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I installed Ubuntu 15.10 on a 60GB SSD. Then, some weeks later, I installed Windows 10 on a separate 500GB HDD (Ubuntu deserves the SSD more than Windows!).

Basically, my problem is that neither of the OS's know of each other, and in order to select the OS on startup, I have to enter the BIOS and manually boot off one or the other. How can I use either the Windows Boot Manager or GRUB2 to select which one I want to boot, the way most dual-boot systems are set up?

P.S. Both OS's work perfectly fine (I unplugged the Ubuntu disk when I installed Windows 10) and nothing is broken.

  • Did you install both systems in UEFI boot mode or both system in BIOS boot mode. If mixed you can only dual boot from UEFI boot menu or one time boot key. Grub only boot systems installed in same boot mode. Or once you start booting in one mode you cannot change to other mode. – oldfred Dec 17 '15 at 4:58
  • Chances are the second (but not the first) of the commands specified by Daniel will fix the problem; however, oldfred raises an important question -- if you've accidentally created a mixed-mode install, neither the Windows boot loader nor GRUB will be able to boot the other OS. We'd need to see the output (RESULTS.txt file) from Boot Info Script to understand your setup well enough to offer advice in this situation. You can post that to a pastebin site and post the URL to your document here. – Rod Smith Dec 17 '15 at 14:23
  • Here is the output of that script: paste.ubuntu.com/14082069 For some reason, it is detection Windows on three different partitions, even though I only have one Windows installed. Thanks for the help! – willem.hill Dec 18 '15 at 0:42
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You have to update grub's config file:

sudo grub-mkconfig -o /boot/grub/grub.cfg

That should do the trick.

IF grub isn't installed on /dev/sda (or the primary boot device, whatever that is) then run:

sudo grub-install /dev/sda
  • Only the second of those commands (grub-mkconfig) is necessary. In fact, the first could create new problems -- if the system is booted in EFI mode or if Windows is on /dev/sda, the first command will either not work or will overwrite the Windows boot loader, which will render Windows unbootable. – Rod Smith Dec 17 '15 at 14:20

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