Dump questions

[Jerry McAllister]

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
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