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HOST
Section: BIND9 (1)Updated: 2009-01-20
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NAME
host - DNS lookup utilitySYNOPSIS
- host [-aCdlnrsTUwv] [-c class] [-N ndots] [-R number] [-t type] [-W wait] [-m flag] [[-4] | [-6]] [-v] [-V] {name} [server]
DESCRIPTION
host
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.
OPTIONS
-4
- Use IPv4 only for query transport. See also the -6 option.
-6
- Use IPv6 only for query transport. See also the -4 option.
-a
- "All". The -a option is normally equivalent to -v -t ANY. It also affects the behaviour of the -l list zone option.
-c class
- Query class: This can be used to lookup HS (Hesiod) or CH (Chaosnet) class resource records. The default class is IN (Internet).
-C
- Check consistency: host will query 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
- Print debugging traces. Equivalent to the -v verbose option.
-i
- Obsolete. Use the IP6.INT domain for reverse lookups of IPv6 addresses as defined in RFC1886 and deprecated in RFC4159. The default is to use IP6.ARPA as specified in RFC3596.
-l
-
List zone: 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
- 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.
-r
- Non-recursive query: Setting this option clears the RD (recursion desired) bit in the query. 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 can be referrals to other name servers.
-R number
- Number of retries for UDP queries: If number is negative or zero, the number of retries will default to 1. The default value is 1, or the value of the attempts option in /etc/resolv.conf, if set.
-s
- Do not 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
-
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 will be made for SOA records. 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 (like -t IXFR=12345678).
-T, -U
- TCP/UDP: 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. Type ANY queries default to TCP but can be forced to UDP initially using -U.
-m flag
- Memory usage debugging: the flag can be record, usage, or trace. You can specify the -m option more than once to set multiple flags.
-v
- Verbose output. Equivalent to the -d debug option. Verbose output can also be enabled by setting the debug option in /etc/resolv.conf.
-V
- Print the version number and exit.
-w
- Wait forever: The query timeout is set to the maximum possible. See also the -W option.
-W wait
-
Timeout: Wait for up to
wait
seconds for a reply. If
wait
is less than one, the wait interval is set to one second.
By default, host will wait 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.
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
SEE ALSO
AUTHOR
Internet Systems Consortium, Inc.
COPYRIGHT
Copyright © 2000-2002, 2004, 2005, 2007-2009, 2014-2017 Internet Systems Consortium, Inc. ("ISC")
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HOST.CONF
Section: Linux System Administration (5)Updated: 2017-09-15
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NAME
host.conf - resolver configuration fileDESCRIPTION
The file /etc/host.conf contains configuration information specific to the resolver library. It should contain one configuration keyword per line, followed by appropriate configuration information. The following keywords are recognized:- trim
- This keyword may be listed more than once. Each time it should be followed by a list of domains, separated by colons (':'), semicolons (';') or commas (','), with the leading dot. When set, the resolver library will automatically trim the given domain name from the end of any hostname resolved via DNS. This is intended for use with local hosts and domains. (Related note: trim will not affect hostnames gathered via NIS or the hosts(5) file. Care should be taken to ensure that the first hostname for each entry in the hosts file is fully qualified or unqualified, as appropriate for the local installation.)
- multi
- Valid values are on and off. If set to on, the resolver library will return all valid addresses for a host that appears in the /etc/hosts file, instead of only the first. This is off by default, as it may cause a substantial performance loss at sites with large hosts files.
- reorder
- Valid values are on and off. If set to on, the resolver library will attempt to reorder host addresses so that local addresses (i.e., on the same subnet) are listed first when a gethostbyname(3) is performed. Reordering is done for all lookup methods. The default value is off.
ENVIRONMENT
The following environment variables can be used to allow users to override the behavior which is configured in /etc/host.conf:- RESOLV_HOST_CONF
- If set, this variable points to a file that should be read instead of /etc/host.conf.
- RESOLV_MULTI
- Overrides the multi command.
- RESOLV_REORDER
- Overrides the reorder command.
- RESOLV_ADD_TRIM_DOMAINS
- A list of domains, separated by colons (':'), semicolons (';') or commas (','), with the leading dot, which will be added to the list of domains that should be trimmed.
- RESOLV_OVERRIDE_TRIM_DOMAINS
- A list of domains, separated by colons (':'), semicolons (';') or commas (','), with the leading dot, which will replace the list of domains that should be trimmed. Overrides the trim command.
FILES
- /etc/host.conf
- Resolver configuration file
- /etc/resolv.conf
- Resolver configuration file
- /etc/hosts
- Local hosts database
NOTES
The following differences exist compared to the original implementation. A new command spoof and a new environment variable RESOLV_SPOOF_CHECK can take arguments like off, nowarn, and warn. Line comments can appear anywhere and not only at the beginning of a line.Historical
The nsswitch.conf(5) file is the modern way of controlling the order of host lookups.In glibc 2.4 and earlier, the following keyword is recognized:
- order
- This keyword specifies how host lookups are to be performed. It should be followed by one or more lookup methods, separated by commas. Valid methods are bind, hosts, and nis.
- RESOLV_SERV_ORDER
- Overrides the order command.
Since glibc 2.0.7, the following keywords and environment variable have been recognized but never implemented:
- nospoof
- Valid values are on and off. If set to on, the resolver library will attempt to prevent hostname spoofing to enhance the security of rlogin and rsh. It works as follows: after performing a host address lookup, the resolver library will perform a hostname lookup for that address. If the two hostnames do not match, the query fails. The default value is off.
- spoofalert
- Valid values are on and off. If this option is set to on and the nospoof option is also set, the resolver library will log a warning of the error via the syslog facility. The default value is off.
- spoof
- Valid values are off, nowarn, and warn. If this option is set to off, spoofed addresses are permitted and no warnings will be emitted via the syslog facility. If this option is set to warn, the resolver library will attempt to prevent hostname spoofing to enhance the security and log a warning of the error via the syslog facility. If this option is set to nowarn, the resolver library will attempt to prevent hostname spoofing to enhance the security but not emit warnings via the syslog facility. Setting this option to anything else is equal to setting it to nowarn.
- RESOLV_SPOOF_CHECK
- Overrides the nospoof, spoofalert, and spoof commands in the same way as the spoof command is parsed. Valid values are off, nowarn, and warn.
SEE ALSO
gethostbyname(3), hosts(5), nsswitch.conf(5), resolv.conf(5), hostname(7), named(8)COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
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