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host - DNS lookup utility


host [-aCdlnrsTwv] [-c class] [-N ndots] [-R number] [-t type] [-W wait] [-m flag] [-4]
[-6] [-v] [-V] {name} [server]


host 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, host prints a
short summary of its command line arguments and options.

name 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 host will by default perform a
reverse lookup for that address. server is an optional argument which is either the name
or IP address of the name server that host should query instead of the server or servers
listed in /etc/resolv.conf.

The -a (all) option is equivalent to setting the -v option and asking host to make a query
of type ANY.

When the -C option is used, host will attempt to display the SOA records for zone name
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.

The -c option instructs to make a DNS query of class class. This can be used to lookup
Hesiod or Chaosnet class resource records. The default class is IN (Internet).

Verbose output is generated by host when the -d or -v option is used. The two options are
equivalent. They have been provided for backwards compatibility. In previous versions, the
-d option switched on debugging traces and -v enabled verbose output.

List mode is selected by the -l option. This makes host perform a zone transfer for zone
name. Transfer the zone printing out the NS, PTR and address records (A/AAAA). If combined
with -a all records will be printed.

The -i 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.

The -N option sets the number of dots that have to be in name for it to be considered
absolute. The default value is that defined using the ndots statement in /etc/resolv.conf,
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 search or domain directive in

The number of UDP retries for a lookup can be changed with the -R option. number
indicates how many times host will repeat a query that does not get answered. The default
number of retries is 1. If number is negative or zero, the number of retries will default
to 1.

Non-recursive queries can be made via the -r option. Setting this option clears the RD
recursion desired — bit in the query which host makes. This should mean that the name
server receiving the query will not attempt to resolve name. The -r option enables host to
mimic the behavior 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.

By default, host uses UDP when making queries. The -T 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.

The -4 option forces host to only use IPv4 query transport. The -6 option forces host to
only use IPv6 query transport.

The -t option is used to select the query type. type can be any recognized query type:
CNAME, NS, SOA, SIG, KEY, AXFR, etc. When no query type is specified, host automatically
selects an appropriate query type. By default, it looks for A, AAAA, and MX records, but
if the -C option was given, queries will be made for SOA records, and if name is a
dotted-decimal IPv4 address or colon-delimited IPv6 address, host 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).

The time to wait for a reply can be controlled through the -W and -w options. The -W
option makes host wait for wait seconds. If wait is less than one, the wait interval is
set to one second. When the -w option is used, host 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 -s option tells host not to send the query to the next nameserver if any server
responds with a SERVFAIL response, which is the reverse of normal stub resolver behavior.

The -m can be used to set the memory usage debugging flags record, usage and trace.

The -V option causes host to print the version number and exit.


If host has been built with IDN (internationalized domain name) support, it can accept and
display non-ASCII domain names. host 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 IDN_DISABLE
environment variable. The IDN support is disabled if the variable is set when host runs.

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