IP6.ARPA.
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen The <code class="option">-N</code> option sets the number of dots that have to be
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen in <em class="parameter"><code>name</code></em> for it to be considered
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen absolute. The
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen default value is that defined using the ndots statement in
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen <code class="filename">/etc/resolv.conf</code>, or 1 if no ndots
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen present. Names with fewer dots are interpreted as relative names and
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen will be searched for in the domains listed in the <span class="type">search</span>
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen or <span class="type">domain</span> directive in
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen <code class="filename">/etc/resolv.conf</code>.
1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen The number of UDP retries for a lookup can be changed with the
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen <code class="option">-R</code> option. <em class="parameter"><code>number</code></em>
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen how many times <span><strong class="command">host</strong></span> will repeat a query
20b2d47ed762ca2c009aa37e360af6f223ac71bdTimo Sirainen not get answered. If
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen <em class="parameter"><code>number</code></em> is negative or zero, the
1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen retries will default to 1. The default value is 1, or
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen the value of the <em class="parameter"><code>attempts</code></em> option in
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen <code class="filename">/etc/resolv.conf</code>, if set.
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen Non-recursive queries can be made via the <code class="option">-r</code> option.
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen Setting this option clears the <span class="type">RD</span> — recursion
20b2d47ed762ca2c009aa37e360af6f223ac71bdTimo Sirainen desired — bit in the query which <span><strong class="command">host</strong></span> makes.
20b2d47ed762ca2c009aa37e360af6f223ac71bdTimo Sirainen This should mean that the name server receiving the query will not
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen attempt to resolve <em class="parameter"><code>name</code></em>. The
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen <code class="option">-r</code> option enables <span><strong class="command">host</strong></span>
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen the behavior of a name server by making non-recursive queries and
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen expecting to receive answers to those queries that are usually
5c2d695acf9f95ae0dcdda89c4d2391ceda4d672Timo Sirainen referrals to other name servers.
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen By default, <span><strong class="command">host</strong></span> uses UDP when making
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen <code class="option">-T</code> option makes it use a TCP connection when querying
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen the name server. TCP will be automatically selected for queries that
4fc52b7b25c3d3f42348903e0154840f8761f306Timo Sirainen require it, such as zone transfer (AXFR) requests.
1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen The <code class="option">-4</code> option forces <span><strong class="command">host</strong></span> to only
1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen use IPv4 query transport. The <code class="option">-6</code> option forces
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen <span><strong class="command">host</strong></span> to only use IPv6 query transport.
1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen The <code class="option">-t</code> option is used to select the query type.
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen <em class="parameter"><code>type</code></em> can be any recognized query
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen NS, SOA, SIG, KEY, AXFR, etc. When no query type is specified,
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen <span><strong class="command">host</strong></span> automatically selects an appropriate
896093ae6961612ac6ef8722d79dd457f1b43dd0Timo Sirainen type. By default, it looks for A, AAAA, and MX records, but if the
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen <code class="option">-C</code> option was given, queries will be made for SOA
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen records, and if <em class="parameter"><code>name</code></em> is a
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen dotted-decimal IPv4
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen address or colon-delimited IPv6 address, <span><strong class="command">host</strong></span> will
1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen query for PTR records. If a query type of IXFR is chosen the starting
1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen serial number can be specified by appending an equal followed by the
55058d5f50f7e53bb22df4fa6ae951c8001416abTimo Sirainen starting serial number (e.g. -t IXFR=12345678).
1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen The time to wait for a reply can be controlled through the
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen <code class="option">-W</code> and <code class="option">-w</code> options. The
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen <code class="option">-W</code> option makes <span><strong class="command">host</strong></span>
55058d5f50f7e53bb22df4fa6ae951c8001416abTimo Sirainen <em class="parameter"><code>wait</code></em> seconds. If <em class="parameter"><code>wait</code></em>
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen is less than one, the wait interval is set to one second. When the
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen <code class="option">-w</code> option is used, <span><strong class="command">host</strong></span>
55058d5f50f7e53bb22df4fa6ae951c8001416abTimo Sirainen effectively wait forever for a reply. The time to wait for a response
55058d5f50f7e53bb22df4fa6ae951c8001416abTimo Sirainen will be set to the number of seconds given by the hardware's maximum
55058d5f50f7e53bb22df4fa6ae951c8001416abTimo Sirainen value for an integer quantity. By default, <span><strong class="command">host</strong></span>
55058d5f50f7e53bb22df4fa6ae951c8001416abTimo Sirainen will wait for 5 seconds for UDP responses and 10 seconds for TCP
55058d5f50f7e53bb22df4fa6ae951c8001416abTimo Sirainen connections. These defaults can be overridden by the
55058d5f50f7e53bb22df4fa6ae951c8001416abTimo Sirainen <em class="parameter"><code>timeout</code></em> option in
1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen <code class="filename">/etc/resolv.conf</code>.
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen The <code class="option">-s</code> option tells <span><strong class="command">host</strong></span>
1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen <span class="emphasis"><em>not</em></span> to send the query to the next nameserver
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen if any server responds with a SERVFAIL response, which is the
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen reverse of normal stub resolver behavior.
c4b376dd6e0c423006d7ac83a39253bcaf8e7c47Timo Sirainen The <code class="option">-m</code> can be used to set the memory usage debugging
1176124297af5c56e932c0863c6637ff21d8a0efTimo Sirainen <em class="parameter"><code>record</code></em>, <em class="parameter"><code>usage</code></em> and