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><HEAD
><TITLE
>host</TITLE
><META
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><H1
><A
NAME="AEN1"
></A
>host</H1
><DIV
CLASS="REFNAMEDIV"
><A
NAME="AEN8"
></A
><H2
>Name</H2
>host -- DNS lookup utility</DIV
><DIV
CLASS="REFSYNOPSISDIV"
><A
NAME="AEN11"
></A
><H2
>Synopsis</H2
><P
><B
CLASS="COMMAND"
>host</B
> [<VAR
CLASS="OPTION"
>-aCdlnrTwv</VAR
>] [<VAR
CLASS="OPTION"
>-c <VAR
CLASS="REPLACEABLE"
>class</VAR
></VAR
>] [<VAR
CLASS="OPTION"
>-N <VAR
CLASS="REPLACEABLE"
>ndots</VAR
></VAR
>] [<VAR
CLASS="OPTION"
>-R <VAR
CLASS="REPLACEABLE"
>number</VAR
></VAR
>] [<VAR
CLASS="OPTION"
>-t <VAR
CLASS="REPLACEABLE"
>type</VAR
></VAR
>] [<VAR
CLASS="OPTION"
>-W <VAR
CLASS="REPLACEABLE"
>wait</VAR
></VAR
>] [<VAR
CLASS="OPTION"
>-4</VAR
>] [<VAR
CLASS="OPTION"
>-6</VAR
>] {name} [server]</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN37"
></A
><H2
>DESCRIPTION</H2
><P
><B
CLASS="COMMAND"
>host</B
>
is a simple utility for performing DNS lookups.
It is normally used to convert names to IP addresses and vice versa.
When no arguments or options are given,
<B
CLASS="COMMAND"
>host</B
>
prints a short summary of its command line arguments and options.</P
><P
><VAR
CLASS="PARAMETER"
>name</VAR
> is the domain name that is to be looked
up. It can also be a dotted-decimal IPv4 address or a colon-delimited
IPv6 address, in which case <B
CLASS="COMMAND"
>host</B
> will by default
perform a reverse lookup for that address.
<VAR
CLASS="PARAMETER"
>server</VAR
> is an optional argument which is either
the name or IP address of the name server that <B
CLASS="COMMAND"
>host</B
>
should query instead of the server or servers listed in
<TT
CLASS="FILENAME"
>/etc/resolv.conf</TT
>.</P
><P
>The <VAR
CLASS="OPTION"
>-a</VAR
> (all) option is equivalent to setting the
<VAR
CLASS="OPTION"
>-v</VAR
> option and asking <B
CLASS="COMMAND"
>host</B
> to make
a query of type ANY.</P
><P
>When the <VAR
CLASS="OPTION"
>-C</VAR
> option is used, <B
CLASS="COMMAND"
>host</B
>
will attempt to display the SOA records for zone
<VAR
CLASS="PARAMETER"
>name</VAR
> from all the listed authoritative name
servers for that zone. The list of name servers is defined by the NS
records that are found for the zone.</P
><P
>The <VAR
CLASS="OPTION"
>-c</VAR
> option instructs to make a DNS query of class
<VAR
CLASS="PARAMETER"
>class</VAR
>. This can be used to lookup Hesiod or
Chaosnet class resource records. The default class is IN (Internet).</P
><P
>Verbose output is generated by <B
CLASS="COMMAND"
>host</B
> when the
<VAR
CLASS="OPTION"
>-d</VAR
> or <VAR
CLASS="OPTION"
>-v</VAR
> option is used. The two
options are equivalent. They have been provided for backwards
compatibility. In previous versions, the <VAR
CLASS="OPTION"
>-d</VAR
> option
switched on debugging traces and <VAR
CLASS="OPTION"
>-v</VAR
> enabled verbose
output.</P
><P
>List mode is selected by the <VAR
CLASS="OPTION"
>-l</VAR
> option. This makes
<B
CLASS="COMMAND"
>host</B
> perform a zone transfer for zone
<VAR
CLASS="PARAMETER"
>name</VAR
>. Transfer the zone printing out the NS, PTR
and address records (A/AAAA). If combined with <VAR
CLASS="OPTION"
>-a</VAR
>
all records will be printed. </P
><P
>The <VAR
CLASS="OPTION"
>-i</VAR
>
option specifies that reverse lookups of IPv6 addresses should
use the IP6.INT domain as defined in RFC1886.
