Re: EasyBCD and GRUB2

[S O]

Thanks for advise. I countered this issue by issuing all relevant insmod's in master grub.cfg file before the menu, but chainloading is a better solution indeed.

However, right now the whole scheme stopped working altogether after adding one more Linux instance partition.

Now GRUB comes up with initial value of prefix not for the master partition, but for new added partition.

I use /dev/sda2 for master grub partition, and that is where GRUB used to come from while I had two Linux instances, but adding third Linix instance to /dev/sda8 caused master grub to come up with Linux3's grub.cfg. I thought may be Linux3 install somehow may have screwed up /dev/sda2 (even though grub.cfg there is intact), so I rebuilt /dev/sda2 and re-created EasyBCD entry just in case, but it did not help.

To verify that grub-install invokes grub-mkimage with correct --prefix value I embedded printout statement into grub-install before all invocations of grub-mkimage. Printout displays correct expected value for prefix "(,msdos2)/boot/grub" passed to grub-mkimage --prefix.  

Yet when I run "strings" or "grep" on produced core.img I do not see this prefix string or any parts of it (such as "msdos", "boot" or "grep") inside produced core.img.

Is core.img compressed or is prefix string otherwise somehow scrambled inside core.img -- or does its absence in plain text in core.img means the failure of grub-mkimage to embed the prefix string?

At a glance, I do not see any compression option in grub-install, so I assume core.img is likely to be uncompressed and requested prefix string then indeed may be missing in core.img?

---

From: Andrey Borzenkov <address@hidden>
To: S O <address@hidden>
Cc: "address@hidden" <address@hidden>
Sent: Tuesday, December 25, 2012 10:58 PM
Subject: Re: EasyBCD and GRUB2

On Wed, Dec 26, 2012 at 8:55 AM, S O <address@hidden> wrote:
> menuentry "MyLinux2" {
>    search --no-floppy --set root --label MYLINUX2
>    set prefix=($root)/boot/grub
>    configfile $prefix/grub.cfg
> }
>
> and so on.
>
> Thus GRUB is actually loaded only from master partition (which should reduce
> the risks of "blocklist" issues in case of backups etc.), but then menu
> directs it to instance-specific partition and grub.cfg in that partition.

Word of caution. ${prefix} also defines location of grub2 modules. So
you have to absolutely ensure that grub2 build in every OS is the same
as master. Otherwise you are risking running binaries from different
builds with undefined results.

I would rather use chain loading; you can directly load core.img using

chainload $prefix/i386-pc/core.img

(or x84_64-efi or rather exotic i386-efi)

which ensures your core.img and modules are consistent. There is no
blocklists involved, grub2 will read files so you are free to move
them around as you like.