os Parameter
------------
(type=string, default to compiled in value). Same as the `-O'
option to Amd. Allows you to override the compiled-in name of the
operating system. Useful when the built-in name is not desired for
backward compatibility reasons. For example, if the built-in name is
`sunos5', you can override it to `sos5', and use older maps which were
written with the latter in mind.