I have installed Ubuntu alongside with Windows 10, and they are on different disks. Since the disk containing Windows does not have a UEFI partition and uses C:/EFI/Microsoft/Boot/bootmgfw.efi to load Windows instead, grub does not recognize the Windows bootloader.

If I boot from Ubuntu install USB and enter the grub command line, by running the following commands I can start Windows successfully:

chainloader (hd1,msdos1)/EFI/Microsoft/Boot/bootmgfw.efi

However, if I enter the grub command line of the installed Ubuntu on disk, when I run:

chainloader (hd1,msdos1)/EFI/Microsoft/Boot/bootmgfw.efi

it print Error: invalid signature. If I add --force option to chainloader and then boot, the screen goes blank and windows does not start up.

Can anyone give some suggestions on how to boot Windows from Ubuntu grub?

  • Post this sudo parted -l to confirm partitioning. But It looks like you have mixed UEFI & BIOS. UEFI & BIOS boot modes are not compatible. Or once you start booting in one mode, you cannot switch. If Windows is msdos (MBR) then it has to be in BIOS boot mode. Microsoft has required vendors to install in UEFI mode, but how you boot install media UEFI or old BIOS mode, is then how it installs. Grub in UEFI boot mode cannot boot BIOS Windows. Best to backup your data & reinstall Windows in UEFI mode.Wuindows requires gpt partitioning for UEFI and conversion from MBR to gpt will erase drive.
    – oldfred
    Sep 28 at 14:49

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