How to rescue your partitions after upgrade to Fedora 18 Alpha eats them

Sun Sep 23 16:09:17 UTC 2012

On 09/23/2012 07:33 AM, Jakub Kicinski wrote:
> Hi all,
>
> I recently had a weird problem after "upgrade" to Fedora 18 Alpha. I
> decided to share the solution, maybe it will help someone.
>
> But first:
>
> 1. The rant
>
> Clearly something bad is going on in Fedora world. I've been
> upgrading to Alphas/Betas for years now and it never caused more
> trouble than occasional need to rebuild some packages manually.
>
> I read this:
> http://lwn.net/Articles/506831/
> but I didn't suspect that not only Rawhide, but also Alpha releases
> became unusable.
>
> First of all PreUpgrade crashes before it starts. I thought, well, I'll
> try DVD. It kind of worked. I was looking for words like "upgrade" or
> "update" in the new and shiny anaconda but no luck. Eventually it
> started the installation (without any "Warning: write changes to
> disk?" or alike). At that point partitions of Fedora 17 where already
> magically renamed to Fedora 18, so I hoped for the best. Unfortunately
> anaconda crashed when it tried to format my Win7 partition to the
> widely used filesystem "None"?! Imagine my amusement when after reboot
> I realised that MBR and GPT where wiped out and all of my partitions
> were nowhere to be found.
>
> 2. The problem
>
> It turned out anaconda not only wipes out MBR but also removes magic
> numbers from partitions superblocks (anyone can explain why?). So the
> good news was my data was still there, the bad news was: none of
> automatic "lost partition detection" tool could find them (at least none
> that I know of).
>
> 3. The solution
>
> If it happens to you as well, here is what you can try to get your
> data back:
>
>   a. Accept that you do all this on your own risk ;)
>   b. Backup your HDD, preferably all of it. Backup can be done with dd.
>   c. Connect damaged HDD to some other Linux box or use a Live
>      distribution.
>   d. Now you need to locate your first partition. There is a good chance
>      that this will be your /boot and Fedora usually locates it at
>      0x100000 (i.e. it starts in 2048 sector). Other possibility is
>      sector 63/64 from pre-GPT world.
>   e. Set magic value in superblock (see below).
>   f. Try mounting partition using offset option in mount.
>   g. Calculate where next partition is most likely to start using block
>      count and block size from superblock.
>   h. Fix your MBR. You can probably do that in parted or some similar
>      tool, but who would trust tools after one just nearly destroyed all
>      your data.
>   i. If you have more partitions to find, go back to (d).
>
>
> Important: All values on disk are LITTLE ENDIAN.
> Important: Try mounting your partitions read-only first.
>
> Notes on EXT4.
> Ext4 is quite easy to find. You will recognize it by two zeroed out
> sectors (1024 bytes of zeroes) at the beginning of every partition.
> NOTE: those zeroes are *in* the partition, do not skip them when trying
> to mount. After zeroes there is a superblock. What you are looking
> for is offset +0x38 in the superblock, where you once had a magic value
> of 0xEF53, you will probably have to put it back there. More information
> on EXT4:
> https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout
>
> Notes on NTFS.
> NTFS partition starts with EB 52 90, there are no zeroes in front. Magic
> value which is removed by anaconda is "4E 54 46 53 20 20 20 20"
> at offset 0x03 into a partition. Its literally "NTFS    " (with spaces).
> More info:
> http://technet.microsoft.com/en-us/library/cc781134%28v=ws.10%29.aspx
>
> Useful tools:
> dd - will help you to copy blocks of data around. If you don't know it
> already, I advise you to read some tutorial and practise first. It's
> easy to destroy thing with one wrong dd.
>
> emacs, okteta etc. - hex editor...
>
> losetup - is a tool which enables you to mount files and drives at
> particular offset as loop devices. Very useful, read more here:
> http://rackerhacker.com/2010/12/14/mounting-a-raw-partition-file-made-with-dd-or-dd_rescue-in-linux/
>
> dumpe2fs, nftsinfo - will decode superblock for you.
>
> bash calculator - $((1+2+3+4*4)) can save you a lot of time.
> bash printf - printf "%d\n" 0x1AB2F or printf "%x\n" $((7863*4096)) is
> handy as well.
>
> Good luck from (a sightly less happy) Fedora user
>     -- Kuba
WOW!.....that's terrible! But I guess that's just one of the reasons I 
purposely wait until a release has been out for almost 3 
months....before installing / upgrading. It just makes it a little 
easier when the glitches have been made apparent and are either 
completely worked out or are in the process of being worked out. In all 
honesty...I actually prefer to wait a few releases before upgrading, I 
kind of have my OWN "schedule" I usually wait and let one release pass 
by, then I'll wait for the next version...and 3 to 4 months into _that 
_I'll upgrade.....this helps me remain a little more "stable" and not 
have to scurry around upgrading every 6 months....


EGO II
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