Booting a Live ISO Images from Grub2

In KIWI NG, all generated ISO images are created to be hybrid. This means, the image can be used as a CD/DVD or as a disk. This works because the ISO image also has a partition table embedded. With more and more computers delivered without a CD/DVD drive this becomes important. The deployment of such an image onto a disk like an USB stick normally destroys all existing data on this device. It is also not possible to use USB stick as a data storage device. Most USB sticks are pre-formatted with a FAT32 or exFAT Windows File System and to keep the existing data on the stick untouched a different deployment needs to be used.

Fortunately Grub2 supports booting directly from ISO files. It does not matter whether it is installed on your computer’s hard drive or on a USB stick. The following deployment process copies the ISO image as an additional file to the USB stick or hard drive. The ability to boot from the disk is configured through a Grub2 feature which allows to loopback mount an ISO file and boot the kernel and initrd directly from the ISO file.

The initrd loaded in this process must also be able to loopback mount the ISO file to access the root filesystem and boot the live system. Almost every Linux distribution supports fat32, and more and more of them also support exFAT. For hard drives, Linux filesystems are also supported.

The dracut initrd system used by KIWI NG provides this feature upstream called as “iso-scan/filename”. Therefore all KIWI NG generated live ISO images supports this deployment mode.

The following procedure shows how to setup Grub2 on your hard drive:

  1. Copy the ISO image to a folder of your choice on your hard drive.

  2. Add the following code to the “grub.cfg” file:

    Be sure to set the path to the ISO image, you can set your own menu name. The drive identification for Grub2 can be checked at boot time by pressing the ‘c’ key and typing ‘ls’.

    submenu "Boot from openSUSE ISO" {
     iso_path="(hd0,gpt2)/path/to/openSUSE.iso"
     export iso_path
     loopback loop "$iso_path"
     root=(loop)
     source /boot/grub2/loopback.cfg
     loopback --delete loop
}

  3. Restart your computer and select the added menu.

For USB sticks, the procedure is identical. You would then install Grub2 on the USB drive and follow the steps above. The use of scripts such as “MultiOS-USB” is strongly recommended.