host

Name

host — DNS lookup utility

Synopsis

host [-aCdlnrsTwv] [-c class] [-N ndots] [-R number] [-t type] [-W wait] [-m flag] [-4] [-6] {name} [server]

DESCRIPTION

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. 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 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 + 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 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 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 -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 recognized 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, AAAA, and MX 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 behavior. +

+ The -m can be used to set the memory usage debugging + flags + record, usage and + trace. +

IDN SUPPORT

+ 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 + 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 IDN_DISABLE environment variable. + The IDN support is disabled if the variable is set when + host runs. +

FILES

/etc/resolv.conf +

Name

Synopsis

DESCRIPTION

IDN SUPPORT

FILES

SEE ALSO