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Re: How to fsck read-only-mounted root filesystem?

To: Dan Hollis <goemon@xxxxxxxxx>
Subject: Re: How to fsck read-only-mounted root filesystem?
From: Steve Lord <lord@xxxxxxx>
Date: 05 Dec 2001 16:28:36 -0600
Cc: Simon Matter <simon.matter@xxxxxxxxxxxxxxxx>, linux xfs ml <linux-xfs@xxxxxxxxxxx>
In-reply-to: <Pine.LNX.4.30.0112051325360.6782-100000@xxxxxxxxx>
References: <Pine.LNX.4.30.0112051325360.6782-100000@xxxxxxxxx>
Sender: owner-linux-xfs@xxxxxxxxxxx
On Wed, 2001-12-05 at 15:40, Dan Hollis wrote:
> On Wed, 5 Dec 2001, Simon Matter wrote:
> > Dan Hollis schrieb:
> > > How can one xfs_check/xfs_repair a root filesystem?
> > Boot from a bootable CD and perform the repair on the unmounted
> > filesystem.
> > Have a look at this http://lbt.linuxcare.com/index.epl
> 
> Seems a bit ridiculous to have to install a CDrom just to fsck the root
> filesystem.

No, it is just that the environment xfs comes from (Irix) tends to
use other mechanisms to fix root filesystems - like an alternate
root, or a miniroot.

It is also not 'install a cdrom', it is boot with a bootable cdrom.

Doing a user space fixup of a live filesystem also relies upon the
block device cache and the filesystem's cache of metadata being
coherent. If they are not then this approach does not work and can
lead to nasty crashes very quickly. XFS was until recently using
completely different caches for metadata than the block interface,
they now use the same memory - mostly. Until they are coherent
there is absolutely no point in doing modifications to a mounted
XFS fs from user space.


> 
> After all, reiserfs can reiserfsck a filesystem mounted read-only...
> 
> Maybe it's a bug in xfs_check/xfs_repair?

   It is deliberate.

Steve

> 
> -Dan
> -- 
> [-] Omae no subete no kichi wa ore no mono da. [-]
-- 

Steve Lord                                      voice: +1-651-683-3511
Principal Engineer, Filesystem Software         email: lord@xxxxxxx


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