View Source: hostname(7) - Waikato Linux Users Group

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__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'' subdomain
of the ``EDU'' sub- domain of the Internet Domain
Name System would be repre- sented 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 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 pro- cessing.


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 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 this will be the only domain
appended to the partial hostname. For exam- ple, 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 meth- ods. 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 speci- fied); 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.
__ENVIRONMENT__
       LOCALDOMAIN
Affects domains appended to partial host- names.


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 !DistributionFebruary 16, 1994 1
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Last edited on Monday, June 3, 2002 11:58:28 pm by "perry"
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