Date: Sun, 1 Dec 2019 11:28:03 +0100 From: Gary Jennejohn <gljennjohn@gmail.com> To: freebsd-usb@freebsd.org Subject: Re: pendrive clone impossible ? Message-ID: <20191201112803.7c7677d4@ernst.home> In-Reply-To: <20191201131416.3a1554ec@asd2> References: <CAFYkXjkHobPfNwCL3ssL98TgUjE=jvojXACH%2BiR0EV-tzK-pxA@mail.gmail.com> <20191130223322.1028feab.freebsd@edvax.de> <CAFYkXjk3HOmfXkd=L2CYpbV9=YmzP_dP1RxS37D817iW_Bqftg@mail.gmail.com> <20191130234900.81464b43.freebsd@edvax.de> <CAFYkXj=8md=Lv-N9CLLZ=kU%2BaEE8VZGVu=3kQTWnvqbGi6tmQA@mail.gmail.com> <20191201050341.4a02879a@asd2> <CAFYkXj=OdpDf7hzCrYzmFMqRObdzqj=KkY863UG3nhWbnnRtKA@mail.gmail.com> <20191201082801.6a8c7639@ernst.home> <20191201131416.3a1554ec@asd2>
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On Sun, 1 Dec 2019 13:14:16 +0300 Anatoly <anatoly@kazanfieldhockey.ru> wrote: > On Sun, 1 Dec 2019 08:28:01 +0100 > Gary Jennejohn <gljennjohn@gmail.com> wrote: > > > The geom code protects certain parts of the data area on the > > drive, in particular GPT/MBR areas, unless ``sysctl > > kern.geom.debugflags=16'' is run beforehand. One can see this in > > many places in the geom code. > > > > I always set this sysctl when I know I'm going to overwrite the > > first sectors of a drive. > > > Interesting, but I've succefully overwrited MBR many times > on FreeBSD 5.x-11.x without setting this sysctl. > I've learned about this sysctl when I first time failed to overwrite bsd > label inside MBR slice under FreeBSD 7.1 with dd (but not MBR). There > was explicit write error, not just silent succeful write to nowhere. I > may be wrong, but as I remember, I newer got this trouble again > starting from 10.x. > Is there something new on 12.x? > This sysctl has been around for quite some time. I added a shellscript to my ~/bin to set it in 2015. IIRC Julian Elischer requested it because he had problems initializing disks. I just use it by default when I write to the first sectors on a disk. There is geom code which explicitly checks whether debugflags is set to 16. I have not looked at the code to see what happens when that is the case. -- Gary Jennejohn
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