host(1) CLIX host(1)
NAME
host - Looks up host names using a domain server
SYNOPSIS
host [-l] [-v] [-w] [-r] [-d] [-t querytype] [-a] host [server]
FLAGS
There are a number of options that can be used before the host name. Most
of these options are meaningful only to the staff who have to maintain the
domain database.
-l Causes a listing of a complete domain. For example:
host -l rutgers.edu
will give a listing of all hosts in the rutgers.edu domain. The
-t option is used to filter what information is presented, as you
would expect. The default is address information, which also
include PTR and NS records. The following command:
host -l -v -t any rutgers.edu
will give a complete download of the zone data for rutgers.edu, in
the official master file format. (However the SOA record is
listed twice, for arcane reasons.) Note that -l is implemented by
doing a complete zone transfer and then filtering out the
information the you have asked for. This command should be used
only if it is absolutely necessary.
-v Causes printout to be in a verbose format. This is the official
domain master file format, which is documented in the named(8)
manpage. Without this option, output still follows this format in
general terms, but some attempt is made to make it more
intelligible to normal users. Without -v, a, mx, and cname records
are written out as "has address," "mail is handled by," and "is a
nickname for." Also, TTL and class fields are not shown.
-w Causes host to wait forever for a response. Normally it will time
out after around a minute.
-r Causes recursion to be turned off in the request. This means that
the name server will return only data it has in its own database.
It will not ask other servers for more information.
-d Turns on debugging. Network transactions are shown in detail.
-t querytype
Allows you to specify a particular type of information to be
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looked up. The arguments are defined in the named(8) manpage.
Currently supported types are a, ns, md, mf, cname, soa, mb, mg,
mr, null, wks, ptr, hinfo, minfo, mx, uinfo, uid, gid, unspec, and
the wildcard, which can be written as either any or *. Types must
be given in lower case. Note that the default is to look first
for a, and then mx, except that if the verbose option is turned
on, the default is only a.
-a ("all") Equivalent to -v -t any.
host Specifies the host name you want to look up. If this is a number,
an inverse query is done. For an inverse query, the domain system
looks in a separate set of databases used to convert numbers to
names.
server Allows you to specify a particular server to query. If you do not
specify this argument, the default server (normally the local
machine) is used.
If a name is specified, you may see output of three different
kinds. Here is an example that shows all of them:
$ host sun4
sun4.rutgers.edu is a nickname for ATHOS.RUTGERS.EDU
ATHOS.RUTGERS.EDU has address 128.6.5.46
ATHOS.RUTGERS.EDU has address 128.6.4.4
ATHOS.RUTGERS.EDU mail is handled by ARAMIS.RUTGERS.EDU
The user has keyed in the command host sun4. The first line
indicates that the name "sun4.rutgers.edu" is actually a nickname.
The official host name is "ATHOS.RUTGERS.EDU'. The next two lines
show the address. If a system has more than one network
interface, there will be a separate address for each. The last
line indicates that ATHOS.RUTGERS.EDU does not receive its own
mail. Mail for it is taken by ARAMIS.RUTGERS.EDU. There may be
more than one such line, since some systems have more than one
other system that will handle mail for them. Technically, every
system that can receive mail is supposed to have an entry of this
kind. If the system receives its own mail, there should be an
entry the mentions the system itself, for example "XXX mail is
handled by XXX". However many systems that receive their own mail
do not bother to mention that fact. If a system has a mail is
handled by entry, but no address, this indicates that it is not
really part of the Internet, but a system that is on the network
will forward mail to it. Systems on Usenet, Bitnet, and a number
of other networks have entries of this kind.
DESCRIPTION
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host(1) CLIX host(1)
The host command looks for information about Internet hosts. It gets this
information from a set of interconnected servers that are spread across
the country. By default, it simply converts between host names and
Internet addresses. However with the -t or -a options, it can be used to
find all of the information about this host that is maintained by the
domain server.
The arguments can be either host names or host numbers. The program first
attempts to interpret them as host numbers. If this fails, it will treat
them as host names. A host number consists of first decimal numbers
separated by dots, e.g. 128.6.4.194 A host name consists of names
separated by dots, e.g. topaz.rutgers.edu. Unless the name ends in a dot,
the local domain is automatically tacked on the end. Thus a Rutgers user
can say "host topaz", and it will actually look up "topaz.rutgers.edu".
If this fails, the name is tried unchanged (in this case, "topaz"). This
same convention is used for mail and other network utilities. The actual
suffix to tack on the end is obtained by looking at the results of a
"hostname" call, and using everything starting at the first dot. (See
below for a description of how to customize the host name lookup.)
CUSTOMIZING HOST NAME LOOKUP
In general, if the name supplied by the user does not have any dots in it,
a default domain is appended to the end. This domain can be defined in
/etc/resolv.conf, but is normally derived by taking the local hostname
after its first dot. The user can override this, and specify a different
default domain, using the environment variable LOCALDOMAIN. In addition,
the user can supply his own abbreviations for host names. They should be
in a file consisting of one line per abbreviation. Each line contains an
abbreviation, a space, and then the full host name. This file must be
pointed to by an environment variable HOSTALIASES, which is the name of
the file.
EXAMPLES
1. To see a complete listing of all hosts in a domain named rutgers.edu,
enter:
host -l rutgers.edu
2. To give a complete download of the zone data for rutgers.edu, in the
official master file format, enter:
host -l -v -t any rutgers.edu
FILES
/etc/resolv.conf
Domain Name System (DNS) client configuration file.
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NOTES
Unexpected effects can happen when you type a name that is not part of the
local domain. Please always keep in mind the fact that the local domain
name is tacked onto the end of every name, unless it ends in a dot. Only
if this fails is the name used unchanged.
The -l flag only tries the first name server listed for the domain that
you have requested. If this server is dead, you may need to specify a
server manually. E.g. to get a listing of foo.edu, you could try "host -t
ns foo.edu" to get a list of all the name servers for foo.edu, and then
try "host -l foo.edu xxx" for all xxx on the list of name servers, until
you find one that works.
RELATED INFORMATION
Commands: named(8)
Files: resolv.conf(4)
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