host

HOST(1)                     General Commands 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
     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(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 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 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.

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
     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.

     -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 include: “a”, “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
                 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 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.

ENVIRONMENT
     HOSTALIASES         Name of file containing (host alias, full hostname)
                         pairs.

FILES
     /etc/resolv.conf    See resolver(5).

     HOSTALIASES         Name of file containing (host alias, full hostname)
                         pairs.

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
     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 works.

4th Berkeley Distribution      December 15, 1994     4th Berkeley Distribution