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I have a dual boot Windows 8 and Ubuntu 16.04, my Windows is installed in UEFI, and installed Ubuntu, by mistake in legacy mode, now when I boot, it went straight to Ubuntu, does not see Windows, how do I solve this?
1) do I need to reinstall Windows?
2) preparing another Ubuntu USB bootable in UEFI mode and reinstalling Ubuntu will solve this problem (will the Ubuntu installed in UEFI mode sees the installed Windows?)
3) is there a safe way to make legacy installed Ubuntu into UEFI without reinstalling it?
3) just curious, Ubuntu bootable USB stick is the same for UEFI or legacy, it's just the BIOS install method differs, in other words, the same USB stick can be used for UEFI and legacy, it's just the install method chosen during installation that differs.

Michael
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  • "is there a safe way to make legacy installed Ubuntu into UEFI without reinstalling it?" Yes. Add the directory with contents of UEFI to the USB. – Rinzwind Jul 18 '19 at 10:04
  • https://askubuntu.com/questions/1073492/windows-10-in-uefi-mode-and-ubuntu-in-legacy-mode/1073683#1073683 – mook765 Jul 18 '19 at 10:34

1 Answers1

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Do I need to reinstall Windows?

No

preparing another Ubuntu USB bootable in UEFI mode and reinstalling Ubuntu will solve this problem (will the Ubuntu installed in UEFI mode sees the installed Windows?)

Yes, unless you make the mistake of deleting windows during installing. Do make backups of personal files ;)

is there a safe way to make legacy installed Ubuntu into UEFI without reinstalling it?

Technically yes.

just curious, Ubuntu bootable USB stick is the same for UEFI or legacy, it's just the BIOS install method differs, in other words, the same USB stick can be used for UEFI and legacy, it's just the install method chosen during installation that differs.

The difference between the installer being UEFI or legacy is the presence of 

/sys/firmware/efi/

on the installer. Remove it and it will boot legacy. Adding it should also be possible but you then need to find the correct files. But it will be easier to just recreate the installer. A method is described here: How to change ubuntu install from legacy to uefi

Rinzwind
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