Bootcamp, GRUB/LILO and MBR

[Jakob Praher]

hi,

 

first of all: Debian Testing CD has suitable SATA drives for installing Linux. 2.6.14 or later kernels are required. One problem is the network driver, which is not correctly supported by the CD. A driver has to be installed afterwards.

 

I have partitions like this

/dev/sda1 - Small EFI FAT partition

/dev/sda2 - HFS+ partition

/dev/sda3 - ext3 Linux partition

 

I have installed linux as / in ext3. Now after that I was asked to install the boot loader.

Hum. I don't want to render my Macbook unusable. So I chose the following:

 

btw:

cat /boot/device.map

lists /dev/sda as (hd0)

 

But doing the following does not work:

root (hd0,2) # this is sda3

setup (hd0,2)

 

But this does not work.

Since I think that OSX is booting using the efi partition information (which ignores the MBR) it would be ok to simply overwrite the MBR. Has anybody tried this?

 

Thanks in advance

What do you think, why writing GRUB into (hd0,2) is not working?

 

-- Jakob

[Christoph Pfisterer]

But this does not work.

Could you be a bit more specific? Does the installation of grub work? Does it show up in the built-in boot volume chooser (when you press Option on boot)? If yes, how far does the boot process get?

 

Since I think that OSX is booting using the efi partition information (which ignores the MBR) it would be ok to simply overwrite the MBR. Has anybody tried this?

Well, it's a bit more complicated than that. From what I've learned about the EFI aspects of Boot Camp so far, I'd say it works like this:

 

First, detection: The firmware does not check individual partitions for legacy boot code, only the disk as a whole. Probably it simply checks the MBR for valid boot code.

 

Second, actual booting: When you choose to boot from the internal hard disk using Boot Camp, it tries to stay as close to a standard BIOS as possible. That would mean it simply loads the MBR and jumps to it. The rest is up to the boot code stored in the MBR.

 

So, what does that mean? First, you'll need some boot code in the MBR. Installing GRUB on the whole disk will likely destroy the EFI partition table (stored in sectors 1 to 128 or so), so it was the right choice to install GRUB on the Linux partition. The Debian 'mbr' package contains a simple MBR that loads the boot sector of the active partition and starts it.

 

The second problem are the partition tables. Neither GRUB (0.9x) nor the MBR code know about EFI GPT partition tables, they'll just look for the good old MBR partition table. So you'll need to mirror your partitions in the MBR table. Unfortunately, I don't know of a Linux tool that does this. The Boot Camp Assistant does it, maybe diskutil does too, but I haven't tried that. I guess it's time to write such a tool...

[Jakob Praher]

>> But this does not work.

 

>Could you be a bit more specific? Does the installation of grub work? Does it show up in the built-in boot

>volume chooser (when you press Option on boot)? If yes, how far does the boot process get?

 

It simply does not find the partitions (hd0,2) for instance.

So setting root to (hd0,2) takes a long time and fails.

I have not tried setting it to (hd0).

 

Oh and another thing:

After making an image using the apple boot cd, linux does not know the individual partitions anymore. But instead just sees everythign as one big partition. Strangely in MacosX the partition is still there ...

 

-- Jakob

[domino]

I can't confirm this but I can post my experience with Linux installers. If it sees a bootable parition (hda) or bootable partition (hdax) it will prompt you to either install it one of the two. The latest kernela does have support for EFI but I have no experience with that. Maybe install the bootloader on ext3 and enable the efi feature once inside linux.

 

If you still have problems with grub, try lilo instead. The problem with lilo is that it might not detect other boot records but you can at least install it on your ext3 partition. If boot camp can handle triple booting and will recognize a boot record on ext3, then all is good. But if it can't, you'll have to find another alternatives.