HOST(1) BSD Reference Manual
HOST(1)
NAME
host - look up host names using domain server
SYNOPSIS
host [-l] [-v] [-w] [-r] [-d] [-t querytype] [-a] host
[server]
DESCRIPTION
Host looks for information about Internet hosts. It gets
this informa-
tion 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 main-
tained by the do-
main 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 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 Rut-
gers 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 suf-
fix to tack on
the end is obtained by looking at the results of a host-
name(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 differ-
ent 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.RUT-
GERS.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.RUT-
GERS.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. Technical-
ly, every sys-
tem 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 men-
tion 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. Sys-
tems on
Usenet, Bitnet, and a number of other networks have entries
of this kind.
OPTIONS
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 main-
tain 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 do-
main 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).
-t querytype
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 in-
clude: ``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'', ex-
cept that if the verbose option is turned on,
the default is
only ``a''. The ``-t'' option is particularly
useful for fil-
tering information returned by host; see the ex-
planation 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 rut-
gers.edu domain.
The ``-t'' option is used to filter what infor-
mation is pre-
sented, as you would expect. The default is ad-
dress informa-
tion, 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 rut-
gers.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
necessary.
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 speci-
fy 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.
ENVIRONMENT
HOSTALIASES Name of file containing (host alias,
full hostname)
pairs.
FILES
/etc/resolv.conf See resolver(5).
SEE ALSO
named(8), resolver(5).
BUGS
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 do-
main 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
works.
4th Berkeley Distribution December 15, 1994
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