Booting 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.

Writing this image to a USB stick will permanently erase all existing data on the device. Additionally, the stick will no longer be usable for general data storage. Most USB sticks are pre-formatted with a FAT32 or exFAT Windows filesystem, and to keep the existing data 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 that allows you 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. FAT32 is widely supported on USB sticks. For hard drives, any filesystem supported by grub is also appropriate.

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

The following procedure expects an existing Grub2 installation on your hard drive or USB stick.

Copy the ISO image to a folder of your choice on your hard drive. For example, create a folder called “iso” in the root of your hard drive and copy the ISO image there:
```
sudo mkdir /iso
sudo cp some-kiwi-live.iso /iso/
```
Look up the root filesystem UUID of your current operating system. Get this information by running the command:
```
findmnt -n -o UUID /
```

Add the following submenu setup to the grub.cfg file:

Note

Verify that the path to the ISO image is correct. Set your own menu name. The drive identification for Grub2 can be checked at boot time by pressing the ‘c’ key and typing ‘ls’. The following example assumes a live ISO image for the x86_64 architecture. Adjust the paths to kernel and initrd if you have a different architecture.

menuentry "Boot from Live ISO" {
    load_video
    set gfxpayload=keep
    insmod gzio
    insmod part_gpt
    insmod iso9660
    insmod btrfs
    insmod ext2
    insmod xfs
    insmod lvm
    insmod loopback
    search --no-floppy --fs-uuid --set=root UUID_FROM_STEP_2
    set isofile="/iso/some-kiwi-live.iso"
    set kernel="(loop)/boot/x86_64/loader/linux"
    set initrd="(loop)/boot/x86_64/loader/initrd"
    set options="rd.live.image root=live:CDLABEL=CDROM"
    loopback loop $isofile
    linux $kernel iso-scan/filename=$isofile $options
    initrd $initrd
}

Restart your computer and select the added menu entry.

Note

For USB sticks, the procedure is identical. You would install Grub2 on the USB drive and follow the steps above. However, it is uncommon to have Grub2 already installed on a USB stick. To simplify the setup, there are good helper tools such as MultiOS-USB.

Booting Install ISO Images from Grub2

The install ISO image created for an OEM disk image via the installiso="true" attribute supports the “iso-scan/filename” feature as well. The procedure is the same as for live ISO images, only the boot options differ. The following example assumes the default install ISO volume ID INSTALL:

menuentry "Install from ISO" {
    load_video
    set gfxpayload=keep
    insmod gzio
    insmod part_gpt
    insmod iso9660
    insmod btrfs
    insmod ext2
    insmod xfs
    insmod lvm
    insmod loopback
    search --no-floppy --fs-uuid --set=root UUID_FROM_STEP_2
    set isofile="/iso/some-kiwi.install.iso"
    set kernel="(loop)/boot/x86_64/loader/linux"
    set initrd="(loop)/boot/x86_64/loader/initrd"
    set options="cdinst=1 root=install:CDLABEL=INSTALL"
    loopback loop $isofile
    linux $kernel iso-scan/filename=$isofile $options
    initrd $initrd
}

Alternatively, the grub configuration of the ISO image itself can be used through the loopback.cfg file provided on all KIWI NG ISO images. The ISO path must be passed via the iso_path variable. Depending on the distribution, the grub directory on the ISO image is named grub2 or grub:

menuentry "Install from ISO" {
    insmod loopback
    search --no-floppy --fs-uuid --set=root UUID_FROM_STEP_2
    set iso_path="/iso/some-kiwi.install.iso"
    export iso_path
    loopback loop $iso_path
    configfile (loop)/boot/grub2/loopback.cfg
}

Note

ISO File on the Install Target Disk

If the disk selected as installation target holds the ISO file, the installation would overwrite the ISO file while reading from it. In this case KIWI NG copies the ISO file into main memory and releases the disk before the image is dumped. Make sure the system has enough main memory to store the ISO file plus an additional 512 MB. If there is not enough memory available, the installation stops before the target disk is modified.