Now that I have made rarpd work, this question seems relevant.  rarpd
does not seem like it belongs in /usr/libexec, but rather /usr/sbin.
/usr/libexec is for programs which are invoked by other programs, and
which it does not make sense to run from the command line (such as
inet servers which expect their stdin/out to be a socket).

BTW, I added this to /etc/rc:

# $bootparam_server is imported from /etc/netstart;
# if $bootparam_server == YES, the machine is setup for being a rarp
# and bootparam server for diskless clients.
if [ "X${bootparam_server}" = X"YES" -a -d /tftpboot ]; then
	echo -n ' rarpd';		rarpd -a
	echo -n ' bootparamd';		bootparamd
fi

and put "bootparam_server=YES" in my /etc/netstart.  These changes
should be incorporated when my rarpd and bootparamd are.

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