How to restore a USB drive converted to bootable

[Warren Block]

On Sat, 2 May 2015, Polytropon wrote:

> On Sat, 02 May 2015 09:20:09 -0453, William A. Mahaffey III wrote:
>> On 05/02/15 09:06, Lowell Gilbert wrote:
>>> "William A. Mahaffey III" <wam at hiwaay.net> writes:
>>>
>>>> I am about to do some OS installs (NetBSD & OpenBSD, as it happens) on
>>>> boxen under construction. I would also like to use UBCD on a flash
>>>> drive to memcheck those boxen prior to installation. If I prep a USB
>>>> thumb drive as either a bootable UBCD drive or an over-the-WWW
>>>> installer, I wipe out the drive for its original use. Is there a way
>>>> to restore the drive back to its original functionality if I wanted to
>>> Is "wipe the drive and reformat" what you need to hear, or do you have
>>> more requirements that you haven't made clear?
>>>
>>
>>
>> Wipe & reformat, preferably from CLI under FBSD 9.3R-p13 for
>> convenience, is what I'm after. Clearly creating a bootable UBCD or
>> installer will wipe out whatever was
>> there before, so I just want to get back to 'virgin' USB drive.
>
> In that case, the command
>
> 	# dd if=/dev/zero of=/dev/da0 bs=1m count=1
>
> should be fine. If there is any offending GPT metadata located
> at the end of the USB drive, estimate the size and also erase
> the last few MBs (use skip= to do so). There is no need to
> actually zero out the _whole_ drive.

It is easier to use gpart, and it will correctly remove whichever 
partitioning metadata is present:

gpart destroy -F <device>