Why fdisk can't open root disk with MBR for writing?

[Warren Block]

On Fri, 14 Sep 2012, Yuri wrote:

> On 09/14/2012 19:23, Warren Block wrote:
>> Did you actually try gpart?  GEOM prevents writes to providers that are in 
>> use, but gpart should handle it correctly if the problem is just that fdisk 
>> doesn't understand GEOM.
>> 
>> # gpart set -a active -i 1 ada0
>> 
>> If that fails, the provider is in use, usually mounted.  The safety can be 
>> disabled, but it's better to figure out what has it in use. 
>
> Yes it is the hard drive with mounted /. But changing the active slice should 
> be safe in any case.
> gpart worked.
> This safety feature is protecting people from themselves. Sounds very 
> familiar.

gpart allowed it, so it's not the safety feature but merely that fdisk 
is aging and can't deal well with GEOM.