HOSTNAME(7)					       BSD Miscellaneous Information Manual					       HOSTNAME(7)

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 recommendations and to have the
     resolver behave 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 hostname.  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-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), 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 nei-
     ther the search option in the /etc/resolv.conf file or the ``LOCALDOMAIN'' environment variable is used, then the search list of domains con-
     tains only the full domain specified by the domain option (in /etc/resolv.conf) or the domain used in the local hostname.	For example, if
     the ``domain'' option is set to CS.Berkeley.EDU, then only 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.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 domain name appended (in the same order specified); the resulting host-
     names 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 orig-
     inally 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 resolver(5).

SEE ALSO

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

BSD
								 February 16, 1994							       BSD