host - DNS lookup utility at Linux.org

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HOST(1) BIND9 HOST(1)

NAME
host - DNS lookup utility

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

DESCRIPTION
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 /etc/resolv.conf.

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 -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.

IDN SUPPORT
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.

FILES
/etc/resolv.conf