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Subject: Re: Destroy GPT partition scheme absolutely, how?
To: "Hartmann, O." <ohartman@mail.zedat.fu-berlin.de>,
 FreeBSD CURRENT <freebsd-current@freebsd.org>
References: <20160926150109.0d0d793e@hermann>
From: Miroslav Lachman <000.fbsd@quip.cz>
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Date: Mon, 26 Sep 2016 15:39:19 +0200
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Hartmann, O. wrote on 09/26/2016 15:01:

[...]

> Using a fresh/new SD or USB resolves the problem. But the question
> remains: how can I destroy any relevant GPT information on a Flash
> drive (or even harddisk) to avoid unwanted remains of an foul image
> installation?
>
> First guess was to write the last couple of bytes on such a flash drive
> by letting dd(1) counting backwards, but I couldn't figure out how to
> let dd(1) do such a procedure. The nightmare didn't end, while trying,
> the SD flash card died :-(

I use dd if=/dev/zero almost everytime when I need to install system on 
used HDD.

I rewrite about 10MB on its start and then about 10MB on the end.
I have some script to do this - simply takes media size from diskinfo 
command, substract 10MB and then dd with seek

Hope that it will help you

Miroslav Lachman