Re: Dual Boot

[Jan Bakuwel <jan.bakuwel@gmail.com>]

Hi Pascal,

Thanks for responding.

On 26/11/16 11:01, Pascal Hambourg wrote:
> Le 25/11/2016 à 19:31, Jan Bakuwel a écrit :
>>
>> For reasons beyond my understanding grub complains about being
>> installed in a partition instead of the MBR ("embedding is not
>> supported and a BAD idea", yet it works fine).
>
> The GRUB BIOS boot loader is split off in three main parts :
> - the boot image stored in the MBR or in a partition boot sector (PBR)
> - the core image stored in a special area outside a filesystem (called
> "embedding") or as a regular file in a filesystem
> - modules, config files and so on stored in /boot/grub/
>
> The only purpose of the boot image is to load the core image. The boot
> image is a very small program which must fit into a single sector, so
> it does not understand any partition table or filesystem format. It
> reads a hardcoded list of physical sectors ranges ("blocklists") which
> contain the core image.
>
> Embedding of the core image is only (but not always) possible when the
> boot image is in the MBR and there is a big enough "embedded area"
> between the MBR and the first partition on a DOS/MBR partition table
> or a "BIOS boot" partition on a GPT partition table, or when the boot
> image is in a partition boot sector and the partition format contains
> a suitable area for embedding.
>
> I have yet to find such a partition format, so when installing the
> boot image in the PBR of a partition with any usual contents type
> (ext4, LVM physical volume, RAID member...), embedding is not possible.
>
> When embedding is not possible, the core image is stored as a regular
> file in /boot/grub. Then /boot/grub must be on the same drive as the
> boot image. However blocklists are not reliable with files, because
> the filesystem may move blocks containing a file around.

I find it extremely useful (to the point where it once literally saved
me from disaster which is a story beyond the context of this thread) to
have multiple OS-es installed on any machine. I've been doing that for
years and even with grub it has - so far - always worked fine. But I
hear you that that's not a guarantee, and thus I started using extlinux.

Which brings me to the following question: what is the recommended way
to boot multiple OSes with grub, for example with a partition layout as
below. Or is there simply no sane way to do this with grub?

/dev/sda1: boot/rescue system

/dev/sda2: Windows 7
/dev/sda3: Windows 10

/dev/sda5: /boot - Linux system 1
/dev/sda6: / - Linux system 1
/dev/sda7: /var - Linux system 1
/dev/sda8: /var/log - Linux system 1

/dev/sda9: /boot - Linux system 2
/dev/sda10: / - Linux system 2
/dev/sda11: /var - Linux system 2
/dev/sda12: /var/log - Linux system 2

/dev/sda13: swap
/dev/sda14: LVM

best regards,
Jan