Date: Tue, 23 Feb 2010 13:12:03 -0500 From: Jerry McAllister <jerrymc@msu.edu> To: Matthew Seaman <m.seaman@infracaninophile.co.uk> Cc: Jerry McAllister <jerrymc@msu.edu>, Aiza <aiza21@comclark.com>, freebsd-questions <questions@freebsd.org> Subject: Re: Dump questions Message-ID: <20100223181203.GB49549@gizmo.acns.msu.edu> In-Reply-To: <4B829E49.3050202@infracaninophile.co.uk> References: <4B80ABBA.9000707@comclark.com> <20100221110358.9ec8b286.freebsd@edvax.de> <20100222030127.GA41439@gizmo.acns.msu.edu> <4B8206AE.8080105@comclark.com> <20100222143028.GA43687@gizmo.acns.msu.edu> <4B829E49.3050202@infracaninophile.co.uk>
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On Mon, Feb 22, 2010 at 03:10:01PM +0000, Matthew Seaman wrote:
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> On 22/02/2010 14:30, Jerry McAllister wrote:
> > No. In multi-user, files are still changing. The snapshot could
> > possibly be made between parts of a change - between different writes
> > to the file, so there could be some inconsistency. In practice this
> > is not a big problem, but, single user with filesystems unmounted is
> > still the most absolute way of making sure a filesystem is quiescent
> > during a dump.
>
> Umm.... you don't *need* to go to single user to ensure a consistent
> filesystem dump: unmounting the partition is sufficient, or remounting
> it read-only.
True. But, the problem with that, as you follow with is that it can
produce a lot of fudd from parts of the running system that expect to
find that file system mountable and writable. Plus some filesystems
such as maybe /usr, etc may be needed for the multi-user system to
operate at all. So, you either don't dump them or go to single user
just for them or use -L and not worry about it, or whatever.
////jerry
> It's just that shutting the system down and rebooting to
> single user mode can save you a deal of faffing about trying to kill
> off any processes still using the filesystem, which would otherwise
> block your ability to unmount it.
>
> Note too, it's *reboot* into single user ('shutdown -r now', then press
> 4 at the boot menu) not *drop* into single user ('shutdown now') which
> doesn't unmount filesystems for you, although it should kill almost all
> processes.
>
> Single user has it's own disadvantages: generally there's no network
> configured, and with the root partition mounted read-only, you can't
> update /etc/dumpdates.
>
> Whenever you boot into single user, remember to run 'fsck -p' to ensure
> filesystem integrity. I'm not sure what happens if you attempt to
> dump'n'restore a dirty filesystem, but it's certainly going to have
> unintended consequences if the filesystem is actually damaged rather
> than just dirty.
>
> Cheers,
>
> Matthew
>
> - --
> Dr Matthew J Seaman MA, D.Phil. 7 Priory Courtyard
> Flat 3
> PGP: http://www.infracaninophile.co.uk/pgpkey Ramsgate
> Kent, CT11 9PW
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