Is the upper layer a 4.4 filesystem?
	4.2 & 4.3 filesystems do not support whiteouts, which unionfs needs.
	(I got caught by this one :)

	good filesystem:

(neutron ~)255># dumpfs /dev/rsd0e | head -2
magic   11954   time    Fri Oct 20 13:34:33 1995
cylgrp  dynamic inodes  4.4BSD

	bad filesystem: (In union terms :)
	
(neutron ~)254># dumpfs /dev/rsd0a | head -2
magic   11954   time    Thu Oct 26 10:07:19 1995
cylgrp  dynamic inodes  4.2/4.3BSD

	You can 'fsck -c 2 device'  to upgrade a filesystem to 4.4.
	(But make sure you do not do this to a root filesystem if it
	needs to be 4.3/4.2 (ie a sparc using sunos boot blocks))

		David/abs

david@city.ac.uk +44 171 477 8186 (MIME) david@southern.com +44 0181 88 8949
Network Analyst, UCS, City University   System Manager, Southern Studios Ltd
Northampton Square, London EC1V 0HB                PO Box 59, London N22 1AR

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On Wed, 25 Oct 1995, Gary D. Duzan wrote:

> 
>    I just started to try the union fs so I may be missing the obvious,
> but it seems that mount_union only works read-only, which rather
> defeats the purpose:
> 
> wheel { /tmp } % ls foo bar
> bar:
> ack
> 
> foo:
> blah    xyzzy
> wheel { /tmp } % mount -t union foo bar
> union: Operation not supported
> wheel { /tmp } % mount -r -t union foo bar
> wheel { /tmp } % ls foo bar
> bar:
> ack     blah    xyzzy
> 
> foo:
> blah    xyzzy
> wheel { /tmp } % 
> 
>    I can do a null mount between another directory and the mount
> point to get write access, but that seems rather convoluted. Also,
> I noticed that if you leave a trailing / on the mount directory
> for a null fs mount then you can't umount it later because umount
> thinks it isn't mounted. Can anyone else recreate or explain this
> behavior? Thanks.
> 
>                                       Gary D. Duzan
>                          Humble Practitioner of the Computer Arts
> 
> 
>