Grub and Disk ID

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maltheus · Post by **maltheus** » Tue Mar 31, 2009 5:39 pm

Is there any way to make grub boot off of a disk id (like udevs /dev/disk/by-id) rather than using the hd0 syntax? I want to install Gentoo on a USB drive that can be booted from a boot CD or a vmware image, and run on any computer, so the hard drive number will be different depending on how I run it.

danomac · Post by **danomac** » Tue Mar 31, 2009 5:51 pm

I've seen grub boot by UUID, although I've never actually tried setting it up myself. I do believe ubuntu is one of the distros that boots like that.

Perhaps a quick search of 'grub+uuid' may find better results?

maltheus · Post by **maltheus** » Tue Mar 31, 2009 6:33 pm

Interesting. That gets me half way there. It lets me pass the root drive's uuid to the kernel, but grub still seems to use the BIOS drive number to locate the kernel itself. Anybody have any ideas on specifying the boot partition with a unique id?

DONAHUE · Post by **DONAHUE** » Wed Apr 01, 2009 2:58 pm

Please post your grub.conf and fstab. What are you seeing that makes you say

but grub still seems to use the BIOS drive number to locate the kernel itself

??

maltheus · Post by **maltheus** » Wed Apr 01, 2009 3:07 pm

I haven't put together the system yet, I'm still planning it out. But that was the clear impression I got from googling around. Here's a grub example (and fstab isn't a problem for me):

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title     Ubuntu intrepid (development branch), kernel 2.6.27-7-generic
root      (hd0,0)
kernel    /boot/vmlinuz-2.6.27-7-generic root=UUID=a8aa4adb-b3e6-4e1d-b4ad-e6cd704788b2 ro  
initrd	 /boot/initrd.img-2.6.27-7-generic

You can pass in the root drive UUID to the kernel with the root=UUID= notation, but on the line above it, you still have to specify the hard drive bios number with the (hd0,0) notation (i.e. you can't specify the boot drive UUID). As I understand it, grub itself doesn't really understand UUIDs itself, it can only pass them on.

DONAHUE · Post by **DONAHUE** » Wed Apr 01, 2009 4:57 pm

The (hd0,0) passed by bios to grub is virtually always the drive selected as boot drive by you in your BIOS.
Assuming your motherboard has choices to allow booting a usb drive you can select it in BIOS and use (hd0,0) in the grub root line and root=UUID= in the grub kernel line. This will save trouble with the kernel device naming.

maltheus · Post by **maltheus** » Wed Apr 01, 2009 5:06 pm

DONAHUE wrote:The (hd0,0) passed by bios to grub is virtually always the drive selected as boot drive by you in your BIOS.
Assuming your motherboard has choices to allow booting a usb drive you can select it in BIOS and use (hd0,0) in the grub root line and root=UUID= in the grub kernel line. This will save trouble with the kernel device naming.

Sure, but I want to be able to boot this on any system and I also want to be able to boot this in vmplayer. I'm thinking now, that the way to do this is to put the kernel on the boot CD and everything else on the USB drive. It'll be a pain to have to burn out a new boot CD with every kernel upgrade, but it seems to be the only option here.

Thanks for the tips.

azlan · Post by **azlan** » Thu Apr 02, 2009 4:53 am

you can get the UUID of a device by using this method.

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ls -l /dev/disk/by-uuid

just cut and paste that into a console and you will get all of your disk id's then just try it and see what happens.. (make sure you create a new grub entry so that you can always boot into your old one)

whig · Post by **whig** » Thu Apr 02, 2009 5:02 am

As it stands current kernels don't support root mount by uuid/label. The ubuntu config above did it by using an initrd, which is a small o/s that scans all devices for identifiers. I used the genkernel scripts to build my own initrd for a usb flash only system.