Mount on top of / ??

[Bill Sconce]

   ...

> >  To issue a command of 'umount /' is going to confuse the kernel.


Just to clarify (and I apologize that I used sloppy wording which
didn't make this clear):  it wasn't "/" which I tried to unmount,
but the second device-special.  I.e., the sequence was


    # mount -t iso9660 /dev/hdc /

    # umount /dev/hdc
    
    <device is busy>
    
Thanks to all for the comments so far.  It's a help to have company
in thinking that this is a dark corner of Linux behavior, if nothing
else.

-Bill