The default is to use IP6.ARPA.</P
><P
>The <VAR
CLASS="OPTION"
>-N</VAR
> option sets the number of dots that have to be
in <VAR
CLASS="PARAMETER"
>name</VAR
> for it to be considered absolute. The
default value is that defined using the ndots statement in
<TT
CLASS="FILENAME"
>/etc/resolv.conf</TT
>, or 1 if no ndots statement is
present. Names with fewer dots are interpreted as relative names and
will be searched for in the domains listed in the <SPAN
CLASS="TYPE"
>search</SPAN
>
or <SPAN
CLASS="TYPE"
>domain</SPAN
> directive in
<TT
CLASS="FILENAME"
>/etc/resolv.conf</TT
>.</P
><P
>The number of UDP retries for a lookup can be changed with the
<VAR
CLASS="OPTION"
>-R</VAR
> option. <VAR
CLASS="PARAMETER"
>number</VAR
> indicates
how many times <B
CLASS="COMMAND"
>host</B
> will repeat a query that does
not get answered. The default number of retries is 1. If
<VAR
CLASS="PARAMETER"
>number</VAR
> is negative or zero, the number of
retries will default to 1.</P
><P
>Non-recursive queries can be made via the <VAR
CLASS="OPTION"
>-r</VAR
> option.
Setting this option clears the <SPAN
CLASS="TYPE"
>RD</SPAN
> — recursion
desired — bit in the query which <B
CLASS="COMMAND"
>host</B
> makes.
This should mean that the name server receiving the query will not
attempt to resolve <VAR
CLASS="PARAMETER"
>name</VAR
>. The
<VAR
CLASS="OPTION"
>-r</VAR
> option enables <B
CLASS="COMMAND"
>host</B
> to mimic
the behaviour of a name server by making non-recursive queries and
expecting to receive answers to those queries that are usually
referrals to other name servers.</P
><P
>By default <B
CLASS="COMMAND"
>host</B
> uses UDP when making queries. The
<VAR
CLASS="OPTION"
>-T</VAR
> option makes it use a TCP connection when querying
the name server. TCP will be automatically selected for queries that
require it, such as zone transfer (AXFR) requests.</P
><P
>The <VAR
CLASS="OPTION"
>-4</VAR
> option forces <B
CLASS="COMMAND"
>host</B
> to only
use IPv4 query transport. The <VAR
CLASS="OPTION"
>-6</VAR
> option forces
<B
CLASS="COMMAND"
>host</B
> to only use IPv6 query transport.</P
><P
>The <VAR
CLASS="OPTION"
>-t</VAR
> option is used to select the query type.
<VAR
CLASS="PARAMETER"
>type</VAR
> can be any recognised query type: CNAME,
NS, SOA, SIG, KEY, AXFR, etc. When no query type is specified,
<B
CLASS="COMMAND"
>host</B
> automatically selects an appropriate query
type. By default it looks for A records, but if the
<VAR
CLASS="OPTION"
>-C</VAR
> option was given, queries will be made for SOA
records, and if <VAR
CLASS="PARAMETER"
>name</VAR
> is a dotted-decimal IPv4
address or colon-delimited IPv6 address, <B
CLASS="COMMAND"
>host</B
> will
query for PTR records. If a query type of IXFR is chosen the starting
serial number can be specified by appending an equal followed by the
starting serial number (e.g. -t IXFR=12345678).</P
><P
>The time to wait for a reply can be controlled through the
<VAR
CLASS="OPTION"
>-W</VAR
> and <VAR
CLASS="OPTION"
>-w</VAR
> options. The
<VAR
CLASS="OPTION"
>-W</VAR
> option makes <B
CLASS="COMMAND"
>host</B
> wait for
<VAR
CLASS="PARAMETER"
>wait</VAR
> seconds. If <VAR
CLASS="PARAMETER"
>wait</VAR
>
is less than one, the wait interval is set to one second. When the
<VAR
CLASS="OPTION"
>-w</VAR
> option is used, <B
CLASS="COMMAND"
>host</B
> will
effectively wait forever for a reply. The time to wait for a response
will be set to the number of seconds given by the hardware's maximum
value for an integer quantity.</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN115"
></A
><H2
>FILES</H2
><P
><TT
CLASS="FILENAME"
>/etc/resolv.conf</TT
></P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN119"
></A
><H2
>SEE ALSO</H2
><P
><SPAN
CLASS="CITEREFENTRY"
><SPAN
CLASS="REFENTRYTITLE"
>dig</SPAN
>(1)</SPAN
>,
<SPAN
CLASS="CITEREFENTRY"
><SPAN
CLASS="REFENTRYTITLE"
>named</SPAN
>(8)</SPAN
>.</P
></DIV
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></HTML
>
