Ext4 file system corruption and possible data loss

[Markus Schönhaber]

19.01.2010 19:18, Ari Torhamo:

> Thanks Markus for your reply. The problem with this non-booting Ubuntu
> 9.10 system has turned out to be serious. I connected the hard disk it's
> installed on to my own computer to test it, and found out that both ext4
> partitions on the disk are more or less unreadable. Gnome disk utility
> says that the /home partition is "unknown or unused" and it also isn't
> visible in Nautilus. The system partition is shown as "Linux ext4
> (version 1.0)", but the content cannot be read (the lost+found folder is
> there, but I'm not able to set the permission to myself - and there's no
> user data on that partition anyway).
> 
> I ran "fsck.ext4 -pfv" for both partitions (I'm not familiar with this
> tool, so I may have done something wrong), and I got the following
> results.

I wouldn't have run fsck on the file-systems on the disk but created
images of the file-systems via dd first and operated on those.

[...]
> System partition:
> 
> .............................
> 
> ari at mung-papu:~$ sudo fsck.ext4 -pfv /dev/sdb6
> 
>       11 inodes used (0.00%)
>        0 non-contiguous files (0.0%)
>        0 non-contiguous directories (0.0%)
>          # of inodes with ind/dind/tind blocks: 0/0/0
>          Extent depth histogram: 1
>    99190 blocks used (2.71%)
>        0 bad blocks
>        1 large file
> 
>        0 regular files
>        2 directories
>        0 character device files
>        0 block device files
>        0 fifos
>        0 links
>        0 symbolic links (0 fast symbolic links)
>        0 sockets
> --------
>        2 files

Whatever trashed the disk, it seems it did a good job...

> When I tried to re-install Ubuntu to the problematic system partition,
> the following error message was shown right after the installation
> started:
> 
> "Failed to remove conflicting files
> The installer needs to remove operating system files from the install
> target, but was unable to do so. The install cannot continue."
>
> I also tried to remove and recreate the system partition before
> installing, but got the same error message anyway. 

Which is to be expected. Deleting and re-creating the partition didn't
change it's content.
Make sure that the installer formats the partition, i. e. creates a new
file-system from scratch (or do that manually before you start the
installation).

> I run a thorough test for the hard disk, and no errors were found.
> Complete run of Memtest showed no errors either (in the computer that
> the hard disk belongs to). The Windows installation on the disk works
> without problems.

Nevertheless, I'd check the drive's SMART status before I'd trust it
with any data. Palimpsest can show SMART data - if you like a GUI.
Moreover, the problem might be caused by a corrupted partition table.
You could use something like testdisk to see if it finds the start of
file-systems at places where they shouldn't be according to the
partition table.
Oh, before you do anything else, backup the Windows partition.

> What might be the next step to try to get the /home partition readable?

Well, I'm out of ideas. But you might want to browse through this thread
of the linux-ext4 mailing list:
http://markmail.org/message/3w5tbyaiho7os4fr

> It's been more than a month since the user did the last back-up, so some
> data will be lost, if there's no success. Of course it would be
> important to know what lead to this situation too, as the reliability of
> the operating system (using the word in the broad meaning) might be in
> question.

Indeed, that would be important to know.
Although something may have gone wrong during the installation of the
updates, I doubt that it's Ubuntu's fault. If there really was a bug in
the update process, it almost certainly would have hit more than just
one machine - and we would have heard the outcry.
And since the canonical answer to the question "What did you do when
that happened?" of a user who has just fubar'ed his system is
"Absolutely nothing!!!", I don't see much chance to get much information
from the user.

-- 
Regards
  mks