host






host − DNS lookup utility



host [ ‐aCdlnrTwv ]  [ ‐c class ]  [ ‐N ndots ]  [ ‐R number
]  [ ‐t type ]  [ ‐W wait ]  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. The argument is
provided for compatibility with older implementations. This
option is equivalent to making a query of type AXFR.

     The ‐n option specifies that reverse lookups of IPv6
addresses should use the IP6.INT domain and "nibble" labels
as defined in RFC1886.  The default is to use IP6.ARPA and
binary labels as defined in RFC2874.

     The ‐N option sets the number of dots that have to be
in name for it to be considered absolute. The default value









                             ‐2‐


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 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 ‐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.

     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.



     /etc/resolv.conf



     dig(1), named(8).