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Date:   Thu, 21 Nov 2019 13:22:40 -0500
From:   "Theodore Y. Ts'o" <>
To:     "Darrick J. Wong" <>
Cc:     linux-ext4 <>,
Subject: Re: [PATCH] tune2fs: prohibit toggling uninit_bg on live filesystems

On Wed, Nov 20, 2019 at 11:32:55AM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <>
> An internal customer followed an erroneous AskUbuntu article[1] to try to
> change the UUID of a live ext4 filesystem.  The article claims that you
> can work around tune2fs' "cannot change UUID on live fs" error by
> disabling uninit_bg, changing the UUID, and re-enabling the feature.
> This led to metadata corruption because tune2fs' journal descriptor
> rewrite races with regular filesystem writes.  Therefore, prevent
> administrators from turning on or off uninit_bg on a mounted fs.
> [1]
> Signed-off-by: Darrick J. Wong <>

Thanks, applied.

					- Ted

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