fdisk incompatibility between major versions

[Freddie Cash]

On Mon, May 25, 2009 at 10:35 AM, Robert Huff <roberthuff at rcn.com> wrote:
>   Due to a combination of my spectacular stupidity and external events, a
> machine running -Current from late April will no longer boot.  Specifically,
> instead of the loader menu screen I get "Invalid partition".
>   Crud.
>   Broke out the most recent fixit disk, which is from 7.1 (Jan 2009).
>   Boots fine; fdisk finds the correct slice information; bsdlabel finds the
> right partition data; mount / and /usr under LiveFS
>   Whew!!!!
>   So ... I'm guessing the problem in the boot code is corrupted, and if I do
>
>    fdisk -B -b <path to -CURRENT boot blocks> da0
>
>    it should put things back to normal.
>    However: when I do the second commit I get
>
>    fdisk: Geom not found "da0"
>    fdsk: failed to write sector 0

In order to alter a drive with a mounted filesystem (ie an active
drive), you need to first set the drive to writable:

sysctl -w kern.geom.debugflags=16

This has been the case for several years now (since 5.x I believe).

-- 
Freddie Cash
fjwcash at gmail.com