I've just upgraded to Windows 10 from Windows 8.1 on my partitioned laptop that has Ubuntu 14.04 installed. Grub no longer appeared on boot so I ran boot-repair from an Ubuntu liveUSB. This didn't seem to have any effect. I've checked and secure boot is still disabled.
Log from boot-repair: http://paste.ubuntu.com/11972534/
So what's next?
Update: I've attempted to use chroot to update grub from my Ubuntu partition. update-grub runs successfully finding both linux and windows boot manager but the process still doesn't have any effect. grub-install complains that it cannot find EFI directory (but I have mounted everything correctly).
Update2: Just discovered that running efibootmgr after chroot into ubuntu shows ubuntu as not being in the boot order at all. I manually changed the order and rebooted to discover that the bootorder was reset. I run in windows: bcdedit /set {bootmgr} path \EFI\ubuntu\shimx64.efi But this has no effect either even after reporting 'Operation Successful'.
Best Answer
I just had to run this in Windows as an administrator:
Or, if you are using PowerShell:
GRUB appears fine on boot and I can boot into Ubuntu and Windows 10 fine.
As pointed out in the comments (by David Faure), the final argument to this command depends on your particular system configuration. You can use this command to determine the correct path for your system:
This will list all the installed boot managers and associated EFI paths, and grub should be somewhere in the list.