host.1

早期freebsd实现

.TH host 1 "930926"
.SH NAME
host \- query nameserver about domain names and zones
.SH SYNOPSIS 
.na
.nf
\fBhost\fP [\fB\-v\fP] [\fB\-a\fP] [\fB\-t\fP \fIquerytype\fP] [\fIoptions\fP]  \fIname\fP  [\fIserver\fP] 
.br
\fBhost\fP [\fB\-v\fP] [\fB\-a\fP] [\fB\-t\fP \fIquerytype\fP] [\fIoptions\fP]  \fB\-l\fP \fIzone\fP  [\fIserver\fP] 
.br
\fBhost\fP [\fB\-v\fP] [\fIoptions\fP]  \fB\-H\fP [\fB\-D\fP] [\fB\-E\fP] [\fB\-G\fP] \fIzone\fP
.br
\fBhost\fP [\fB\-v\fP] [\fIoptions\fP]  \fB\-C\fP \fIzone\fP
.br
\fBhost\fP [\fB\-v\fP] [\fIoptions\fP]  \fB\-A\fP \fIhost\fP
.sp
\fBhost\fP [\fIoptions\fP] \fB\-x\fP  [\fIname\fP ...]
.br
\fBhost\fP [\fIoptions\fP] \fB\-X\fP \fIserver\fP  [\fIname\fP ...]
.SH DESCRIPTION 
.I host
looks for information about Internet hosts and domain names.
It gets this information from a set of interconnected servers
that are spread across the world. The information is stored
in the form of "resource records" belonging to hierarchically
organized "zones".
.PP
By default, the program simply converts between host names and Internet
addresses. However, with the \fB\-t\fP, \fB\-a\fP and \fB\-v\fP
options, it can be used to find all of the information about
domain names that is maintained by the domain nameserver system.
The information printed consists of various fields of the
associated resource records that were retrieved.
.PP
The arguments can be either host names (domain names) or numeric
Internet addresses.
.PP
A numeric Internet address consists of four decimal numbers
separated by dots, e.g. \fB192.16.199.1\fP, representing the
four bytes of the 32-bit address.
.br
The default action is to look up the associated host name.
.PP
A host name or domain name consists of component names (labels)
separated by dots, e.g. \fBnikhefh.nikhef.nl\fP
.br
The default action is to look up all of its Internet addresses.
.PP
For single names without a trailing dot, the local domain is
automatically tacked on the end.
Thus a user in domain "nikhef.nl" can say "host nikhapo",
and it will actually look up "nikhapo.nikhef.nl".
In all other cases, the name is tried unchanged.
Single names with trailing dot are considered top-level domain
specifications, e.g. "nl."
.PP
Note that the usual lookup convention for any name that does not end
with a trailing dot is to try first with the local domain appended,
and possibly other search domains.
This convention is not used by this program.
.PP
The actual suffix to tack on the end is usually the local domain
as specified in the \fB/etc/resolv.conf\fP file, but this can be
overridden.
See below for a description of how to customize the host name lookup.
.SH ARGUMENTS
The first argument is normally the host name (domain name) for which
you want to look up the requested information.
If the first argument is an Internet address, a query is done on the
special "reversed mapping" domain to look up its associated host name.
.PP
If the \fB\-l\fP option is given, the first argument is a domain zone
name for which a complete listing is given. The program enters a
special zone listing mode which has several variants (see below).
.PP
The second argument is optional. It allows you to specify a particular
server to query.  If you don't specify this argument, default servers
are used, as defined by the \fB/etc/resolv.conf\fP file.
.SH EXTENDED SYNTAX
If the \fB\-x\fP option is given, it extends the syntax in the sense
that multiple arguments are allowed on the command line. An optional
explicit server must now be specified using the \fB\-X\fP option as it
cannot be given as an ordinary argument any more. The \fB\-X\fP
option implies \fB\-x\fP.
.sp
The extended syntax allows no arguments at all, in which case the
arguments will be read from standard input. This can be a pipe,
redirection from a file, or an interactive terminal. Note that
these arguments are the names to be queried, and not command options.
Everything that appears after a '#' or ';' on an input line will be
skipped. Multiple arguments per line are allowed.
.SH OPTIONS
There are a number of options that can be used before the specified
arguments.  Some of these options are meaningful only to the people
who maintain the domain database zones.
The first options are the regularly used ones.
.TP 4
.B \-v
causes printout to be in a "verbose" format.
All resource record fields are printed.
Without this option, the TTL and class fields are not shown.
Also the contents of the "additional information" and "authoritative
nameservers" sections in the answer from the nameserver are printed,
if present.  Normally these sections are not shown.
In addition, the verbose option prints extra information about the
various actions that are taken by the program.
Note that \fB\-vv\fP is "very verbose". This generates a lot of output.
.TP
.BI \-t " querytype"
allows you to specify a particular type of resource record information
to be looked up.  Supported types are listed below.
The wildcard may be written as either \fBANY\fP or \fB*\fP.
