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Re: Is inability to operate with root read-only (and separate /etc, /dev, etc) a bug or design decision?


On Sat, Aug 12, 2006 at 09:34:52PM +0200, Goswin von Brederlow wrote:
> Peter Samuelson <peter@p12n.org> writes:
> > [Goswin von Brederlow]
> >> Instead move the things in etc that need writing to other places:
> >> 
> >> 1) link /etc/mtab to /proc/mounts and create a dummy /proc/mounts on /
> >>    for when /proc isn't mounted (works with quota in current kernels).
> >
> > Does the wrong thing with (a) user and (b) loop mounts.  [I just tested
> > 2.6.16-1-k7.]  /etc/mtab needs to keep enough state for umount to know
> > (a) who mounted something, so the same user can unmount it, and (b)
> > that a loop device was set up automatically via 'mount -o loop', rather
> > than done separately, so that umount can 'losetup -d /dev/loopN'.  This
> > is information which cannot, at present, be put in /proc/mounts.
> Yes. If you need that feature help patching the kernel (like the new
> quota support in /proc/mounts) or link it to somewhere else.

Which doesn't work because of linux-utils-2.12r/mount/fstab.c:55
mtab_is_writable() {
	static int ret = -1;

	/* Should we write to /etc/mtab upon an update?
	   Probably not if it is a symlink to /proc/mounts, since that
	   would create a file /proc/mounts in case the proc filesystem
	   is not mounted. */
	if (mtab_is_a_symlink())
		return 0;

The path to mtab is also hardcoded in
/usr/include/paths.h:54:#define _PATH_MOUNTED   "/etc/mtab"
which is no fun to change "on-the-fly".

Philipp Matthias Hahn <pmhahn@debian.org>
 GPG/PGP: 9A540E39 @ keyrings.debian.org

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