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?

Thanks

Ken