178 lines
8.1 KiB
Groff
178 lines
8.1 KiB
Groff
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HOST(1) Minix Programmer's Manual HOST(1)
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NAME
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host - look up host names using domain server
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SYNOPSIS
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host [-l] [-v] [-w] [-r] [-d] [-t querytype] [-a] host [ server ]
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DESCRIPTION
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Host looks for information about Internet hosts. It gets this
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information from a set of interconnected servers that are spread across
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the 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 to
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find all of the information about this host that is maintained by the
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domain server.
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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, it will
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treat them as host names. A host number consists of first decimal
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numbers separated by dots, e.g. 128.6.4.194 A host name consists of names
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separated by dots, e.g. topaz.rutgers.edu. Unless the name ends in a dot,
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the local domain is automatically tacked on the end. Thus a Rutgers user
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can say "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"). This
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same convention is used for mail and other network utilities. The actual
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suffix to tack on the end is obtained by looking at the results of a
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"hostname" call, and using everything starting at the first dot. (See
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below for a description of how to customize the host name lookup.)
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The first argument is the host name you want to look up. If this is a
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number, an "inverse query" is done, i.e. the domain system looks in a
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separate set of databases used to convert numbers to names.
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The second argument is optional. It allows you to specify a particular
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server to query. If you don't specify this argument, the default server
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(normally the local machine) is used.
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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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% host sun4
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sun4.rutgers.edu is a nickname for ATHOS.RUTGERS.EDU
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ATHOS.RUTGERS.EDU has address 128.6.5.46
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ATHOS.RUTGERS.EDU has address 128.6.4.4
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ATHOS.RUTGERS.EDU mail is handled by ARAMIS.RUTGERS.EDU
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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 address.
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If a system has more than one network interface, there will be a separate
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address for each. The last line indicates that ATHOS.RUTGERS.EDU does
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not receive its own mail. Mail for it is taken by ARAMIS.RUTGERS.EDU.
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There may be more than one such line, since some systems have more than
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one other system that will handle mail for them. Technically, every
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1
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HOST(1) Minix Programmer's Manual HOST(1)
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system that can receive mail is supposed to have an entry of this kind.
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If the system receives its own mail, there should be an entry the
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mentions the system itself, for example "XXX mail is handled by XXX".
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However many systems that receive their own mail do not bother to mention
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that fact. If a system has a "mail is handled by" entry, but no address,
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this indicates that it is not really part of the Internet, but a system
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that is on the network will forward mail to it. Systems on Usenet,
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Bitnet, and a number of other networks have entries of this kind.
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There are a number of options that can be used before the host name.
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Most of these options are meaningful only to the staff who have to
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maintain the domain database.
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The option -w causes host to wait forever for a response. Normally it
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will time out after around a minute.
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The option -v causes printout to be in a "verbose" format. This is the
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official domain master file format, which is documented in the man page
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for "named". Without this option, output still follows this format in
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general terms, but some attempt is made to make it more intelligible to
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normal users. Without -v, "a", "mx", and "cname" records are written out
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as "has address", "mail is handled by", and "is a nickname for", and TTL
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and class fields are not shown.
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The option -r causes recursion to be turned off in the request. This
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means that the name server will return only data it has in its own
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database. It will not ask other servers for more information.
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The option -d turns on debugging. Network transactions are shown in
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detail.
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The option -t allows you to specify a particular type of information to
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be looked up. The arguments are defined in the man page for "named".
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Currently supported types are a, ns, md, mf, cname, soa, mb, mg, mr,
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null, wks, ptr, hinfo, minfo, mx, uinfo, uid, gid, unspec, and the
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wildcard, which may be written as either "any" or "*". Types must be
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given in lower case. Note that the default is to look first for "a", and
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then "mx", except that if the verbose option is turned on, the default is
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only "a".
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The option -a (for "all") is equivalent to "-v -t any".
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The option -l causes a listing of a complete domain. E.g.
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host -l rutgers.edu
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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 would
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expect. The default is address information, which also include PTR and
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NS records. The command
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host -l -v -t any rutgers.edu
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will give a complete download of the zone data for rutgers.edu, in the
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2
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HOST(1) Minix Programmer's Manual HOST(1)
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official master file format. (However the SOA record is listed twice,
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for arcane reasons.) NOTE: -l is implemented by doing a complete zone
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transfer and then filtering out the information the you have asked for.
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This command should be used only if it is absolutely necessary.
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CUSTOMIZING HOST NAME LOOKUP
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In general, if the name supplied by the user does not have any dots in
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it, a default domain is appended to the end. This domain can be defined
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in /etc/resolv.conf, but is normally derived by taking the local hostname
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after its first dot. The user can override this, and specify a different
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default domain, using the environment variable LOCALDOMAIN. In addition,
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the user can supply his own abbreviations for host names. They should be
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in a file consisting of one line per abbreviation. Each line contains an
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abbreviation, a space, and then the full host name. This file must be
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pointed to by an environment variable HOSTALIASES, which is the name of
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the file.
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See Also
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named (8)
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BUGS
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Unexpected effects can happen when you type a name that is not part of
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the local domain. Please always keep in mind the fact that the local
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domain name is tacked onto the end of every name, unless it ends in a
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dot. Only if this fails is the name used unchanged.
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The -l option only tries the first name server listed for the domain that
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you have requested. If this server is dead, you may need to specify a
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server manually. E.g. to get a listing of foo.edu, you could try "host -t
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ns foo.edu" to get a list of all the name servers for foo.edu, and then
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try "host -l foo.edu xxx" for all xxx on the list of name servers, until
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you find one that works.
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3
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