linux/doc/Hybrid-Boot

3-in-1 Hybrid Boot Disk (BIOS/UEFI)

This guide shows how to prepare a disk on Ubuntu to be bootable from BIOS, 32-bit and 64-bit UEFI with Secure Boot enabled. The intention is to create a bootable USB stick that can be used to boot a rescue system.

All commands should be executed as root.

For more technical information, see the notes section at the end.

Grub will be used as the bootloader. Install the following packages:

apt install grub-efi-amd64-bin grub-efi-ia32-bin grub-pc-bin
apt install grub-efi-amd64-signed # grub-efi-ia32-signed not available on Ubuntu

Partitioning

• The GUIDs are fixed for easier setup with Windows
• The last partition is optional: it can be used to make changes of Ubuntu persistent
• Set the dev variable accordingly

dev=/path/to/dev

sgdisk --disk-guid=4b534944-4949-4949-b741-44495858580a $dev

sgdisk --new=1:1M:+1M      --typecode=1:ef02 --partition-guid=1:42555247-4949-4949-b741-44495858580a $dev
sgdisk --new=2:2M:+14M     --typecode=2:ef00 --partition-guid=2:49494645-4949-4949-b741-44495858580a $dev
sgdisk --new=3:16M:+496M   --typecode=3:2700 --partition-guid=3:524e4957-4945-4949-b741-44495858580a $dev
sgdisk --new=4:512M:+2048M --typecode=4:8300 --partition-guid=4:4e554255-5554-4949-b741-44495858580a $dev
sgdisk --new=5:2560M:4G    --typecode=5:8300 --partition-guid=5:50534143-5245-4949-b741-44495858580a $dev
sfdisk -A $dev 1

Format

• Run partprobe before working with the disk references below
• The labels are set for easier configuration of GRUB
• The first partition is not formatted as it will be used by GRUB to store its executable code

mkdosfs -F 16 -n hybrid-boot   /dev/disk/by-partuuid/49494645-4949-4949-b741-44495858580a
mkntfs     -Q -L hybrid-winre  /dev/disk/by-partuuid/524e4957-4945-4949-b741-44495858580a
mkfs.ext4     -L hybrid-ubuntu /dev/disk/by-partuuid/4e554255-5554-4949-b741-44495858580a
mkfs.ext4     -L casper-rw     /dev/disk/by-partuuid/50534143-5245-4949-b741-44495858580a

Install GRUB

• Set the mnt variable accordingly

mnt=/path/to/mount

mount /dev/disk/by-partuuid/4e554255-5554-4949-b741-44495858580a $mnt
mkdir -p $mnt/boot/efi
mount /dev/disk/by-partuuid/49494645-4949-4949-b741-44495858580a $mnt/boot/efi

grub-install --root=$mnt --removable --no-nvram --uefi-secure-boot --target=x86_64-efi $dev
grub-install --root=$mnt --removable --no-nvram --uefi-secure-boot --target=i386-efi   $dev
grub-install --root=$mnt --modules='ext2 part_gpt'                 --target=i386-pc    $dev

Place the following configuration snippets in $mnt/boot/grub/grub.cfg.

Ubuntu

menuentry 'Ubuntu' {
	search --set --label hybrid-ubuntu
	linux /casper/vmlinuz boot=casper ignore_uuid persistent
	initrd /casper/initrd
}

The persistent parameter is only useful, if the persistence partition was created.

Windows

menuentry 'Windows (UEFI)' {
	search --set --label hybrid-boot
	chainloader /EFI/Microsoft/Boot/bootmgfw.efi
}

menuentry 'Windows (BIOS)' {
	search --set --label hybrid-winre
	ntldr /Boot/bootmgr
}

Copy OS Files

Ubuntu

• Set the cdrom variable accordingly

cdrom=/path/to/ubuntu-iso

cp -r $cdrom/casper $cdrom/preseed $mnt

Windows

• Set the cdrom and winre variables accordingly

cdrom=/path/to/windows-iso
winre=/path/to/winre-mnt

mount /dev/disk/by-partuuid/524e4957-4945-4949-b741-44495858580a $winre

wim=$cdrom/sources/install.wim

dir=$winre/Recovery
mkdir $dir
7z e -o$dir $wim 1/Windows/System32/Recovery/Winre.wim
7z e -o$dir $wim 1/Windows/System32/boot.sdi

dir=$winre/Boot
mkdir $dir
7z e -o$dir $wim 1/Windows/Boot/PCAT/bootmgr

dir=$mnt/boot/efi/EFI/Microsoft/Boot
mkdir -p $dir
7z e -o$dir $wim 1/Windows/Boot/EFI/bootmgfw.efi

BCD

Copy winre-uefi.bcd and winre-bios.bcd:

cp winre-uefi.bcd $mnt/boot/efi/EFI/Microsoft/Boot/BCD
cp winre-bios.bcd $winre/Boot/BCD

Windows Hybrid Boot

Windows can not be booted from BIOS and UEFI with the same configuration.

The above procedure enables Windows to boot using UEFI.

Do not use sgdisk for MBR modifications, because it wipes the MBR boot code of GRUB.

Boot from BIOS

Windows needs an MBR to boot from BIOS:

printf 'label-id:0x4b534944\n1,0x7fff,ee,*\n0x8000,0xf8000,27' | sfdisk -Y dos $dev

If you try to boot without the above configuration, the following message appears in the blink of an eye:

ata1 master: Unknown device

Boot from UEFI

Remove the hybrid MBR:

printf 'label-id:0x00000000\n1,,ee,*' | sfdisk -Y dos $dev

If you try to boot without the above configuration, the following message appears:

BlInitializeLibrary failed 0xc00000bb

Notes

BIOS Boot

GRUB does not need the active/bootable flag, but some BIOS firmwares check for it and refuse to boot, if it is not present. The following message may appear:

Non-System disk or disk error
replace and strike any key when ready

To improve hybrid booting capability, the flag is always set on the first partition.

Windows Bootloaders

The Windows bootloader is configured using a file called BCD (Boot Configuration Data). The file is a binary Windows Registry file and references IDs from the partition table. This can make Windows boot problems cumbersome to fix.

The above BCD files are usable if the disks were created using the described IDs. They were created in a VM using BCDEdit: create-winre-uefi.bat and create-winre-bios.bat.

The UEFI bootloader bootmgfw.efi uses the disk and partition GUIDs from the GPT. The BIOS bootloader bootmgr uses the disk signature and partition start offsets in the MBR.

To change GUIDs in a BCD, partitions with the same GUIDs can be recreated in a VM and BCDEdit can be used to recreate a BCD: create-minimal.bat.

Alternatively hivexsh can be used to change the GUIDs in an existing BCD.

Casper Persistence

The casper manual mentions the use of a file, but this only works on FAT, see find_cow_device in casper-helpers.