Confused about fsck

Nils Kassube kassube at
Wed Dec 14 16:22:30 UTC 2011

Colin Law wrote:
> Every so often my system checks my disk on bootup.  I thought that
> this was done using fsck.  It takes a couple of minutes to do the
> check.

Yes, it is done by fsck.

> I have an external 250GB USB disk that I wish to check.  I plug in
> the disk and check it is not mounted (it appears as /dev/sdb1) and
> run sudo fsck /dev/sdb1
> This returns immediately saying that the disk is clean, whereas I had
> expected it to take a little while checking things, so it does not
> seem to be doing the same things that the check on startup does on
> the built in disk.  I can't see any options on fsck to specify what
> is to be checked.  Can someone explain what is going on?

Your external disk probably hasn't been mounted often enough to force a 
complete check. If it is a journalized file system like ext3/ext4, fsck 
only checks if there is something to correct from the journal. If you 
want to force a complete check anyway, you can use the -f option.


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