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Old 9th September 2017, 12:19 PM
owl102 Offline
Registered User
Join Date: Aug 2011
Location: Germany
Posts: 49
Re: Boot Windows 10 in Legacy Mode

Originally Posted by mac25 View Post
I installed Fedora 26 from USB on a laptop winth Windows 10 already installed (I assume in UEFI Mode) after disabling UEFI from the BIOS menu and booting in Legacy Mode.
I followed the instructions and installed GRUB2.
After I rebboted into Fedora, I edited /etc/grub.d/40_custom to include the following entry:

menuentry "Windows 10" --class windows --class os {
insmod ntfs
search --no-floppy --set=root --fs-uuid 5E64165E6416396B
ntldr /bootmgr

When I reboot, Windows 10 appears in the GRUB menu but when I choose it I get this error message:

file /bootmgr not found

How should I proceed to boot Windows 10 with GRUB?
If Windows is installed in UEFI mode, it's bound to UEFI and GPT partitioning. If Windows is installed in Legacy/CSM mode, it's bound to Legacy/CSM and MBR partitioning.

So in short, you cannot. If Windows is installed in UEFI mode, you have to boot it in UEFI mode, by either using the UEFI boot manager your PC offers, or by using a boot manager (like Grub) installed in UEFI mode.

As result, if you do not want to use the UEFI boot manager of your PC but Grub instead to offer a Windows boot parallel to Fedora boot, you have to install Fedora in UEFI mode as well.
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