Unable to dual-boot Qubes in Legacy mode

So I’ve been trying to add Qubes to my GRUB but it just can’t get it to work. What should I put in my 40_custom if I have a SSD? I am very disappointed as I really enjoyed using Qubes OS when I had it installed through UEFI. I then bought a new SSD specifically for Qubes, but then upon installation of the new SSD and the installation of Qubes onto the new SSD in Legacy mode, my GRUB dissappeared and my system would automatically boot into Ubuntu. I have never had this with any other OS, I always managed the find a solution after extensive troubleshooting.

This is my fdisk -l output:

Ubuntu is on the 256GB SSD, Qubes on the 1TB one. The HDD is empty.

Now I’ve tried about every option I’ve seen online and nothing works. I think my 40_custom entry is not correct. os-prober does not even show Qubes after mounting it…

I have literally spend 18 hours which is a lot for me, on the trying to fix this and am really at a loss. I have previously installed Qubes succesfully through UEFI, but the problem then was that I couldn’t boot into Ubuntu as it was a Legacy/UEFI mix.

You are not dual booting, there’s no need to configure grub. Change the boot order so your 1TB drive is booted first at your bios settings.

Not possible for me. In legacy mode I can only select one option that relates to a hard drive called “Hard Drive”. In UEFI I can select specific drives, but the problem is that Ubuntu is installed in legacy mode.

I think my question come down to:

  1. How to install Qubes OS
    1.1 Without installing in the same /boot/ as Ubuntu
    1.2 Without having to uninstall Ubuntu first
    1.3 Having installed Qubes OS after Ubuntu, how do I make sure the GRUB on Ubuntu can find the Qubes OS installation.

The reason for this is that I first want to become more proficient in Qubes before using it as my main driver. My files on Ubuntu right now are also way too important and I need to maintain easy access, at any moment I might need to access the files on there.

I am typing this from UEFI Qubes OS right now, if I want to go back to Ubuntu I need to:

  1. Reboot into BIOS
  2. Change from UEFI to Legacy
  3. Reboot into Ubuntu

Which is a pretty annoying process.

Yeah, that does sound pretty annoying.

Well, your machine needs a boot partition somewhere, and that partition needs to tell the machine where to go to continue the boot process (i.e. which drive to go to, where the .efi/.elf files are, kernel parameters, etc.)

Give this a try:

It would be whole lot simpler if your boot partition had configurations for Ubuntu and Qubes OS in it. Are you not wanting to do that for any particular reason?
(No judgement. Your machine, your rules. I just don’t want to give you advice that doesn’t fit your use case…)

If you don’t want to have a single boot partition containing config files for each OS, maybe have a first-port-of-call boot partition for your machine that simply says “go to the secondary boot partition”, and giving each installed OS its own dedicated boot partition as well?

Initial Boot Choices
Ubuntu / Qubes OS
/dev/sdb1 - Qubes OS Boot Partition -OR- /dev/sda2 - Ubuntu Boot Partition

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