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
/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 -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.
BIND 9.10.2rc2