Automatic fsck behavior

Automatic fsck behavior

[Daniel]

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?

2) If it's a real fsck, is it done in repair mode or diagnostic mode?

Also, do the answers depend/vary according to ext4 version or anything else?

Thank you

Re: Automatic fsck behavior

[Eric Sandeen]

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.

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
*) 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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Re: Automatic fsck behavior

[Andreas Dilger]

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On Jul 16, 2014, at 9:14 PM, Eric Sandeen <sandeen@redhat.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
>> 
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>> 
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html


Cheers, Andreas






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Re: Automatic fsck behavior

[Daniel]

Ok, got it.

Thank you both very much for your help - it's greatly appreciated.