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I'm trying to troubleshoot why I can't boot to Windows.

The relevant entry in grub.cfg is:

### BEGIN /etc/grub.d/30_os-prober ###
menuentry 'Windows Boot Manager (on /dev/sda3)' --class windows --class os $menuentry_id_option 'osprober-efi-BC6E-0415' {
        insmod part_gpt
        insmod fat
        set root='hd0,gpt3'
        if [ x$feature_platform_search_hint = xy ]; then
          search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt3 --hint-efi=hd0,gpt3 --hint-baremetal=ahci0,gpt3  BC6E-0415
        else
          search --no-floppy --fs-uuid --set=root BC6E-0415
        fi
        chainloader /efi/Microsoft/Boot/bootmgfw.efi
}

Best I can tell, everything here is correct: /dev/disk/by-uuid/BC6E-0415 is indeed the Windows boot manager partition.

However I'm slightly confused by the references to (hd0,gpt3) because that's a completely different partition on a completely different physical disk. hd0 is the disk on which grub is installed though, in case that's relevant.

The actual error I get when I try and boot Windows is:

error: no such device: BC6E-0415
error: file `/efi/Microsoft/Boot/bootmgfw.efi' not found

I do notice that in grub, if I drop to a grub command prompt and do an ls, the only hard disk I see listed is hd0 when my system actually has 4 hard disks. As I mentioned above, hd0 is the hard disk that has grub and my Linux installs.

So I think my question might be: why, when I boot to grub, can't grub see any hard disks besides the one grub is on?

If I boot into Linux (Ubuntu 20.04.1) I can see all my hard disks just fine.

Update1: Boot Repair Output

As @oldfred suggested, output from boot-repair is here:

https://paste.ubuntu.com/p/MVKQGf76ZT/

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  • Lets see details, use ppa version with your live installer (2nd option) or any working install, not older Boot-Repair ISO: Please copy & paste the pastebin link to the Boot-info summary report ( do not post report), do not run the auto fix till reviewed. help.ubuntu.com/community/Boot-Repair & sourceforge.net/p/boot-repair/home/Home
    – oldfred
    Aug 29, 2020 at 18:37
  • Thanks @oldfred - post updated to include link to paste.
    – Bridgey
    Aug 29, 2020 at 18:58
  • Looks good to me. But grub only boots working Windows. Or Windows that is not hibernation nor needs chkdsk. And Windows fast start up turns on hibernation flag. Windows also regularly turns fast start up back on with updates, which you may not always even see. askubuntu.com/questions/843153/… & askubuntu.com/questions/145902/… You also only show two drives, not 4. If you plug in additional drives they may change drive order.
    – oldfred
    Aug 29, 2020 at 19:49
  • Thanks for looking @oldfred - as you can see from my answer, you from 2016 helped :) And you are right that the paste doesn't show four drives, only three: sda, sdb and nvme0n1 - I had unplugged the 4th a little while back while messing with something else.
    – Bridgey
    Aug 30, 2020 at 7:47

1 Answer 1

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The giveaway here was:

I do notice that in grub, if I drop to a grub command prompt and do an ls, the only hard disk I see listed is hd0 when my system actually has 4 hard disks. As I mentioned above, hd0 is the hard disk that has grub and my Linux installs.

And wonderfully. @oldfred from the past helped me fix it :)

As discussed in this thread, the problem was that the "Fast Boot" setting in my UEFI BIOS was set to initialise only the boot device. Consequently, the other devices (such as /dev/sda3) were not available to grub.

By changing the Fast Boot setting to 'hard drives only' all hard drives became available to grub.

I could see all hard drives by running ls within grub and can now boot to Windows.

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