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I've been trying to dual-boot Windows 10 with Ubuntu and facing a lot of challenges with the fact that Windows 10 automatically boots in UEFI mode, and not wanting to reinstall Windows to support Legacy Boot.

My Ubuntu installation was done in Legacy mode, so I've been following instructions in this link to convert the installation into UEFI mode. So far, I've been running into two problems:

1) When running Boot-Repair in Legacy mode, the GRUB Location menu is available, but unable to apply the fixes without booting in UEFI mode. 2) When running Boot-Repair in UEFI mode, the GRUB Location menu is wholly unavailable. The title "GRUB Location" is grayed out and no information is available inside of the tab.

I generated Boot Info with the Boot-Repair program, located here.

  • Why don't you install it properly in UEFI mode instead? It takes a lot less time than attempting a conversion that often fails. – user589808 Apr 29 '17 at 1:09
  • Installing in UEFI mode doesn't work like normal because Ubuntu installer doesn't recognize that Win10 is installed. – CannedSpinach Apr 29 '17 at 1:33
  • And that's a problem because...? help.ubuntu.com/community/UEFI – user589808 Apr 29 '17 at 1:34
  • I also tried following the instructions on that guide for installing as UEFI manually. It didn't work, just installed as Legacy instead. – CannedSpinach Apr 29 '17 at 1:49
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    Details on fast start up off: askubuntu.com/questions/843153/… You also managed to install the BIOS versions of grub to MBR and the FAT32 PBR. The install to MBR should not be an issue, but install to the ESP's PBR may be an issue. There may be a backup like with NTFS, do not even know. Even if it says good, as grub can be in a PBR, restore backup if good and available.help.ubuntu.com/community/BootSectorFix If not available, the backup entire ESP, sda2, delete it, create new FAT32 partition with boot flag to make it ESP & restore data. – oldfred Apr 29 '17 at 4:04
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The comments to your question may be helpful. Also, although it's been a while since I've used Boot Repair, it may simply not need the information on the "GRUB location" tab when run in EFI mode, so you could try it without entering that data. If you prefer to try something else, here's another way to do it:

  1. Disable Secure Boot. (See this page of mine for pointers on how to do this.)
  2. Download the USB flash drive or CD-R version of my rEFInd boot manager.
  3. Prepare a boot medium using the rEFInd image.
  4. Boot using the rEFInd medium. It should present options to boot both Windows and Ubuntu.
  5. Try both the Windows and Ubuntu boot options. If both work....
  6. Boot into Ubuntu.
  7. Mount your ESP (/dev/sda2) at /boot/efi (you may need to create this directory). You can do this temporarily with the mount command, but in the long run you may want to create an /etc/fstab entry for this, too.
  8. Install an EFI boot loader. Two options are likely to be relatively easy:
    • You can install the rEFInd Debian package or PPA to use rEFInd rather than GRUB as your default boot manager.
    • You can manually install GRUB by installing the grub-efi-amd64-signed package. You may also need to type sudo grub-install followed by sudo update-grub to fully install and configure it.
  9. Test that you can boot.
  10. You may optionally re-enable Secure Boot; however, if you installed rEFInd, you'll probably have to jump through some extra hoops, as described in the rEFInd Secure Boot documentation.
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    I followed all of the instructions in your post. The USB flash drive version of rEFInd failed to boot despite numerous attempts performed in a variety of different ways over the course of an hour. In addition, installing GRUB seemed pretty much entirely ineffective. I still feel woefully out of the loop on what's been causing all of these problems, but installing rEFInd through apt-get still somehow led me to be able to dual boot Win10 and Ubuntu in UEFI mode, so I owe you a big thank you. – CannedSpinach May 3 '17 at 23:39

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