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To: ache@nagual.pp.ru
From: "M. Warner Losh" <imp@bsdimp.com>
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cc: dmp@bitfreak.org
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Subject: Re: Can't change partition table anymore
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In message: <20050404042817.GB49953@nagual.pp.ru>
            Andrey Chernov <ache@nagual.pp.ru> writes:
: On Sun, Apr 03, 2005 at 09:00:12PM -0700, Darren Pilgrim wrote:
: > > I can't write FreeBSD bootloader because reinstalled Windows overwrite it 
: > > with standard MBR and sysinstall don't allow to write bootloader anymore. 
: > > The only thing I not try yet in that situation was 'dd' - I was too lasy 
: > > to find needed byte.
: > 
: > The MBR is the first sector of the disk.  FWIW, if you're coexisting with
: > Windows, it's easier to let Windows have its way with the MBR and use
: > Windows' own boot loader.  The setup is simple, copy a boot sector and edit
: > a text file, and Windows won't mess with it.
: 
: There are a lots of ways. When I don't know kern.geom.debugflags=16 trick 
: yet, I istall 3rd party boot manager under Windows. But all this is not 
: relevant to the discussed subject: why FreeBSD root can't change disk 
: partition without quasi-shamanic dance with unnatural and undocumented 
: sysctls? Why Linux root can do it freely?

As you see in my other mail, this only happens when one partition
overlaps the MBR and that partition has mounted partitions.  Such a
configuration is illegal, but tolerated, in the PC world.

Warner