[Pkg-sysvinit-devel] Bug#670106: initscripts: please ignore noauto sysfs entries in fstab

[Carsten Hey]

* Roger Leigh [2012-04-24 16:31 +0100]:
> On Tue, Apr 24, 2012 at 02:55:55PM +0200, Michael Prokop wrote:
> > * Carsten Hey [Mon Apr 23, 2012 at 01:07:17 +0200]:
> >
> > > Please ignore noauto sysfs entries in fstab.  Not mounting sysfs to /sys
> > > if such a line is present in fstab leads to udev not starting.
> >
> > > If this bug is not fixed, this problems will show up after upgrading to
> > > Wheezy on some systems.
> > [...]
> >
> > FTR: According to my tests, bootstrapping wheezy with
> > grml-debootstrap 0.49 fails WRT /sys mounting and bootstrapping
> > whezzy with grml-debootstrap 0.50 (just released and uploaded, it
> > does not add a noauto sysfs line any longer) succeeds.
>
> So does this problem still need addressing in initscripts?

The problem is that installing Squeeze via grml-debootstrap perfectly
works and after upgrading to Wheezy udev will not start.  A wrongly
generated /etc/fstab can't be fixed for existing systems by releasing
a fixed version of a tool that is only run once during installation.


> We could certainly make it skip the noauto check for critical
> mountpoints like /proc and /sys.

I would prefer this.  An alternative to this would be commenting out
such lines in initscripts preinst, but as I already wrote, I would
prefer your suggestion to skip the noauto check for critical mountpoints
like /proc and /sys.


> OTOH, if you explicitly asked for that behaviour... we are only
> respecting the wishes of the admin.

initscripts is currently respecting what you obviously *think* are the
wishes of the admin.  Since /sys is nowadays mounted on most or all
major Linux distributions regardless of a possibly existing according
fstab entry and admins might know this, the wish of an admin who adds
such a noauto entry could also be "let me mount sysfs by only typing
'mount /sys' if I need to do a chroot", which I consider to be way more
likely than "don't mount /sys at all".  If some people would like
mounting /sys to be skipped, you should have received an according bug
report in all those years when this was not possible, i.e., before the
according change in initscripts that happend during Wheezy's release
cycle.


An argument to also expect such a noauto sysfs entry on systems not
installed via grml-debootstrap is (besides those webforum entries Google
finds) that the paper "The sysfs Filesystem" [1] published at the Linux
Symposium 2005 in Ottawa includes an fstab example entry for sysfs that
contains the option noauto.

I'm not sure if this entry was copied from a distribution or if the
paper is the first occurrence of such a line.  Anyway, one could expect
that using a sysfs paper published by a Linux kernel developer on
a major Linux conference as reference for a simple sysfs fstab entry
would be a good choice.

 [1] www.kernel.org/pub/linux/kernel/people/mochel/doc/papers/ols-2005/mochel.pdf


In my opinion, the underlying problem is that there is no clear and
distribution independent semantic of noauto when used in a fstab entry
for those standard virtual file systems.  If there would be such a clear
semantic, then either initscripts in Squeeze or the one in Wheezy would
be buggy as one of them wouldn't respect this clear semantic.


Regards
Carsten