NAME

host - DNS lookup utility

SYNOPSIS

hhoosstt [--aaCCddllnnrrssTTwwvv] [--cc _c_l_a_s_s] [--NN _n_d_o_t_s] [--RR _n_u_m_b_e_r] [--tt _t_y_p_e] [--WW _w_a_i_t] [--mm _f_l_a_g] [--44] [--66] {name} [server]

DESCRIPTION

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

_n_a_m_e 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 hhoosstt will by default perform a reverse lookup for that address. _s_e_r_v_e_r is an optional argument which is either the name or IP address of the name server that hhoosstt should query instead of the server or servers listed in _/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f.

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

When the --CC option is used, hhoosstt will attempt to display the SOA records for zone _n_a_m_e 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 --cc option instructs to make a DNS query of class _c_l_a_s_s. This can be used to lookup Hesiod or Chaosnet class resource records. The default class is IN (Internet).

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

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

The --ii 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 --NN option sets the number of dots that have to be in _n_a_m_e for it to be considered absolute. The default value is that defined using the ndots statement in _/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f, 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 sseeaarrcchh or ddoommaaiinn directive in _/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f.

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

Non-recursive queries can be made via the --rr option. Setting this option clears the RRDD -- recursion desired -- bit in the query which hhoosstt makes. This should mean that the name server receiving the query will not attempt to resolve _n_a_m_e. The --rr option enables hhoosstt 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, hhoosstt uses UDP when making queries. The --TT 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 --44 option forces hhoosstt to only use IPv4 query transport. The --66 option forces hhoosstt to only use IPv6 query transport.

The --tt option is used to select the query type. _t_y_p_e can be any recognized query type: CNAME, NS, SOA, SIG, KEY, AXFR, etc. When no query type is specified, hhoosstt automatically selects an appropriate query type. By default, it looks for A, AAAA, and MX records, but if the --CC option was given, queries will be made for SOA records, and if _n_a_m_e is a dotted-decimal IPv4 address or colon-delimited IPv6 address, hhoosstt 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 --WW and --ww options. The --WW option makes hhoosstt wait for _w_a_i_t seconds. If _w_a_i_t is less than one, the wait interval is set to one second. When the --ww option is used, hhoosstt 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 --ss option tells hhoosstt _n_o_t 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 --mm can be used to set the memory usage debugging flags _r_e_c_o_r_d, _u_s_a_g_e and _t_r_a_c_e.

IDN SUPPORT

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

FILES

_/_e_t_c_/_r_e_s_o_l_v_._c_o_n_f

SEE ALSO

ddiigg(1), nnaammeedd(8).

Copyright © 2004, 2005, 2007-2009 Internet Systems Consortium, Inc. ("ISC")
Copyright © 2000-2002 Internet Software Consortium.