I am trying to create a universal (BIOS/EFI) bootable USB HDD that can provide me with portable 32-bit & 64-bit ‘Windows To Go’ environments, together with a 64-bit Ubuntu-based distro and 64-bit Debian-based distro of Linux.

Using WinToUSB (which requires MBR tables) I was able to create my 32-bit & 64-bit Windows 10 Pro Windows To Go environments (on separate partitions) which were bootable on both BIOS and EFI systems.

I then installed my 64-bit Ubuntu-based distro in BIOS mode on another partition, after which I could choose to boot into my Windows boot loader from GRUB2.

I became stuck when trying to add EFI-functionality to my Ubuntu-based installation.

To add EFI capability, I tried booting on an EFI-based machine with the Ubuntu-based distro installation media. Then, I attached my USB HDD, mounted the Linux partition and bound the various system directories, then chroot’d to install & update grub which reported successfully finding Linux and adding EFI entries.

However, upon rebooting on the USB HDD, I was only presented with the Windows boot loader for my 32-bit & 64-bit Windows To Go with no sign of GRUB2 in EFI-mode.

A vague post I found suggested I need to run:

grub-install --target x86_64-efi --efi-directory /mnt --boot-directory=/mnt/boot –removable

But there is no mention of what I need to mount to /mnt.

Since my knowledge of Linux is still a work-in-progress and limited, I am hoping you guys could help.

Is it possible to install EFI-based GRUB2 on MBR type USB HDD? If so, how would I get it done without breaking my hybrid dual Windows to Go?

Current MBR Partitions are as follows:

  1. 500MB FAT32 (System Boot)
  2. 80GB NTFS (64-bit Windows 10 Pro Windows To Go)
  3. 80GB NTFS (32-bit Windows 10 Pro Windows To Go)
  4. 30GB EXT4 (64-bit Ubuntu-based Linux distro)

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