Comment 3 for bug 578199

That's just me getting my tracks and cylinders mixed up then. It
should be 'ignore first track'.

The MSDOS convention is to avoid allocating the first 63 sectors (ie
0x10000 lots of 512 bytes about 32K) and that is where grub hides
itself.

Gory details here:
http://people.apache.org/~skitching/MineOfInformation/linux/Booting_Linux_on_x86_with_Grub2.html

For some reason the current parted implementation doesn't follow that
convention with virtual disks - probably because there is no detected
geometry.

Arguably there is a bug in parted as well, although as it is just a
convention not a specification that might not hold.

On 10 December 2010 11:14, Alex Bligh <email address hidden> wrote:
> I may be reading this patch wrong:
>  lp:~brightbox/vmbuilder/exclude-first-cylinder
>
> but that would appear to create the first partition 63 sectors in. If
> so, this is incorrect (note I haven't tried it).
>
> Technically you should get the geometry from the disk, but most disks
> (not all) have 63 sectors per track and 255 heads. 63 sectors is one
> track in, not one cylinder in. Partitions are normally cylinder aligned,
> and you want a full cylinder to allow grub to have room for the MBR.
> Therefore, the first partition should be 63*255 sectors in, i.e. 16065
> sectors, and 16065s is the offset that should be passed to parted, not
> 63s.
>
> --
> You received this bug notification because you are a direct subscriber
> of the bug.
> https://bugs.launchpad.net/bugs/578199
>
> Title:
>  ubuntu-vm-builder builds images with no post-MBR gap
>

--
Neil Wilson