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

[Chris Rees]

On 16 September 2012 10:23, Julian H. Stacey <jhs at berklix.com> wrote:
> This is a resend as Benjamin Kaduk <kaduk at mit.edu>
> dropped the
>         Yuri <yuri at rawbw.com>
> from CC line, & Yuri was the original first poster in thread who
> my patch would presumably have helped.
>
> Reference:
>> From:         Benjamin Kaduk <kaduk at mit.edu>
>> Date:         Sat, 15 Sep 2012 14:49:41 -0400 (EDT)
>> Message-id:   <alpine.GSO.1.10.1209151448200.861 at multics.mit.edu>
>
> Benjamin Kaduk wrote:
>> On Sat, 15 Sep 2012, Julian H. Stacey wrote:
>>
>> > I have been applying this diff to my man fdisk:
>> >
>> > http://berklix.com/~jhs/src/bsd/fixes/FreeBSD/src/gen/sbin/fdisk/
>> >
>> > *** 8.0-RELEASE/src/sbin/fdisk/fdisk.8      Sat Mar 14 22:32:16 2009
>> > --- new-generic/src/sbin/fdisk/fdisk.8      Sat Mar 14 22:35:10 2009
>> > ***************
>> > *** 462,464 ****
>> > --- 462,468 ----
>> >  The
>> >  .Xr bsdlabel 8
>> >  command must be used for this.
>> > + .Pp
>> > + When running multi user, you cannot write unless you first run this:
>> > + .br
>> > + sysctl kern.geom.debugflags=16
>> >
>> > I never submitted it as a send-pr,
>> > anyone think I should submit it to help save people ?
>>
>> We have had a long discussion about kern.geom.debugflags starting here:
>> http://lists.freebsd.org/pipermail/freebsd-current/2011-October/028090.html
>> My understanding from that discussion is that your patch should not be
>> accepted.
>
> Got to travel now, will read that thread later,
>
> A shame if we would leave fdisk crippled undocumented, when so easy
> to doc. the solution. Fdisk is known across many OSs Unix & beyond,
> our BSD tools may be better nicer, but fdisk it what many will first
> reach for,
>  a shame not to help newer people & visitors used to fdisk.
> We inside FreeBSD crippled fdisk by adding these flags. Outsiders
> wont expect the weirdness & get impression FreeBSD has a bug.

I think you have a point, but at the moment fdisk really doesn't work
properly at all; I find so many people complaining on IRC about "Why
doesn't fdisk work?"

To be honest, I'd be happy with replacing fdisk with a huge warning
"USE GPART!!"; fdisk isn't really standard anyway.

The alternative of course is to fix fdisk...  *properly*.

Chris