On Thu, 8 Sep 2011 15:13:55 -0400, Canek Peláez Valdés wrote about Re:
[gentoo-user] /dev/sda* missing at boot:

> On Thu, Sep 8, 2011 at 2:05 PM, David W Noon <dwnoon@ntlworld.com>
> wrote:
[snip]
> > I don't know if the kernel offers any particular blessing to any
> > hotplug handler.
> 
> udev is the device manager for the Linux kernel. It replaced devfs.

One can use mdev just as readily as udev.

> It's related, but doesn't (necessarily) need to be the same that the
> user space part.
> 
> Yeah, udev is mandatory in the kernel, unless you use a traditional
> /dev directory.

But udev isn't actually part of the kernel.  Only hotplug support is
actually in the kernel.  The udev daemon is started during the sysinit
run-level and it connects itself to hotplug support.

[snip]
> >> Dracut automatizes this. Is a non-problem.
> >
> > If dracut actually worked ...
> 
> What doesn't work for you?

Since dracut is not yet stable, I don't have any problems with it
because I don't use it.  But it does have quite a few open bugs in
Gentoo's Bugzilla, and I suspect many more in other distro's bug
trackers.

> > During the "do stuff" phase, /usr is also writeable, which is
> > undesirable on production systems.  That's the *original* problem
> > with merging a read-only /usr with /. [We seem to be going in
> > circles with this one.]
> 
> It's the same when you upgrade the system. If you don't allow rw in
> /user *ever*, then you are not allowed to upgrade. Which I was chewed
> up because I said it was an alternative.

Production systems have strictly scheduled change-control windows,
usually only once or twice a year.  Having to schedule database changes
to match application change-control would not be workable.  That is
why /etc cannot be mounted read-only and still have /usr secured as
read-only.  This brings us back to a requirement that / and /usr be
physically separate filesystems.

[snip]
> > I have about 6 or 7 backup jobs that run during the night and
> > parse /etc/mtab to see if they need to place a copy of the backup
> > onto an external medium.  These examine the mount options and don't
> > understand the non-standard options offered by Linux
> > in /proc/mounts.
> 
> Really? You cannot grep -v those options to another file and make the
> jobs read this other file?

I would use gawk rather than grep.  But since I have code that already
works, why should I need to develop a new script?

> In my experience that sounds like a problem with the jobs.

They work currently.

Moreover, my rootfs is not read-only.  It is not desirable to have the
rootfs mounted read-only because of this problem and the other
problems it causes.  But for production systems it is desirable for /usr
to be mounted read-only and only made writeable during a change-control
window.

[snip]
> > They already don't do that.
> 
> Well, then you already know what to do.

Indeed I do.
-- 
Regards,

Dave  [RLU #314465]
*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
dwnoon@ntlworld.com (David W Noon)
*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*