Guenther Grau <Guenther.Grau@bk.bosch.de> typed:
:Heiko W.Rupp wrote:
:> Geoff Wing wrote:
:> |Of course, union mounting isn't stable, so don't have more than one task doing
:> |anything in there.
:> What exactly is not stable in there? You mean changing files in /usr/src
:> and in the mount above at the same time? Or other things?
:the union filesystem is known to be unstable. It still contains quite
:a few bugs. I would be really great if someone actually tried to get
:it fixed, but it seems noone bothered so far.

However, from what I've seen, you can happily use it if only one process is
writing to the union; more than one can be reading from it.  I always build
my kernel and binaries with a union-mounting of /usr/obj over /usr/src and
haven't had real problems with that over the last couple of years, except 
for the above mentioned, and a couple of other mount idiosyncrasies - IIRC,
1) don't have the mount point as a symbolic link if you intend to unmount it
   (without rebooting your system - I think that not even a call to unmount(2)
   did it but I'm not quite sure about that - it's been a while)
2) mount it twice (which I've done by mistake a few times) and you'll be
   pressing that reset button - actually, I think you can issue a
   reboot/shutdown command, but again, it's been a while.

Once you know what sort of stuff to avoid, it's really very handy.
-- 
Geoff Wing   <gcw@pobox.com>            Mobile : 0412 162 441
Work URL: http://www.primenet.com.au/   Ego URL: http://pobox.com/~gcw/