hostname.5 (2010 09)

h
hostname(5) hostname(5)
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 Sys-
tem 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()
.)
When NIS or the host table is being used for hostname resolution, the hostname is looked up without
modification. When DNS is used, the resolver may append domains to the hostname.
The default method for resolving hostnames by the Internet name resolver is to follow
RFC 1535’s secu-
rity 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 compliant 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
HOS-
TALIASES 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) 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 LOCAL-
DOMAIN 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
resolver (4)). 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, 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 domain name 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
options are present in the resolver configuration file, then only the last one listed is used (see resolver (4)).
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.
AUTHOR
hostname was developed by the University of California, Berkeley.
SEE ALSO
named(1M), gethostbyname(3N), gethostent(3N), resolver(4), RFC 1535.
HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1