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I'm trying to install an Ubuntu Gnome 14.04 in dual boot with Windows 10 (already installed).

I've tried with a bootable USB drive and an USB DVD drive (my notebook has no optical drive), but every time a line of text flashes by:

Could not open EFI boot fallback.efi 14

and nothing happens.

There is no safe boot option in the BIOS, and according to system info, Windows 10 is in "legacy" mode and NOT in UEFI.

How should I proceed?

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  • What exactly do you want, you want to dual boot machine or rollback to previous successful boot or running state?
    – Chinmaya B
    Dec 6, 2015 at 20:30
  • @Creator: Could you please review my edits and also review the editing help to improve the readability of your own edits in the future... ;-)
    – Fabby
    Dec 6, 2015 at 20:40
  • @Fabby - can you specify my mistakes , I mean you just edited two or three words, and what makes my edits poor?
    – Chinmaya B
    Dec 6, 2015 at 20:44
  • @Creator: Where can you see the words "your edits are poor?" ;-) I'm just saying that I improved your improvements even more... You live and you learn... What I did was: 1. Correct CaPiTaLiSaTiOn, 2. Add an actual question. 3. Improved readability. :-)
    – Fabby
    Dec 6, 2015 at 20:50
  • @Fabby -Chill citizen of this galaxy. I am just asking what was more improvement in that question, which I missed.
    – Chinmaya B
    Dec 6, 2015 at 20:54

1 Answer 1

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First, the message Could not open EFI boot fallback.efi is produced by Shim, which is a Linux tool for handling Secure Boot. Shim tries to launch a series of follow-on programs, one of which is called fallback.efi. Ideally, Shim will launch GRUB, which is the default boot loader for Ubuntu. Either that's not happening for some reason or GRUB is being launched after Shim complains about the absence of fallback.efi and then GRUB is crashing. I'd need to dig through the Shim source code to verify the exact path it takes to figure out which is the more likely explanation.

One critical point is that Shim (and anything with a .efi filename extension) is an EFI program. Thus, this message indicates that your system was booting in EFI mode. If you're right about Windows being installed in BIOS/CSM/legacy mode, you do NOT want to install Ubuntu in EFI mode. Thus, you may want to investigate ways to force the system to boot in BIOS/CSM/legacy mode. OTOH, if the computer came installed with Windows 10 (or even with Windows 8.x, which you then upgraded to Windows 10), it's almost certainly booting in EFI mode, not in BIOS mode. You haven't specified the history of the computer, or even its make and model, so it's hard for me to judge this. Because ascertaining the current boot mode is so critical, I strongly recommend that you review this point. In Windows, boot mode is pretty tightly tied to partition table type. If it's booting in BIOS mode, the partition table type will be MBR (aka MS-DOS or various other things). If it's booting in EFI mode, the partition table type will be GPT. See here for more information.

If your Windows really is in BIOS mode, you need to boot the Ubuntu installer in the same mode. There are a couple of ways you can force this issue, although both have problems:

  • You can remove the EFI boot loaders from your boot medium. The boot loaders appear in the EFI/BOOT directory on the boot medium. Depending on how you prepared your USB flash drive, you can rename (or delete) that directory tree to ensure that the disk will be unbootable in EFI mode. With any luck, your computer will then drop back to BIOS-mode booting. This approach is obviously easier with a USB flash drive than with an optical disc, since the latter would require re-mastering to modify, and that's a tricky process for an Ubuntu installation disc.
  • You can select the correct boot mode in your firmware's boot manager. Chances are you used the boot manager to select the boot medium. If not, it's usually access by hitting Esc, Enter, or a function key (usually between F8 and F12) soon after powering on the computer. Most UEFI implementations present two boot options for external media, one of which includes the string "UEFI" and the other of which doesn't. Select the option that lacks the "UEFI" string to boot in BIOS/CSM/legacy mode.

Both of these approaches are based on the premise that the boot medium is bootable in BIOS mode. This is not guaranteed. Depending on how you prepared the disk, it's entirely possible that it will be missing the BIOS-mode boot loader. If that's the case, you'll need to create the disk from the downloaded .iso file again, but use a different program, or at least different options in the program, to get it to boot.

Going back to the earlier point about your Windows installation: If in fact you've got an EFI-mode Windows installation, things change. It could be that your disk was improperly prepared and is missing some critical EFI-mode boot files, in which case you might need to re-create the disk. Another possibility is that you're running into a Secure Boot problem, and disabling this firmware feature would help.

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