hostname

NAME

       hostname - host name resolution description

DESCRIPTION

       Hostnames  are  domains.  A domain is a hierarchical, dot-
       separated list of subdomains.  For  example,  the  machine
       monet,  in  the Berkeley subdomain 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
       programs,  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 administrator to override these  recommen-
       dations  and  to have the resolver behave the same as ear-
       lier, 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 hostname.  The file should con-
       sist 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-insensitive 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 configurable by setting the threshold using  the
       ``ndots'' option in /etc/resolv.conf (default: 1).  If the
       name ends with a dot, the trailing dot is removed, and the
       remaining  name is looked up (regardless of the setting of
       the 'ndots' option) and no further processing is done.

       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 ``LOCALDOMAIN'' environment
       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.Berkeley.EDU,  then  only
       CS.Berkeley.EDU will be in the search list and will be the
       only domain appended to the partial hostname, for example,
       ``lithium'',  making lithium.CS.Berkeley.EDU the only name
       to be tried using the search list.

       If the search option is used in  /etc/resolv.conf  or  the
       environment  variable, ``LOCALDOMAIN'' is set by the user,
       then the search list will include what  is  set  by  these
       methods. For example, if the ``search'' option contained
            CS.Berkeley.EDU CChem.Berkeley.EDU Berkeley.EDU
       then  the  partial  hostname  (e.g.,  ``lithium'') will be
       tried with each domainname appended  (in  the  same  order
       specified).   The  resulting 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 originally provided is attempted.

SEE ALSO

       gethostbyname(3), resolver(5), mailaddr(7), named(8)