.. Copyright (C) Internet Systems Consortium, Inc. ("ISC") .. .. SPDX-License-Identifier: MPL-2.0 .. .. This Source Code Form is subject to the terms of the Mozilla Public .. License, v. 2.0. If a copy of the MPL was not distributed with this .. file, you can obtain one at https://mozilla.org/MPL/2.0/. .. .. See the COPYRIGHT file distributed with this work for additional .. information regarding copyright ownership. .. highlight: console .. iscman:: host .. program:: host .. _man_host: host - DNS lookup utility ------------------------- Synopsis ~~~~~~~~ :program:`host` [**-aACdlnrsTUwv**] [**-c** class] [**-N** ndots] [**-p** port] [**-R** number] [**-t** type] [**-W** wait] [**-m** flag] [ [**-4**] | [**-6**] ] [**-v**] [**-V**] {name} [server] Description ~~~~~~~~~~~ :program:`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, :program:`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 :program:`host` by default performs a reverse lookup for that address. ``server`` is an optional argument which is either the name or IP address of the name server that :program:`host` should query instead of the server or servers listed in ``/etc/resolv.conf``. Options ~~~~~~~ .. option:: -4 This option specifies that only IPv4 should be used for query transport. See also the :option:`-6` option. .. option:: -6 This option specifies that only IPv6 should be used for query transport. See also the :option:`-4` option. .. option:: -a The :option:`-a` ("all") option is normally equivalent to :option:`-v` :option:`-t ANY <-t>`. It also affects the behavior of the :option:`-l` list zone option. .. option:: -A The :option:`-A` ("almost all") option is equivalent to :option:`-a`, except that RRSIG, NSEC, and NSEC3 records are omitted from the output. .. option:: -c class This option specifies the query class, which can be used to lookup HS (Hesiod) or CH (Chaosnet) class resource records. The default class is IN (Internet). .. option:: -C This option indicates that :iscman:`named` should check consistency, meaning that :program:`host` queries 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. .. option:: -d This option prints debugging traces, and is equivalent to the :option:`-v` verbose option. .. option:: -l This option tells :iscman:`named` to list the zone, meaning the :program:`host` command performs a zone transfer of zone ``name`` and prints out the NS, PTR, and address records (A/AAAA). Together, the :option:`-l` :option:`-a` options print all records in the zone. .. option:: -N ndots This option specifies the number of dots (``ndots``) 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 are searched for in the domains listed in the ``search`` or ``domain`` directive in ``/etc/resolv.conf``. .. option:: -p port This option specifies the port to query on the server. The default is 53. .. option:: -r This option specifies a non-recursive query; setting this option clears the RD (recursion desired) bit in the query. This means that the name server receiving the query does not attempt to resolve ``name``. The :option:`-r` option enables :program:`host` to mimic the behavior of a name server by making non-recursive queries, and expecting to receive answers to those queries that can be referrals to other name servers. .. option:: -R number This option specifies the number of retries for UDP queries. If ``number`` is negative or zero, the number of retries is silently set to 1. The default value is 1, or the value of the ``attempts`` option in ``/etc/resolv.conf``, if set. .. option:: -s This option tells :iscman:`named` *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. .. option:: -t type This option specifies the query type. The ``type`` argument can be any recognized query type: CNAME, NS, SOA, TXT, DNSKEY, AXFR, etc. When no query type is specified, :program:`host` automatically selects an appropriate query type. By default, it looks for A, AAAA, and MX records. If the :option:`-C` option is given, queries are made for SOA records. If ``name`` is a dotted-decimal IPv4 address or colon-delimited IPv6 address, :program:`host` queries for PTR records. If a query type of IXFR is chosen, the starting serial number can be specified by appending an equals sign (=), followed by the starting serial number, e.g., :option:`-t IXFR=12345678 <-t>`. .. option:: -T, -U This option specifies TCP or UDP. By default, :program:`host` uses UDP when making queries; the :option:`-T` option makes it use a TCP connection when querying the name server. TCP is automatically selected for queries that require it, such as zone transfer (AXFR) requests. Type ``ANY`` queries default to TCP, but can be forced to use UDP initially via :option:`-U`. .. option:: -m flag This option sets memory usage debugging: the flag can be ``record``, ``usage``, or ``trace``. The :option:`-m` option can be specified more than once to set multiple flags. .. option:: -v This option sets verbose output, and is equivalent to the :option:`-d` debug option. Verbose output can also be enabled by setting the ``debug`` option in ``/etc/resolv.conf``. .. option:: -V This option prints the version number and exits. .. option:: -w This option sets "wait forever": the query timeout is set to the maximum possible. See also the :option:`-W` option. .. option:: -W wait This options sets the length of the wait timeout, indicating that :iscman:`named` should wait for up to ``wait`` seconds for a reply. If ``wait`` is less than 1, the wait interval is set to 1 second. By default, :program:`host` waits for 5 seconds for UDP responses and 10 seconds for TCP connections. These defaults can be overridden by the ``timeout`` option in ``/etc/resolv.conf``. See also the :option:`-w` option. IDN Support ~~~~~~~~~~~ If :program:`host` has been built with IDN (internationalized domain name) support, it can accept and display non-ASCII domain names. :program:`host` appropriately converts character encoding of a domain name before sending a request to a DNS server or displaying a reply from the server. To turn off IDN support, define the ``IDN_DISABLE`` environment variable. IDN support is disabled if the variable is set when :program:`host` runs. Files ~~~~~ ``/etc/resolv.conf`` See Also ~~~~~~~~ :iscman:`dig(1) `, :iscman:`named(8) `.