host - phpMan

HOST(1) HOST(1)

NAME
host - DNS lookup utility

SYNOPSIS
host [ -aCdlnrTwv ] [ -c class ] [ -N ndots ] [ -R number ] [ -t type ] [ -W
wait ] [ -4 ] [ -6 ] [ -s ] name [ server ]

DESCRIPTION
host is a simple utility for performing DNS lookups. It is normally used to con-
vert 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 (Inter-
net).

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 ver-
bose 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 consid-
ered 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 behaviour of a name server by making non-recursive
queries and expecting to receive answers to those queries that are usually refer-
rals to other name servers.

By default host uses UDP when making queries. The -T option makes it use a TCP con-
nection 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 recognised 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 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
behaviour.

FILES
/etc/resolv.conf