HP-UX Reference (11i v1 00/12) - 5 Miscellaneous Topics, 7 Device (Special) Files, 9 General Information, Index (vol 9)

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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 usuallyperformed by the library routine gethostbyname(3N).)

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 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 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 host-

name 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 (regard-

less 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

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.