On 09/12/2019 21:59, Hendrik Boom wrote:
> On Mon, Dec 09, 2019 at 10:45:46PM +0100, Antony Stone wrote:
>> On Monday 09 December 2019 at 22:38:26, Hendrik Boom wrote:
>>
>>> I have an sd card that used to be in an android phone.
>>> My usual tools tell me very little:
>>>
>>> root@midwinter:~# lsblk --fs /dev/sdb
>>> NAME FSTYPE LABEL UUID MOUNTPOINT
>>> sdb
>>> ├─sdb1
>>> └─sdb2
>>>
>>> root@midwinter:~# fdisk -l /dev/sdb
>>> Disk /dev/sdb: 14.9 GiB, 15931539456 bytes, 31116288 sectors
>>> Units: sectors of 1 * 512 = 512 bytes
>>> Sector size (logical/physical): 512 bytes / 512 bytes
>>> I/O size (minimum/optimal): 512 bytes / 512 bytes
>>> Disklabel type: gpt
>>> Disk identifier: 4F1502F0-81F3-49FA-A294-8B8FB4DB6964
>>
>> I'm really rather surprised that a 16Gbyte SD card is has a GPT partition
>> table.
>
> My guess is that Android put it there and that it's not what was on it
> originally.
>
>>

>>> Device     Start      End  Sectors  Size Type
>>> /dev/sdb1   2048    34815    32768   16M unknown
>>> /dev/sdb2  34816 31116254 31081439 14.8G unknown
>>> root@midwinter:~#

>>>
>>> Is there another way to find out anything?
>>
>> Well, given that it's got a GPT partition table, try sgdisk instead of sfdisk.
>>
>>> Or is this likely to be an Google-encrypted card I can do nothing with
>>> except restore it to an almost virginal state?
>>
>> What do you *want* to do with it?
>>
>> Read it, copy it, reformat it, what?
>
> Read it if I can (and I aready suspect I can't); otherwise reformat
> it to whatever file system it is that most
> consumer devices using microsd cards expect.
> Kind of a factory reset.
>
>>
>>> And what is the proper way to reformat an sdcard to the file
>>> systems just about everything accepts without using
>>> up its remaining lifetime?
>>
>> Hm, dd if=/dev/zero of=/dev/sdb bs=1M count=1
>
> Yes, that will clear it out. But what file system is customarily on a new
> 16G microsd card? And does that fs really need everything cleared out?

No, that will not wipe the GPT or it's backup.
Use something like 'gdisk z /dev/sdb' then dd it after if paranoid.
Confliction between MBR <=> GPT can cause corruption.

>
> -- hendrik
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