Under Mac OS X, the hostname handling is unusual. The hostname that the
hostname command or the gethostname function return is
determined by the name set in the ``Sharing preference'' pane. If this name
contains a space, you may get only the leading part of the name, upto but not
including the first space. This name is stored in the file
/etc/hostconfig. MPICH, for the ch_p4 and
ch_p4mpd device, needs a sensible name returned by both
gethostname and hostname. If you are using a single machine
in a standalone configuration, the easiest option is to change the name of the
machine in /etc/hostconfig to localhost (use sudo).
If you wish to use
another name, you need to make the name in /etc/hostconfig match the
name in the NetInfo database.
Thanks to Victor Eijkhout for this information.