Types may be given in upper or lower case.
The default is type \fBA\fP for regular lookups,
and \fBA\fP, \fBNS\fP, and \fBPTR\fP for zone listings.
.TP
.B \-a
is equivalent to \fB\-t ANY\fP.
Note that this gives you "anything available" (currently cached) and
not "all defined data" if a non-authoritative server is queried.
.SH SPECIAL MODES
The following options put the program in a special mode.
.TP 4
.BI \-l " zone"
generates the listing of an entire zone.
.sp
E.g. the command
.br
	\fBhost \-l nikhef.nl\fP
.br
will give a listing of all hosts in the "nikhef.nl" zone.
The \fB\-t\fP option is used to filter what information is
extracted, as you would expect. The default is address
information from A records, supplemented with data from PTR
and NS records.
.sp
The command
.br
	\fBhost \-v \-a \-l nikhef.nl\fP
.br
will give a complete download of the zone data for "nikhef.nl",
in the official master file format.
.TP 4
.B \-H
can be specified instead of the \fB\-l\fP option. It will print
the count of the unique hostnames (names with an A record)
encountered within the zone.
It will not count pseudo names like "localhost", nor addresses
associated with zone name itself. Neither are counted the
"glue records" that are necessary to define nameservers for
the zone and its delegated zones.
.sp
By default, this option will not print any resource records.
.sp
Combined with the \fB\-S\fP option, it will give a complete
statistics survey of the zone.
.sp
The host count may be affected by duplicate hosts (see below).
To compute the most realistic value, subtract the duplicate
host count from the total host count.
.TP
.B \-G
implies \fB\-H\fP, but lists the names of gateway hosts.
These are the hosts that have more than one address.
Gateway hosts are not checked for duplicate addresses.
.TP
.B \-E
implies \fB\-H\fP, but lists the names of extrazone hosts.
An extrazone host in zone "foo.bar" is of the form
"host.xxx.foo.bar" where "xxx.foo.bar" is not defined as
a delegated zone with an NS record.
This may be intentional, but also may be an error.
.TP
.B \-D
implies \fB\-H\fP, but lists the names of duplicate hosts.
These are hosts with only one address, which is known to
have been defined also for another host with a different name,
possibly even in a different zone.
This may be intentional, but also may be an error.
.TP
.B \-C
can be specified instead of the \fB\-l\fP option. It causes the SOA
records for the specified zone to be compared as found at each of
the authoritative nameservers for the zone (as listed in the NS records).
Nameserver recursion is turned off, and it will be checked whether
the answers are really authoritative. If a server cannot provide an
authoritative SOA record, a lame delegation of the zone to that server
is reported.
Discrepancies between the records are reported. Various sanity checks
are performed.
.TP
.B \-A
enters a special address check mode.
.sp
If the first argument is a host name, its addresses will be retrieved,
and for each of the addresses it will be checked whether they map back
to the given host.
.sp
If the first argument is a dotted quad Internet address, its name will
be retrieved, and it will be checked whether the given address is listed
among the known addresses belonging to that host.
.SH SPECIAL OPTIONS
The following options apply only to the special zone listing modes.
.TP 4
.BI \-L " level"
Recursively generate zone listings up to this level deep.
Level 1 traverses the parent zone and all of its delegated zones.
Each additional level descends into another layer of delegated zones.
.TP
.B \-S
prints statistics about the various types of resource records found
during zone listings, the number of various host classifications,
the number of delegated zones, and some total statistics after
recursive listings.
.TP
.B \-p
causes only the primary nameserver of a zone to be contacted for zone
transfers during zone listings. Normally, zone transfers are obtained
from any one of the authoritative servers that responds.  Note that
a specific server given on the command line overrules this option.
The primary nameserver is obtained from the SOA record of the zone.
.SH COMMON OPTIONS
The following options can be used in both normal mode and domain
listing mode.
.TP 4
.B \-T
prints the time-to-live values during non-verbose output.
By default the TTL is shown only in verbose mode.
It also prints the preference value for MX records.
.TP
.B \-d
turns on debugging.  Nameserver transactions are shown in detail.
Note that \fB\-dd\fP prints even more debugging output.
.TP
.B \-e
excludes information about names that are not residing within
the given zone during zone listings, such as some glue records.
For regular queries, it suppresses the printing of the "additional
information" and "authoritative nameserver" sections in the answer
from the nameserver.
.TP
.BI \-f " filename"
writes the resource record output to the given logfile as well as
to standard output.
.TP
.BI \-F " filename"
same as \fB\-f\fP, but exchange the role of stdout and logfile.
All stdout output goes to the logfile, and stdout gets only the
extra resource record output (so that it can be used in pipes).
This option is supported on a few platforms only.
.TP
.B \-i
constructs a query for the "reversed mapping" \fBin-addr.arpa\fP
domain in case a numeric (dotted quad) address was specified.
Useful primarily for zone listing mode, since for numeric regular
lookups such query is done anyway (but with \-i you see the actual