Loader, MBR and the boot process

Matthew Seaman m.seaman at infracaninophile.co.uk
Mon Jan 25 09:45:42 UTC 2010

Andriy Gapon wrote:
> on 25/01/2010 04:41 Robert Noland said the following:
>> On Mon, 2010-01-25 at 07:57 +1100, Mark Andrews wrote:
>>>      offset  The offset of the start of the partition from the beginning of
>>>              the drive in sectors, or * to have bsdlabel calculate the correct
>>>              offset to use (the end of the previous partition plus one, ignor-
>>>              ing partition `c'.  For partition `c', * will be interpreted as
>>>              an offset of 0.  The first partition should start at offset 16,
>>>              because the first 16 sectors are reserved for metadata.
>> Ok, now this has my attention... My gut feeling right now is that this
>> is a bug in geom_part_bsd.  I don't understand why the label isn't
>> protected.  (Adding -b 16 when adding the swap partition fixes this)
>> Another project to goes on my list...
>> If anyone knows why this is done like this... please share.
> I presume that this is for purely historic reasons.

I believe this has been known about since 5.x days:


As far as I recall, sometime around 6.1-RELEASE this should have been
fixed.  It certainly seems to be the case that it is harmless to have 
a plain swap partition start at offset 0, but anything else, like encrypted
swap or putting a filesystem there needs the 16 sector offset.



Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP: http://www.infracaninophile.co.uk/pgpkey     Ramsgate
                                                  Kent, CT11 9PW

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