HOSTNAME(7) 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 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,
February 16, 1994 1
HOSTNAME(7) HOSTNAME(7)
``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)
February 16, 1994 2
Please look at the man2html translation issues.
man2html.pl Version 1.1, Copyright 1997, 1998 by Richard Dawe