On Wed, May 10, 2017 at 11:54:50AM +0200, Ruediger Meier wrote:
> I wonder why wipefs does not show all MBR and GPT signatures which would
> be deleted by using "-fa".
>
> $ truncate -s 100M /tmp/CCC
> $ ./sfdisk /tmp/CCC <<EOF
> > label: gpt
> > label-id: 384A8F14-17FF-4782-A190-A5B858E3FCF0
> > device: /tmp/CCC
> > unit: sectors
> > first-lba: 34
> > last-lba: 204766
> > EOF
>
> $ ./wipefs -fa --no-act /tmp/CCC
> /tmp/CCC: 8 bytes were erased at offset 0x00000200 (gpt): 45 46 49 20 50
> 41 52 54
>
> $ ./wipefs -fa /tmp/CCC
> /tmp/CCC: 8 bytes were erased at offset 0x00000200 (gpt): 45 46 49 20 50
> 41 52 54
> /tmp/CCC: 8 bytes were erased at offset 0x063ffe00 (gpt): 45 46 49 20 50
> 41 52 54
> /tmp/CCC: 2 bytes were erased at offset 0x000001fe (PMBR): 55 aa
This is not a bug, man wipefs:
Note that some filesystems and some partition tables store more magic
strings on the device. The wipefs command lists only the first
offset where a magic string has been detected. The device is
not scanned for additional magic strings for the same filesystem. It
is possible that after a wipefs -o offset the same filesystem or
partition table will still be visible because of another magic string
on another offset.
The "-a" writes zeros, resets the scanner and repeat scan again and
again until nothing is found. I will add note about it to the man
page...
It would be probably possible to extend libblkid to work in some
"ignore previous result" mode to to gather all permutation for the
FS/RAID/etc, but it won't be trivial task...
Karel
--
Karel Zak <kzak@xxxxxxxxxx>
http://karelzak.blogspot.com
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