In the Grub menu, Ubuntu boots ok but the Win10 selection receives the following error: Premature end of file /EFI/Microsoft/Boot/bootmgfw.efi

Grub works fine on several other of my dual boot machines - but the HP Laptop is UEFI rather than BIOS. The directory of:

/boot/efi/EFI/Microsoft/Boot/ has both the bootmgfw.efi AND the grubx64.efi files in it. I've tried removing the bootmgfw.efi file (backed up to a level down) but that doesn't work either.

Is there a way to edit the grub file so it does not find a "premature end" with the bootmgfw.efi file - or is there a better way?

Hey loftus49 - it sounds more like there is an integrity problem with the file instead of the file's actual presence or the GRUB configuration being the problem. The bootmgfw.efi file is the "stub" that your boot manager is looking to use to boot Windows - the error message seems to indicate some kind of corruption.

If this is the case, it is likely to be the type of problem requiring you to boot into your Windows installation media or recovery partition. There are tools there to troubleshoot and repair Windows booting problems. Successful repair using such methods will almost certainly result in your computer booting straight into Windows, not GRUB.

Thereafter, if you wish to restore dual-boot functionality, I have had much success with the Boot-Repair utility, available as a live ISO.

Please feel free to ask if more info is required.