this post was submitted on 27 Nov 2023
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FOUND file in device by hex content using wxHexEditor (lemmy.nz)
submitted 11 months ago* (last edited 11 months ago) by luthis@lemmy.nz to c/linux@lemmy.ml
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Just having a play around, this turned out to be not as clear cut as expected.

so I created a file and entered some text, used xxd to get the hex values, and then opened the device /dev/sdb1 in wxhexeditor and tried to find my file, but it's not finding it. Inode is 19, so it should be right at the start of the first block group, but after several minutes, no joy. (drive is ext4.)

I thought this was going to be an easy task, just multiply the inode by the block size, open the device with wxhexeditor, and scroll to the line corresponding to the calculated byte, copy out the hex values and convert to ascii and voila, there's the 'hello world'... except no.

What am I missing here? Drive isn't encrypted, nothing silly like that.

Ok, I managed to do it with dd:

sudo dd if=/dev/sdb1 bs=8M skip=$((4660742*4096)) iflag=skip_bytes | head -c 4096

hello

but why can I not find it using wxhexeditor??

EDIT:

Duh, I didn't click that offset needed to be multiplied by the block size.

If I go to offset 4660742*4096=19090399232 in wxhexeditor, indeed I see the file contents:

Final conclusion:

After some more testing, I have concluded: you cannot easily calculate the offset using the inode. Finding files across the disk requires using the inode tables to get the offset and actual file location. So an inode does not correlate with a physical/logical sequential disk location.

I created a new file, it received inode 21, but the offset was smaller than inode 19.

Was that a good use of 3 hours of my life? Well... I still have no idea what's up with the Kardashians, so.. I guess?

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[–] chunkyhairball@lemmy.ml 11 points 11 months ago (1 children)

Luthis, you're doing God's work here. You are learning by experimentation and then, importantly, documenting and sharing what you've learned. There is absolutely zero wrong and only good to be had in either of those and in combining them, you're doing service to our entire community.

[–] luthis@lemmy.nz 1 points 11 months ago

Thanks! I will keep it up!

[–] mvirts@lemmy.world 6 points 11 months ago

Sounds like a good time to me!! Hey and look at all that wasted space you found 😹

[–] SaltyIceteaMaker@lemmy.ml 5 points 11 months ago (1 children)

Of course that was worth 3 hours. Every tinkering/experimenting is worth it. In the worst case you gain experience

[–] luthis@lemmy.nz 3 points 11 months ago

Yeah now I stand a better chance of recovering files if something catastrophic happens

[–] Azzk1kr@feddit.nl 5 points 11 months ago (1 children)

You wasted three hours so you can share this knowledge :D

[–] luthis@lemmy.nz 3 points 11 months ago

True, now you have the power to find your files manually!

[–] luthis@lemmy.nz 3 points 11 months ago* (last edited 11 months ago)

Tried a different way:

 filefrag -v testfile 
Filesystem type is: ef53
File size of testfile is 6 (1 block of 4096 bytes)
 ext:     logical_offset:        physical_offset: length:   expected: flags:
   0:        0..       0:    4660742..   4660742:      1:             last,eof

Went to offset 4660742 in wxhexeditor, but still when I copy out the hex and convert to ascii, it's nonsense