I do not believe that SD cards respond to pure raw block writes from dd. Not unless the stream looks like files.
I run into the same discovery some time ago. If I remember correctly, dd didn't overwrite the content even with random data. It could behave different for different firmware, but I tried a few with the same result. Tomas On Mar 7, 2018 9:13 AM, "wes" <p...@the-wes.com> wrote: that's only if you want to generate a certain size. otherwise it just keeps going until it runs out of blocks to fill. -wes On Tue, Mar 6, 2018 at 5:08 PM, Tim Garton <garton....@gmail.com> wrote: > Don't you need a "count=#" option to dd as well? Not at a computer right > now otherwise I'd be able to check if that's the case... > > On Mar 6, 2018 5:02 PM, "Richard England" <rlengl...@frontier.com> wrote: > > > On 03/06/2018 04:20 PM, Tomas Kuchta wrote: > > > >> Try to delete the original files first. Then create empty file using > >> /dev/zero and copy it to the card. I bet that it will be there on the > card > >> and some of your original data will disappear as result. > >> > >> My guess is that the card controller is deduplicating your /dev/zero > >> blocks > >> trying to protect the card from writes. > >> > >> Tomas > >> > >> On Mar 6, 2018 7:09 PM, "Russell Senior" <russ...@personaltelco.net> > >> wrote: > >> > >> On Tue, Mar 6, 2018 at 3:04 AM, Russell Senior > >>> <russ...@personaltelco.net> wrote: > >>> > >>>> On Tue, Mar 6, 2018 at 3:01 AM, Jim Karlock <jjkarl...@gmail.com> > >>>> wrote: > >>>> > >>>>> My initial attempt to google this was unsuccessful (most people point > >>>>>> out the write protect tab, not my problem). > >>>>>> > >>>>> > >>>>> Bad switch on the write protect tab? (The tab operates a tiny > switch.) > >>>>> > >>>> Nope. > >>>> > >>>> I can turn the switch to lock and it mounts the device read only very > >>>> clearly. The behavior I observe is that it happily writes /dev/zero > >>>> over the block device, but then when I read again, the old data is > >>>> still present. > >>>> > >>> For example, if I flip the tab to write protect tab to "Lock", I get > >>> this: > >>> > >>> # dd if=/dev/zero of=/dev/sdc status=progress bs=1M > >>> dd: failed to open '/dev/sdc': Read-only file system > >>> _______________________________________________ > >>> PLUG mailing list > >>> PLUG@pdxlinux.org > >>> http://lists.pdxlinux.org/mailman/listinfo/plug > >>> > >>> _______________________________________________ > >> PLUG mailing list > >> PLUG@pdxlinux.org > >> http://lists.pdxlinux.org/mailman/listinfo/plug > >> > > > > |Perhaps using dd if=/dev/urandom |of=/dev/sdc status=progress bs=1M > > ...just a thought. > > > > _______________________________________________ > > PLUG mailing list > > PLUG@pdxlinux.org > > http://lists.pdxlinux.org/mailman/listinfo/plug > > > _______________________________________________ > PLUG mailing list > PLUG@pdxlinux.org > http://lists.pdxlinux.org/mailman/listinfo/plug > _______________________________________________ PLUG mailing list PLUG@pdxlinux.org http://lists.pdxlinux.org/mailman/listinfo/plug _______________________________________________ PLUG mailing list PLUG@pdxlinux.org http://lists.pdxlinux.org/mailman/listinfo/plug