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Re: Stuff from /bin, /sbin, /lib depending on /usr/lib libraries

Hi Matthew,

On Sat, Sep 01, 2012 at 07:25:09PM +0100, Matthew Woodcraft wrote:
> Wouter Verhelst wrote:
> > Since you're talking of software RAID and LVM, that means you need an
> > initramfs to boot your system. Thus, your systems will continue to
> > boot with the proposed scenario, which supports booting with /usr on a
> > separate filesystem if you have an initramfs.

> Using software RAID and LVM does not require an initramfs.

> Debian has supported booting from md RAID without using an initramfs for
> a very long time.

True but misleading.  LILO supported it because it hard-coded the block list
of the kernel and initrd at install time.  GRUB1 never supported any RAID
except for RAID1, as far as I'm aware.  GRUB2 has supported RAID5 since
~2008, but has only been used as the default boot loader in Debian since
2011; prior to that the installer would select the best bootloader for the
chosen disk layout - but grub2 was sufficiently experimental at that point
that no one who actually cared about their data would be using it.

As for LVM, I'm not aware of any implementation that supports kernel
auto-activation of VGs without an initramfs.

> GRUB2 can boot from LVM or a separate /boot, but in any case risk-averse
> people might choose to avoid root-on-LVM; this is one of the reasons for
> putting /usr on a separate filesystem in the first place.

I wouldn't call this being risk averse, I would call it being *bad* at risk
assessment / risk management.  All the interesting data needed for running
the system is on a filesystem other than the root filesystem in that case.
If you actually think LVM isn't safe, you shouldn't be using it for /usr
(and /var).  If you think it is safe, you should have / on it as well and,
if necessary, allocate a separate /boot partition for the bootloader.

> The system I'm sending this email from would fail to boot if separate
> /usr without initramfs stops being supported.

Can you please elaborate on why that is?  Is there something in your
configuration that would prevent an initramfs from being automatically used
by the bootloader when generated at kernel install time?  Are there
particular constraints on your environment that would prevent the system
from using an initramfs if one was required (e.g., would there be some
reason you would have to reinstall to adapt to such new requirements)?

> If Debian doesn't want to continue doing the work to support that
> configuration, fair enough; I'll change.  But I'd like to correct the
> impression that such systems don't exist.

My assertion isn't that an initramfsless system with /usr as a separate
filesystem can't be done; my assertion is, rather, than it is an
uninteresting configuration to support and that dropping support for it
won't negatively impact our users.  If I'm mistaken about this, I'd
certainly like to know it.

Steve Langasek                   Give me a lever long enough and a Free OS
Debian Developer                   to set it on, and I can move the world.
Ubuntu Developer                                    http://www.debian.org/
slangasek@ubuntu.com                                     vorlon@debian.org

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