Set Kernel Root to Same Partition as Boot

Question

Running GRUB, I want to set the kernel root parameter to the same partition (or more generically, to a partition on the same device) as the disk with the bootloader.

Initially, the install set the GRUB menu item to pass /dev/XX as the root parameter:

title XXXXX
    root (hd#,#)
    kernel /boot/vmlinuz-XXXX root=/dev/XX1 resume=/dev/XX2 splash=silent quiet showopts vga=0x###
    initrd /boot/initrd-XXXX

I can change the kernel line to reference my disk's label, increasing its tolerance for appearing in various orders:

    kernel /boot/vmlinuz-XXXX root=LABEL=??? resume=LABEL=swap? splash=silent quiet showopts vga=0x###

I would like to change that line so that I can reference the boot partition, whether it's /dev/sda2 or /dev/hdb6, or even better to reference only a partition number, which the kernel will interpret relative to the boot partition (root (hd#,#) in GRUB).

Answer 1

For a proper installation of grub, this information is irrelevant. You do not need to specify which partition is your /boot as long as it is mounted when you're installing grub. Grub saves in MBR the device (disk) and location of vmlinuz and/ initrd during the installation and a further reference in the grub config is not needed there after.

EDIT

After clarifying that you want "to reference your root partition in relation to your boot partition". There is no option that I know ready for this functionality, but you can add it yourself (so scratch my last comment here). This will involve modifying the init script from your initrd image. E.g. you can add a parameter like bootrel=+1 in your kernel line and add some code to initrd image to find out where is the boot partition and then check the bootrel parameter to find the root partition and set the root parameter accordingly.

This is of-course an overcomplicated and hackish way. Perhaps you're approaching your problem wrong. If you describe more generally what you need to achieve, then maybe someone will offer a more option.