Assume /usr/local is on a separate FFS partition.

I want to upgrade a freesoftware by overwriting the existing
files, but I am not sure if the new version works well.  So
I decide to test it by using union filesystem on /usr/local.

> # mkdir /tmp/local
> # mount -t union /tmp/local /usr/local
> # make install
> (do tests)

After testing, I may want to unmount /tmp/local.

> # umount -g /usr/local
> /dev/sd0g: unmount from /usr/local
> umount: /usr/local: Device busy

umount command is obviously going to unmount the `original'
/usr/local (lower directory).  Then I try

> # umount -v /tmp/local
> umount: /tmp/local: not currently mounted

It seems to consider /tmp/local as a mount point.

The question is: How can I unmount /tmp/local from /usr/local?

Thanks.

-- 
MINOURA, Makoto <minoura@kw.netlaputa.ne.jp> or <minoura@kyogoku.com>
Nakahara-ku Kawasaki-Shi, JAPAN