hostname(5)                     TCP/IP 5.4.2                     hostname(5)


NAME
       hostname - hostname resolution description

DESCRIPTION
       Hostnames are expressed as domain names, where a domain name is a
       hierarchical, dot-separated list of labels; for example, the machine
       abc, in the de subdomain of the COM subdomain would be represented as
       abc.de.COM (with no trailing dot).

       A label consists of up to 24 characters drawn from the lowercase
       alphabet (a-z), uppercase alphabet (A-Z), digits (0-9), and minus
       sign (-).  You cannot include blank or space characters in a label.
       No distinction is made between upper and lower case.

       Hostnames are often used with network client and server programs,
       which must generally translate the name to an address for use.  (This
       translation is generally performed by the library routine
       gethostbyname(3N).)  Hostnames are resolved by the domain name
       resolver in the following way.

       If the hostname consists of a single component, that is, 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 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-sensitive 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 the input hostname ends with a trailing dot, the trailing dot is
       removed, and the remaining hostname is looked up with no further
       processing.  A hostname that ends with a trailing dot is called a
       "fully-qualified" hostname.

       If the input hostname does not end with a trailing dot, it is looked
       up in the local domain and its parent domains until either a match is
       found or fewer than two components of the local domain remain.  For
       example, in the domain tnt.acme.COM, the name spectre.bucky will be
       checked first as spectre.bucky.tnt.acme.COM, then as
       spectre.bucky.acme.COM, then as spectre.bucky.COM, and then as
       spectre.bucky.

       If you use the Domain Name System (DNS) you must either 1) set the
       default domain in resolv.conf(4) and use hostnames that consist of a
       single component or 2) consistently use fully-qualified hostnames.

SEE ALSO
       named(1M), gethostbyname(3N), resolv.conf(4), RFC883.








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