208 lines
9.8 KiB
Groff
208 lines
9.8 KiB
Groff
.\" ++Copyright++ 1993
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.\" -
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.\" Copyright (c) 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\" -
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.\" Portions Copyright (c) 1993 by Digital Equipment Corporation.
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.\"
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.\" Permission to use, copy, modify, and distribute this software for any
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.\" purpose with or without fee is hereby granted, provided that the above
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.\" copyright notice and this permission notice appear in all copies, and that
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.\" the name of Digital Equipment Corporation not be used in advertising or
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.\" publicity pertaining to distribution of the document or software without
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.\" specific, written prior permission.
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.\"
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.\" THE SOFTWARE IS PROVIDED "AS IS" AND DIGITAL EQUIPMENT CORP. DISCLAIMS ALL
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.\" WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL DIGITAL EQUIPMENT
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.\" CORPORATION BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
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.\" DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
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.\" PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS
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.\" ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS
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.\" SOFTWARE.
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.\" -
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.\" --Copyright--
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.\" $Id: host.1,v 1.2 1994/09/22 21:52:02 pst Exp $
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.TH HOST 1
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.SH NAME
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host \- look up host names using domain server
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.SH SYNOPSIS
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host [-l] [-v] [-w] [-r] [-d] [-t querytype] [-a] host [ server ]
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.SH DESCRIPTION
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.I Host
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looks for information about Internet hosts. It gets this information
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from a set of interconnected servers that are spread across the
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country. By default, it simply converts between host names and
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Internet addresses. However with the -t or -a options, it can be used
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to find all of the information about this host that is maintained
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by the domain server.
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.PP
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The arguments can be either host names or host numbers. The program
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first attempts to interpret them as host numbers. If this fails,
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it will treat them as host names. A host number consists of
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first decimal numbers separated by dots, e.g. 128.6.4.194
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A host name
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consists of names separated by dots, e.g. topaz.rutgers.edu.
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Unless the name ends in a dot, the local domain
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is automatically tacked on the end. Thus a Rutgers user can say
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"host topaz", and it will actually look up "topaz.rutgers.edu".
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If this fails, the name is tried unchanged (in this case, "topaz").
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This same convention is used for mail and other network utilities.
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The actual suffix to tack on the end is obtained
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by looking at the results of a "hostname" call, and using everything
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starting at the first dot. (See below for a description of
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how to customize the host name lookup.)
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.PP
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The first argument is the host name you want to look up.
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If this is a number, an "inverse query" is done, i.e. the domain
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system looks in a separate set of databases used to convert numbers
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to names.
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.PP
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The second argument is optional. It
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allows you to specify a particular server to query. If you don't
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specify this argument, the default server (normally the local machine)
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is used.
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.PP
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If a name is specified, you may see output of three different kinds.
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Here is an example that shows all of them:
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.br
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% host sun4
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.br
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sun4.rutgers.edu is a nickname for ATHOS.RUTGERS.EDU
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.br
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ATHOS.RUTGERS.EDU has address 128.6.5.46
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.br
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ATHOS.RUTGERS.EDU has address 128.6.4.4
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.br
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ATHOS.RUTGERS.EDU mail is handled by ARAMIS.RUTGERS.EDU
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.br
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The user has typed the command "host sun4". The first line indicates
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that the name "sun4.rutgers.edu" is actually a nickname. The official
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host name is "ATHOS.RUTGERS.EDU'. The next two lines show the
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address. If a system has more than one network interface, there
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will be a separate address for each. The last line indicates
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that ATHOS.RUTGERS.EDU does not receive its own mail. Mail for
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it is taken by ARAMIS.RUTGERS.EDU. There may be more than one
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such line, since some systems have more than one other system
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that will handle mail for them. Technically, every system that
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can receive mail is supposed to have an entry of this kind. If
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the system receives its own mail, there should be an entry
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the mentions the system itself, for example
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"XXX mail is handled by XXX". However many systems that receive
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their own mail do not bother to mention that fact. If a system
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has a "mail is handled by" entry, but no address, this indicates
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that it is not really part of the Internet, but a system that is
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on the network will forward mail to it. Systems on Usenet, Bitnet,
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and a number of other networks have entries of this kind.
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.PP
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There are a number of options that can be used before the
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host name. Most of these options are meaningful only to the
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staff who have to maintain the domain database.
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.PP
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The option -w causes host to wait forever for a response. Normally
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it will time out after around a minute.
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.PP
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The option -v causes printout to be in a "verbose" format. This
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is the official domain master file format, which is documented
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in the man page for "named". Without this option, output still follows
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this format in general terms, but some attempt is made to make it
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more intelligible to normal users. Without -v,
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"a", "mx", and "cname" records
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are written out as "has address", "mail is handled by", and
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"is a nickname for", and TTL and class fields are not shown.
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.PP
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The option -r causes recursion to be turned off in the request.
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This means that the name server will return only data it has in
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its own database. It will not ask other servers for more
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information.
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.PP
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The option -d turns on debugging. Network transactions are shown
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in detail.
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.PP
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The option -t allows you to specify a particular type of information
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to be looked up. The arguments are defined in the man page for
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"named". Currently supported types are a, ns, md, mf, cname,
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soa, mb, mg, mr, null, wks, ptr, hinfo, minfo, mx, uinfo,
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uid, gid, unspec, and the wildcard, which may be written
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as either "any" or "*". Types must be given in lower case.
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Note that the default is to look first for "a", and then "mx", except
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that if the verbose option is turned on, the default is only "a".
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.PP
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The option -a (for "all") is equivalent to "-v -t any".
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.PP
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The option -l causes a listing of a complete domain. E.g.
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.br
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host -l rutgers.edu
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.br
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will give a listing of all hosts in the rutgers.edu domain. The -t
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option is used to filter what information is presented, as you
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would expect. The default is address information, which also
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include PTR and NS records. The command
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.br
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host -l -v -t any rutgers.edu
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.br
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will give a complete download of the zone data for rutgers.edu,
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in the official master file format. (However the SOA record is
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listed twice, for arcane reasons.) NOTE: -l is implemented by
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doing a complete zone transfer and then filtering out the information
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the you have asked for. This command should be used only if it
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is absolutely necessary.
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.SH CUSTOMIZING HOST NAME LOOKUP
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In general, if the name supplied by the user does not
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have any dots in it, a default domain is appended to the end.
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This domain can be defined in /etc/resolv.conf, but is normally derived
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by taking the local hostname after its first dot. The user can override
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this, and specify a different default domain, using the environment
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variable
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.IR LOCALDOMAIN .
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In addition, the user can supply his own abbreviations for host names.
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They should be in a file consisting of one line per abbreviation.
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Each line contains an abbreviation, a space, and then the full
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host name. This file must be pointed to by an environment variable
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.IR HOSTALIASES ,
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which is the name of the file.
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.SH "See Also"
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named (8)
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.SH BUGS
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Unexpected effects can happen when you type a name that is not
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part of the local domain. Please always keep in mind the
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fact that the local domain name is tacked onto the end of every
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name, unless it ends in a dot. Only if this fails is the name
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used unchanged.
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.PP
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The -l option only tries the first name server listed for the
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domain that you have requested. If this server is dead, you
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may need to specify a server manually. E.g. to get a listing
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of foo.edu, you could try "host -t ns foo.edu" to get a list
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of all the name servers for foo.edu, and then try "host -l foo.edu xxx"
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for all xxx on the list of name servers, until you find one that
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works.
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