I have a hard drive with Windows 10 on it and a spare one I installed Ubuntu on. I wanted to have it automatically boot the hard drive with Windows 10 on it instead of showing a grub menu and having to select what OS to boot into and then if I wanted to use the Ubuntu drive, I could just hit Esc key when my computer boots and select the Ubuntu drive and then have the grub menu pop up. Now when I select my Windows hard drive to boot it, it brings up grub rescue prompt but if I select the Ubuntu drive it brings up the grub menu to select the OS. I unplugged the Windows 10 hard drive when I installed Ubuntu so why is it being affected by the Ubuntu install when I try to boot that hard drive?
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Are both WIndows & Ubuntu in UEFI boot mode or both in BIOS boot mode. I sounds like you may have installed grub in BIOS mode on Windows drive. But if Windows is UEFI then it really boots from ESP - efi system partition. So can you select Windows and directly boot it from UEFI boot tab or one time boot key? – oldfred Aug 20 '15 at 03:30
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They're both BIOS, I'm running an older x58 mobo with an i7 920. I installed Ubuntu on a separate hard drive while disconnecting my other hard drives, one that has Windows 10 on it and the other two are storage drives for my Windows OS. I'm new to Linux so I just installed it from the CD and allowed it to create the partition scheme but I figured since it was on a separate hard drive from my Windows install, it would let me choose whatever drive through the BIOS and just load either Windows bootloader or GRUB. Now though if I try to boot the Windows drive it's stuck on grub rescue. – mut- Aug 20 '15 at 03:42
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I even deleted and reinstalled Windows 10 and disconnected all the other hard drives and it's still bringing up the grub rescue menu, how is that possible? Where is the information still being stored for GRUB, in my RAM or somewhere else? – mut- Aug 20 '15 at 03:45
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I think GRUB is installed in the Master Boot Record. – Buck Aug 20 '15 at 09:59
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Grub2's default install is to the drive seen as sda, often your Windows drive. You want Windows boot loader in MBR of Windows drive and grub in MBR of Ubuntu drive. Then normally boot from BIOS with grub as you can boot either system, but anytime can directly boot Windows drive from BIOS or one time boot key. Windows' fixMBR command should overwrite grub in MBR. Or use Boot-Repair. You may have to also install grub to MBR of UBuntu drive if not already there. – oldfred Aug 20 '15 at 21:55
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1Possible duplicate of Unable to boot into Windows after installing Ubuntu, how to fix? and How do I change the GRUB boot order? – karel Nov 13 '17 at 05:55
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I just set this up for my Dell laptop. I installed Ubuntu 14.04 LTS (not live) on a USB flash drive. When I boot my laptop, it boots to Windows 10 by default. Then, when I plug in the U-14 flash drive, I press F12 for the boot menu and choose Ubuntu.
In the computer BIOS, I turned OFF secure boot. I set Boot Options to Ubuntu, Windows Boot Manager, none and none.
Then I plugged in the Live and target USBs and booted to the Live USB. I used Gparted to partition a 2GB swap partition at the end of the target drive and formated the rest of the drive as EXT4, /. After applying the changes, I changed the flag of the main partition to boot.
When I chose the partitions to install I chose to install U14 to the / partition. I also changed the Boot option to SDB (not a partition.)
When I was done, I booted to the BIOS and turned ON the security boot.
When I boot, I press the F12 key and get a choice to boot to Windows or Ubuntu. If I remove the USB, it default boots to Windows.
I can also change the BIOS boot order to Ubuntu and then Windows. Once set, I can boot to Ubuntu as long as the flash drive is plugged in before I turn on the computer. But if I boot without it, I will have to use the boot menu to boot to Ubuntu until I change the BIOS default order again.
Ubuntu always boots through the Grub menu. Windows does not use the Grub menu.
I hope this helps.
