Mailinglist Archive: opensuse (1256 mails)

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Re: [opensuse] Wipe GPT partition table?
On 2017-05-08 15:45, Greg Freemyer wrote:
On Mon, May 8, 2017 at 7:42 AM, Ruediger Meier <sweet_f_a@xxxxxx> wrote:
On Monday 08 May 2017, Carlos E. R. wrote:
On 2017-05-08 08:17, RĂ¼diger Meier wrote:
On 05/07/2017 11:27 PM, Carlos E. R. wrote:
$ man wipefs

cer@Telcontar:~> man wipefs | grep -i gpt

Maybe just read it ...

What for? If it doesn't mention GPT specifically, it is no good.

Does dd mention gpt specifically?

No, don't tell us to erase the entire disk: that will work but is
terribly slow on an USB stick.

You have still not read the man page ...:

wipefs can erase filesystem, raid or *partition-table signatures*
(magic strings) from the specified device to make the signatures
invisible for libblkid.

wipefs *does not erase* the filesystem itself nor *any other data*
from the device. When used without any options, wipefs lists all
visible filesystems and the offsets of their basic signatures.

We need tools specific to erasing GPT tables.

wipefs can handle gpt and many other partition tables (GPT, MBR, Sun,
SGI and BSD ) and even more. wipefs is exaclty the right tool to be
used here. It's made for nothing else than such use cases like the OP
posted. If it does not work then it would be a bug.

If you know how to do that, tell us instead of telling us to peruse
man pages without knowing what exactly to seek for.

$ wipefs -fa /dev/sdX

Or just test it on a file:

$ truncate -s 100M /tmp/test.img
$ echo -e "w\nY" | gdisk /tmp/test.img
$ gdisk -l /tmp/test.img | grep -A4 "Partition table scan:"
Partition table scan:
MBR: protective
BSD: not present
APM: not present
GPT: present

$ time wipefs -fa /tmp/test.img
/tmp/test.img: 8 bytes were erased at offset 0x00000200 (gpt): 45 46 49.
/tmp/test.img: 8 bytes were erased at offset 0x063ffe00 (gpt): 45 46 49.
/tmp/test.img: 2 bytes were erased at offset 0x000001fe (PMBR): 55 aa ..

real 0m0.021s
user 0m0.000s
sys 0m0.002s

$ gdisk -l /tmp/test.img | grep -A4 "Partition table scan:"
Partition table scan:
MBR: not present
BSD: not present
APM: not present
GPT: not present

As you see in wipefs output (offsets), it invalidates the GPT table, the
backup GPT table and the (protective) MBR by writing 20 NULL bytes to
the disk.

Seeing that result, it is clear wipefs does the job.

Reading the man page, I had no certainty at all. It doesn't mention
partition tables of any kind.

I did peruse the man page, but I didn't notice these things. Saving this
email for future reference, thanks :-)

Cheers / Saludos,

Carlos E. R.

(from 42.2 x86_64 "Malachite" (Minas Tirith))

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