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HOSTNAME(7)	   FreeBSD Miscellaneous Information Manual	   HOSTNAME(7)

     hostname -- host name resolution description

     Hostnames are domains.  A domain is a hierarchical, dot-separated list of
     subdomains.  For example, the machine "monet", in the "Berkeley" subdo-
     main of the "EDU" subdomain of the	Internet Domain	Name System would be
     represented as


     (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 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 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-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 configurable by set-
     ting 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 op-
     tion), 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 "LOCALDOMAIN" envi-
     ronment 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.  For example, if the "domain" op-
     tion 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 vari-
     able "LOCALDOMAIN"	is set by the user, then the search list will include
     what is set by these methods.  For	example, if the	"search" option	con-

	   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 resulting hostnames
     that would	be tried are:


     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.

     LOCALDOMAIN	 Affects domains appended to partial hostnames.

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

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

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

4th Berkeley Distribution      February	16, 1994     4th Berkeley Distribution


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