grub: how to boot into ISO partition

See my answer on your boot-from-ISO-files question. Using that as a starting point, I ran some tests with an old hard-drive. I've previously configured Grub2 to boot a multi-ISO flash drive, so what I did was:

1. Create a couple of partitions on an old hard drive. This was done using a USB-to-IDE adapter, so the drive appears as /dev/sdb.

   • Partition 1: FAT32, ~2GB in size
   • Partition 2: unformatted

   
   

2. Mounted the first partition to /mnt and installed a copy of Grub from my system onto the drive:

   sudo grub-install --no-floppy --root-directory=/mnt /dev/sdb
   

   
   

3. "Burned" an ISO to the second partition:

   sudo dd if=avg.iso /dev/sdb2
   

   
   

4. This is an AVG virus-scanner ISO; on my multi-ISO flash drive, I use this to boot the ISO directly:

   menuentry "AVG Rescue CD" {
      loopback loop /iso/avg.iso
      linux (loop)/isolinux/vmlinuz max_loop=255 vga=791 init=linuxrc iso-scan/filename=/iso/avg.iso
      initrd (loop)/isolinux/initrd.lzm
   }
   

   In order to make this work from a hard drive partition, we need to nix the loopback command and set the root device and such. My attempts to have Grub2 discover the root device automagically all failed, so I pointed it at the partition directly. This works, but watch out for Grub's device enumeration; the drive you're trying to boot from may not be (hd0). Here's a working entry for the ISO partition:

   menuentry "AVG Rescue CD" {
      linux (hd0,2)/isolinux/vmlinuz max_loop=255 vga=791 init=linuxrc
      initrd (hd0,2)/isolinux/initrd.lzm
   }
   

   This results in a bootable ISO-on-partition.
   

This works because Grub2 can read ISO9660 filesystems, because this particular ISO is loading an OS that can cope with an ISO on a partition, and because practically everything the kernel loads is in the initrd.

---

If you're using Grub4DOS or Grub 1, you may be able to pull a similar trick with the chainloader. Presuming that this works to boot the Win7 ISO directly (source):

title Windows 7
  map (hd0,0)/win7.iso (hd32)
  map --hook
  chainloader (hd32)

You may have luck with this modification (assuming you "burned" the ISO to the second primary partition, (hd0,1); otherwise substitute the proper partition):

title Windows 7
  map (hd0,1) (hd32)
  map --hook
  chainloader (hd32)

You may also get away with this:

title Windows 7
  chainloader (hd0,1)

However, the ISO isn't really configured to boot from a drive, so you may run into other problems.