Subject: Re: What's up with union fs?
To: None <firstname.lastname@example.org>
From: der Mouse <mouse@Collatz.McRCIM.McGill.EDU>
Date: 06/27/1995 11:27:52
> 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?
Poking around with ktrace, plus some UTSLing, indicates that the
problem is almost certainly that $HOME/sys is on a filesystem that
doesn't support whiteouts. The unionfs in NetBSD depends on having
whiteouts available in the upper layer. (IMO this is a defect, but I'm
not sure what to do about it. Keeping metadata in upper-layer files
would be nice, but it would mean that at least some files would not
appear in the underlying upper-layer filesystem under their "native"
names, which would also be a defect. Someday I may try to invent a way
Alternatively, you can mount read-only, in which case the union fs
doesn't care whether whiteouts are supported. But given the mount
you're trying to perform, I suspect you want RW access.