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Date: Fri, 14 Sep 2012 17:29:22 -0700
Message-ID: <CAGH67wS0-kFoP=Ae_2-HGNKV2HsdabCo1w9T-VWQ5fQipj1T9w@mail.gmail.com>
From: Garrett Cooper <yanegomi@gmail.com>
To: Yuri <yuri@rawbw.com>
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Cc: freebsd-hackers@freebsd.org
Subject: Re: Why fdisk can't open root disk with MBR for writing?
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On Fri, Sep 14, 2012 at 5:19 PM, Yuri <yuri@rawbw.com> wrote:
> I am trying to change the active partition in MBR.
> This should be a matter of changing only two bits (clearing one in one byte
> and setting another one in another byte).
>
> However, fdisk complains:
> fdisk: Failed to write MBR. Try to use gpart(8).
>
> truss reveals that fdisk failed to open the root disk for writing:
> open("/dev/ad4",O_RDWR,00)                       ERR#1 'Operation not
> permitted'
> open("/dev/ad4",O_RDONLY,00)                     = 3 (0x3)
> ...
> ...
> pwrite(0x3,0x34048200,0x200,0x0,0x0,0x0)         ERR#9 'Bad file descriptor'
> Failed to write MBR. Try to use gpart(8)
>
> The question is: why the disk can't be open RW under root?
> The secondary issue is the bug in fdisk: once -a option is supplied and it
> can't open it RW it should just say so, and not suggest using gpart because
> gpart will probably have the same issue.

1. What version of FreeBSD?
2. What do you have set for kern.geom.debug_flags?
3. Is /dev/ad4 (or any partitions / slices under it) currently in use?

Thanks!
-Garrett