zeroing out part of an SDcard

[Robert P. J. Day]

On Thu, 21 Aug 2014, Robert Moskowitz wrote:

> More on my compressing images from SDcards.
>
> I only need the boot info and 1st partition, so I remove the other partitions,
> but of course there is still 1s out there so it will not compress efficiently.
> I want to zero out the end of the card so first I use fdisk:
>
> # fdisk -l /dev/sdb
>
> Disk /dev/sdb: 7.4 GiB, 7969177600 bytes, 15564800 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: dos
> Disk identifier: 0x0009e2ad
>
> Device Boot Start End Blocks Id System
> /dev/sdb1 8192 1007615 499712 83 Linux
>
> Then dd:
>
> # dd if=/dev/zero of=/dev/sdb bs=1M seek=1007620
> dd: ‘/dev/sdb’: cannot seek: Invalid argument
> 0+0 records in
> 0+0 records out
> 0 bytes (0 B) copied, 0.000652852 s, 0.0 kB/s
>
> ======================
>
> seems you cannot seek on an SDcard. How do I do this? Since the change in
> partition 1 is trivial, if I have to start again from an SDcard with all 3
> paritions, I can do that...

  it seems like you're trying to seek more than a terabyte into that
card.

rday

-- 

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Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

Twitter:                                       http://twitter.com/rpjday
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