host - DNS lookup utility
host [
-aACdlnrsTUwv] [
-c class] [
-N ndots]
[
-p port] [
-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 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
host should query instead of the server or
servers listed in
/etc/resolv.conf.
- -4
- This option specifies that only IPv4 should be used for
query transport. See also the -6 option.
- -6
- This option specifies that only IPv6 should be used for
query transport. See also the -4 option.
- -a
- The -a ("all") option is normally
equivalent to -v -t ANY. It also affects the behavior of the
-l list zone option.
- -A
- The -A ("almost all") option is equivalent
to -a, except that RRSIG, NSEC, and NSEC3 records are omitted from
the output.
- -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).
- -C
- This option indicates that named should check
consistency, meaning that 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.
- -d
- This option prints debugging traces, and is equivalent to
the -v verbose option.
- -l
- This option tells named to list the zone, meaning
the host command performs a zone transfer of zone name and
prints out the NS, PTR, and address records (A/AAAA).
Together, the -l -a options print all records in the
zone.
- -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.
- -p port
- This option specifies the port to query on the server. The
default is 53.
- -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 -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 can be referrals to other name
servers.
- -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.
- -s
- This option tells 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.
- -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, host automatically selects an
appropriate query type. By default, it looks for A, AAAA, and MX records.
If the -C option is given, queries are made for SOA records. If
name is a dotted-decimal IPv4 address or colon-delimited IPv6
address, 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., -t IXFR=12345678.
- -T, -U
- This option specifies TCP or UDP. By default, host
uses UDP when making queries; the -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 -U.
- -m flag
- This option sets memory usage debugging: the flag can be
record, usage, or trace. The -m option can be
specified more than once to set multiple flags.
- -v
- This option sets verbose output, and is equivalent to the
-d debug option. Verbose output can also be enabled by setting the
debug option in /etc/resolv.conf.
- -V
- This option prints the version number and exits.
- -w
- This option sets "wait forever": the query
timeout is set to the maximum possible. See also the -W
option.
- -W wait
- This options sets the length of the wait timeout,
indicating that 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, 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 -w option.
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 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
host runs.
/etc/resolv.conf
dig(1),
named(8).
Internet Systems Consortium
2024, Internet Systems Consortium