If you’re like me, dual boot Windows and Ubuntu on your computer, there is a high chance that your grub menu will disappear after updating to Windows 10. This is a huge disappointment, cause I have once praised Windows 8 for “not destroying grub”.
If using boot-repair or update-grub with Ubuntu Live CD doesn’t help, you could try the following:
You may just have to run the following command in Command Prompt on Windows with administrator privilege
bcdedit /set {bootmgr} path \EFI\ubuntu\grubx64.efi
I haven’t got how or why this happened (and how this can fix the problem), but give me a shout if it works for you.