I have Ubuntu installed in an external device (GPT) in Legacy mode. I could run this Ubuntu in my old Windows 7 laptop. Now I have changed to a Windows 10 laptop in UEFI mode and I can't run ubuntu unless I enable Legacy mode.

So my problem is that I want to change Ubuntu to UEFI mode without reinstalling. When I run Boot-Repair, a message pops up saying:

The current session is in Legacy mode. Please reboot the computer, and use this software in an EFI session.

But I can't open Ubuntu if the legacy mode is disabled!

Is there any solution?

Edit: Solution

  1. Create a EFI partition
  2. As Melebius pointed out, Install Boot-repair in a flash usb
  3. Boot the flash usb in UEFI mode and follow the instructions.
  • Do you run Boot-Repair using a live medium or from your main Ubuntu installation? – Melebius Aug 20 '18 at 9:11
  • From main Installation. I have tried also from a second ubuntu installation (not live session) as posted in this question: askubuntu.com/questions/1067056/… – lsmor Aug 20 '18 at 11:58
  • UEFI's default is gpt partitioning. Did you use gpt on external drive. Most legacy installs are BIOS/MBR. You can convert drive in place from MBR to gpt but may be able to boot using MBR with UEFI. But will need an ESP - efi system partition. Not sure how to create with MBR but it must be FAT32 with boot flag. rodsbooks.com/gdisk/mbr2gpt.html But external drives only boot from /EFI/Boot/bootx64.efi. I typically copy /EFI/ubuntu twice to external and second copy is to /EFI/Boot and then I rename shimx64.efi to bootx64.efi. – oldfred Aug 20 '18 at 14:52

As the error message says, you should run Boot-Repair in UEFI mode. Since your main installation does not support that, you have to get a system where it’s possible. Moreover, modifying important properties of the running installations (like moving the root partition) is mostly not possible.

The easiest way is to run Boot-Repair from Ubuntu live medium or even using the Boot-Repair-Disk. Make sure to boot it in UEFI mode, the particular procedure depends on your hardware (or firmware to be precise).

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