\fBhost\fR 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, \fBhost\fR prints a short summary of its command line arguments and options\&.
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\fIname\fR 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 \fBhost\fR will by default perform a reverse lookup for that address\&. \fIserver\fR is an optional argument which is either the name or IP address of the name server that \fBhost\fR should query instead of the server or servers listed in \fI/etc/resolv\&.conf\fR\&.
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The \fB\-a\fR (all) option is equivalent to setting the \fB\-v\fR option and asking \fBhost\fR to make a query of type ANY\&.
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When the \fB\-C\fR option is used, \fBhost\fR will attempt to display the SOA records for zone \fIname\fR 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\&.
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The \fB\-c\fR option instructs to make a DNS query of class \fIclass\fR\&. This can be used to lookup Hesiod or Chaosnet class resource records\&. The default class is IN (Internet)\&.
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Verbose output is generated by \fBhost\fR when the \fB\-d\fR or \fB\-v\fR option is used\&. The two options are equivalent\&. They have been provided for backwards compatibility\&. In previous versions, the \fB\-d\fR option switched on debugging traces and \fB\-v\fR enabled verbose output\&.
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List mode is selected by the \fB\-l\fR option\&. This makes \fBhost\fR perform a zone transfer for zone \fIname\fR\&. Transfer the zone printing out the NS, PTR and address records (A/AAAA)\&. If combined with \fB\-a\fR all records will be printed\&.
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The \fB\-i\fR 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\&.
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The \fB\-N\fR option sets the number of dots that have to be in \fIname\fR for it to be considered absolute\&. The default value is that defined using the ndots statement in \fI/etc/resolv\&.conf\fR, 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 \fBsearch\fR or \fBdomain\fR directive in \fI/etc/resolv\&.conf\fR\&.
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The number of UDP retries for a lookup can be changed with the \fB\-R\fR option\&. \fInumber\fR indicates how many times \fBhost\fR will repeat a query that does not get answered\&. The default number of retries is 1\&. If \fInumber\fR is negative or zero, the number of retries will default to 1\&.
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Non\-recursive queries can be made via the \fB\-r\fR option\&. Setting this option clears the \fBRD\fR -- recursion desired -- bit in the query which \fBhost\fR makes\&. This should mean that the name server receiving the query will not attempt to resolve \fIname\fR\&. The \fB\-r\fR option enables \fBhost\fR 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\&.
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By default \fBhost\fR uses UDP when making queries\&. The \fB\-T\fR 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\&.
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The \fB\-4\fR option forces \fBhost\fR to only use IPv4 query transport\&. The \fB\-6\fR option forces \fBhost\fR to only use IPv6 query transport\&.
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The \fB\-t\fR option is used to select the query type\&. \fItype\fR can be any recognised query type: CNAME, NS, SOA, SIG, KEY, AXFR, etc\&. When no query type is specified, \fBhost\fR automatically selects an appropriate query type\&. By default it looks for A records, but if the \fB\-C\fR option was given, queries will be made for SOA records, and if \fIname\fR is a dotted\-decimal IPv4 address or colon\-delimited IPv6 address, \fBhost\fR 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)\&.
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The time to wait for a reply can be controlled through the \fB\-W\fR and \fB\-w\fR options\&. The \fB\-W\fR option makes \fBhost\fR wait for \fIwait\fR seconds\&. If \fIwait\fR is less than one, the wait interval is set to one second\&. When the \fB\-w\fR option is used, \fBhost\fR 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\&.
The \fB\-s\fR option tells \fBhost\fR\fInot\fR to send the query to the next nameserver if any server responds with a SERVFAIL response, which is the reverse of normal stub resolver behaviour\&.
If \fBhost\fR has been built with IDN (internationalized domain name) support, it can accept and display non\-ASCII domain names\&. \fBhost\fR appropriately converts character encoding of domain name before sending a request to DNS server or displaying a reply from the server\&. If you'd like to turn off the IDN support for some reason, defines the \fBIDN_DISABLE\fR environment variable\&. The IDN support is disabled if the variable is set when \fBhost\fR runs\&.
