I wanted to create a "private /sys" directory with union mounts. I
get "union: Operation not supported"
  The location of the "upper" file system (the mount point with -b) is
on an NFS mount, specifically, an AMD managed mount. Is this a problem?
  Both NFS cliend and server are:

NetBSD amaterasu 1.2B NetBSD 1.2B (AMATERASU) #12: Sun Nov 24 01:42:02 EST 1996     mcr@a
materasu:/w/netbsd/src/sys/arch/sun3/compile/AMATERASU sun3

  It works just fine if the upper layer is a local file system.
  (Yes, I'm about to recompile current, but I have to do the
appropriate make/share/config/etc. rebuild on this machine)

   :!mcr!:            |  Network security consulting and 
   Michael Richardson |      contract programming
 WWW: mcr@sandelman.ottawa.on.ca. PGP key available.