On Wednesday 10 May 2017, Karel Zak wrote: > 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. I see. > > 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... Thanks. For me it's a bit hard to guess what wipefs would actually do. I have another issue, using wipefs on the same image like above: $ ./wipefs -fa -t gpt /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: 8 bytes were erased at offset 0x063ffe00 (gpt): 45 46 49 20 50 41 52 54 There are two duplicated lines in the output and the not-mentioned (P)MBR is also removed. > 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... This would be nice. cu, RUdi -- To unsubscribe from this list: send the line "unsubscribe util-linux" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
