[Unionfs] UnionFS as root filesystem

[Torsten Luettgert]

On Mi, 2006-03-15 at 09:53 -0500, Francesco Carsana wrote:
> Tomas M wrote:
> > This way:
> >
> > mount /dev/hda1 /mnt/hda1
> > mount /dev/hda2 /mnt/hda2
> > mount -o dirs=/mnt/hda1=rw:/mnt/hda2=ro unionfs /mnt/union
> > chroot /mnt/union # or whatever you need to use, eg. cd /mnt/union; 
> > exec sbin/init <dev/console >dev/console
> 
> I have to use pivot_root... or not? Only chroot?
> So in my linuxrc:
> 
>    mount -o dirs=/mnt/hda1=ro:/mnt/hda2=rw unionfs /mnt/hda2
> 
> is wrong? Can't I mount the union over hda2?

If you can avoid it, don't. Granted, I have seen it work, but it's
always cleaner to have the fans separated from the union.

I did have problems with pivot_root, though. They fixed some
link count issue or whatever, and newer Kernels (at least new 2.6ers)
always return EINVAL if you pivot_root from an initrd.

The new way to do this seems to be mount --move. I wrote this to the
list a while ago, too, I think there's a bit more detail in that
post.

Hth,
Torsten