[Ubuntu-users] fsck shows errors on main partition only when mounted

[K. Frank]

Hello Mark -

Thank you for your explanations.

On Tue, Nov 16, 2010 at 2:53 PM, Mark <mhullrich at gmail.com> wrote:
> On Tue, Nov 16, 2010 at 9:03 AM, K. Frank <kfrank29.c at gmail.com> wrote:
>> Hi Mark and Colin -
>>
>> Does this mean that even in "read-only" mode (-n) fsck assumes,
>> in effect, that the partition is not mounted, and therefore errors it
>> reports can be false positives?
>
> No, it means that fsck won't act on errors it thinks it finds.
> ...
>> So I was hoping to be able to check (safely) for errors by running fsck -n,
>> even though the file system was mounted.  Doing so showed errors, so
>> I ran fsck again with the file system unmounted, and (to my surprise) it
>> showed no errors.
>>
> It's sort of a "who ya gonna believe?"  A live volume is inherently
> more difficult to check for errors and since the data can change
> underneath a check as it is occurring, you can get things that look to
> fsck like errors but are not.
>
>> Hence my original question:  Are the errors that fsck -n showed on my
>> mounted file system false positives -- not really errors, but rather just
>> artifacts of the file system being mounted?  Or are they a problem I
>> should be worrying about (even though they don't show up when the
>> system is not mounted)?
>>
> "Data on it changes frequently" means that fsck cannot be relied upon
> to identify disk errors accurately because it depends on static data
> that won't change while it is reading to verify the contents..
>
> Answers in order from your last paragraph above: yes no (especially
> when they don't show up when the system is not mounted).
>
> Is that better?

Yes, thank you.  That helps clear up a number of things.

K. Frank