HOSTNAME(7)                        BSD      Reference      Manual
HOSTNAME(7)

NAME
     hostname - host name resolution description

DESCRIPTION
     Hostnames are domains.  A domain is a hierarchical, dot-sep-
arated list of
     subdomains.   For  example,  the  machine  ``monet'', in the
``Berkeley'' sub-
     domain of the ``EDU'' subdomain of the Internet Domain  Name
System would
     be represented as

           monet.Berkeley.EDU

     (with no trailing dot).

     Hostnames are often used with network client and server pro-
grams, which
     must generally translate the name to  an  address  for  use.
(This task is
     usually  performed by the library routine gethostbyname(3).)
The default
     method for resolving hostnames by the Internet name resolver
is to follow
     RFC  1535's  security recommendations.  Actions can be taken
by the admin-
     istrator to override these recommendations and to  have  the
resolver be-
     have the same as earlier, non-RFC 1535 resolvers.

     The default method (using RFC 1535 guidelines) follows:

     If the name consists of a single component, i.e. contains no
dot, and if
     the environment variable ``HOSTALIASES'' is set to the  name
of a file,
     that  file is searched for a string matching the input host-
name.  The file
     should consist of lines made up of two strings separated  by
white-space,
     the  first of which is the hostname alias, and the second of
which is the
     complete hostname to be substituted for that  alias.   If  a
case-insensi-
     tive  match is found between the hostname to be resolved and
the first
     field of a line in the file, the substituted name is  looked
up with no
     further processing.

     If  there  is at least one dot in the name, then the name is
first tried
     ``as-is''. The number of dots to cause this action  is  con-
figurable by
     setting   the   threshold  using  the  ``ndots''  option  in
/etc/resolv.conf (de-
     fault:  1).  If the name ends with a dot, the  trailing  dot
is removed,
     and  the remaining name is looked up (regardless of the set-
ting of the
     ndots option), without further processing.

     If the input name does not end with a trailing  dot,  it  is
looked up by
     searching  through a list of domains until a match is found.
If neither
     the search option in the /etc/resolv.conf file or the  ``LO-
CALDOMAIN'' en-
     vironment  variable is used, then the search list of domains
contains only
     the  full  domain  specified  by  the  domain   option   (in
/etc/resolv.conf) or
     the  domain  used in the local hostname (see hostname(1) and
resolver(5)).
     For example, if the ``domain'' option is  set  to  CS.Berke-
ley.EDU, then on-
     ly CS.Berkeley.EDU will be in the search list, and this will
be the only
     domain appended to the partial hostname.   For  example,  if
``lithium'' is
     the  name  to be resolved, this would make lithium.CS.Berke-
ley.EDU the only
     name to be tried using the search list.

     If the search option is used in /etc/resolv.conf or the  en-
vironment vari-
     able  ``LOCALDOMAIN''  is  set  by the user, then the search
list will in-
     clude what is set by these methods.   For  example,  if  the
``search'' op-
     tion contained

           CS.Berkeley.EDU CChem.Berkeley.EDU Berkeley.EDU

     then  the partial hostname (e.g., ``lithium'') will be tried
with each do-
     main name appended (in the same order  specified);  the  re-
sulting hostnames
     that would be tried are:

           lithium.CS.Berkeley.EDU
           lithium.CChem.Berkeley.EDU
           lithium.Berkeley.EDU

     The   environment  variable  ``LOCALDOMAIN''  overrides  the
``search'' and
     ``domain'' options, and if both search  and  domain  options
are present in
     the  resolver  configuration  file,  then  only the last one
listed is used
     (see resolver(5)).

     If the name was not previously  tried  ``as-is''  (i.e.,  it
fell below the
     ``ndots'' threshold or did not contain a dot), then the name
as original-
     ly provided is attempted.

ENVIRONMENT
     LOCALDOMAIN          Affects  domains  appended  to  partial
hostnames.

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

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

SEE ALSO
     gethostbyname(3),  resolver(5),  mailaddr(7),  named(8).

4th    Berkeley    Distribution         February     16,     1994
2