host -- look up host names using domain server
host [-l] [-v] [-w] [-r] [-d] [-t querytype] [-a] host [server]
Host looks for information about Internet hosts. It gets this information
from a set of interconnected servers that are spread across the
world. 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
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 IPv4 dotted decimal
quad (127.0.0.1) or IPv6 raw address (::1). 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
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(1) call, and
using everything starting at the first dot. (See below for a description
of CUSTOMIZING HOST NAME LOOKUP.)
The first argument is the host name you want to look up. If this is a
number, an ``inverse query'' is done, i.e. the domain system looks in a
separate set of databases used to convert numbers to names.
The second argument is optional. It allows you to specify a particular
server to query. If you don't 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 22.214.171.124
ATHOS.RUTGERS.EDU has address 126.96.36.199
ATHOS.RUTGERS.EDU mail is handled by ARAMIS.RUTGERS.EDU
The user has typed 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.
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.
-w This causes host to wait forever for a response. Normally it
will time out after approximate one minute.
-v Use "verbose" format for printout. This is the official
domain master file format, which is documented in the man
page for named(8). 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'',
any "a", "mx", and "cname" records are written out as "has
address", "mail is handled by", and "is a nickname for"
(respectively), and TTL and class fields are not shown.
-r Turn off recursion 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 Turn on debugging. Network transactions are shown in detail.
-s Chase signatures back to parent key (DNSSEC).
Allows you to specify a particular querytype of information
to be looked up. The arguments are defined in the man page
for named(8). Currently-supported types include: ``a'',
``aaaa'', ``ns'', ``md'', ``mf'', ``cname'', ``soa'', ``mb'',
``mg'', ``mr'', ``null'', ``wks'', ``ptr'', ``hinfo'',
``minfo'', ``mx'', ``uinfo'', ``uid'', ``gid'', ``unspec''.
Additionally, the wildcard, which may be written as either
``any'' or ``*'', can be used to specify any (all) of the
above types. 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''. The ``-t'' option is particularly useful for
filtering information returned by host; see the explanation
of the ``-l'' option, below, for more information.
-a ``all''; this is equivalent to ``-v -t any''.
-l List a complete domain; e.g.:
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 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: ``-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
CUSTOMIZING HOST NAME LOOKUP [Toc] [Back]
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. The name file must
be contained in the HOSTALIASES environment variable.
HOSTALIASES Name of file containing (host alias, full hostname)
/etc/resolv.conf See resolver(5).
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'' option 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
4th Berkeley Distribution December 15, 1994 4th Berkeley Distribution
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