linux-ext4 - Re: Automatic fsck behavior

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Message-Id: <2C9CD996-D4E0-44EE-9907-0986A02D2296@dilger.ca>
Date:	Wed, 16 Jul 2014 21:41:12 -0600
From:	Andreas Dilger <adilger@...ger.ca>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Daniel <dnlfrm@...unepc.com>, linux-ext4@...r.kernel.org
Subject: Re: Automatic fsck behavior

On Jul 16, 2014, at 9:14 PM, Eric Sandeen <sandeen@...hat.com> wrote:
> On 7/16/14, 9:55 PM, Daniel wrote:
>> Hi,
>> 
>> Had some questions about automatic boot-time fsck, following a power-loss or
>> hard-shutdown, etc.
>> All prior research (web searching, etc) on this has been inconclusive.
>> 
>> 1) Does it do a real fsck or only a journal playback?
> 
> By default, e2fsck at boot time only replays the journal if
> needed.

To elaborate a bit further - e2fsck will always do a sanity check of
the superblock when it is opening the filesystem to replay the journal.

> A full fsck at boot time is generally only done if:
> 
> *) The filesystem was marked with an error prior to the fsck due
>   to a runtime metadata error

or if the error was stored in the journal, even if it couldn't be
written to the superblock.

Cheers, Andreas

> *) Mount-count or time-based thresholds have been reached
>   (newer mke2fs doesn't set these threshold by default)
> 
>> 2) If it's a real fsck, is it done in repair mode or diagnostic mode?
> 
> Depends on how initscripts invoke it, but most likely
> it is in preen ("repair the easy stuff") mode.
> 
>> Also, do the answers depend/vary according to ext4 version or anything else?
> 
> yep, see above, w.r.t. initscript behavior, older/newer mke2fs,
> e2fsck.conf, mke2fs.conf, etc ;)
> 
> -Eric
> 
> 
>> Thank you
>> 
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> 
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Cheers, Andreas






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