> I'm sorry if this is a dumb question, but I keep getting this:

> [~]$ mount -t union -o -b /usr/src/sys $HOME/sys
> union: Operation not supported

> It's the same if root does this.  I have "options UNION" in my config
> file, of course.  My system is current as of June 20th.

> Is union fs supported at all, or am I missing something obvious?

Poking around with ktrace, plus some UTSLing, indicates that the
problem is almost certainly that $HOME/sys is on a filesystem that
doesn't support whiteouts.  The unionfs in NetBSD depends on having
whiteouts available in the upper layer.  (IMO this is a defect, but I'm
not sure what to do about it.  Keeping metadata in upper-layer files
would be nice, but it would mean that at least some files would not
appear in the underlying upper-layer filesystem under their "native"
names, which would also be a defect.  Someday I may try to invent a way
around this.)

Alternatively, you can mount read-only, in which case the union fs
doesn't care whether whiteouts are supported.  But given the mount
you're trying to perform, I suspect you want RW access.

					der Mouse

			    mouse@collatz.mcrcim.mcgill.edu