Dual Boot on Separate Hard Disk Drives

[Shadius]

Hi Ubuntu Community,

I'd like to dual boot my existing Ubuntu OS with my existing Windows 10 OS. I have my Ubuntu installed on an HDD and my Windows 10 on an SSD.

How can I accomplish this dual boot setup where I have these two operating systems on their own drives?

[oldfred]

What is issue?
You say you already have them installed on separate drives? Or which is system is already installed?

Is system UEFI or old BIOS. And is Windows in UEFI or BIOS boot mode?

Generally easier to disconnect or in UEFI/BIOS settings disable Windows drive and install Ubuntu or vice-versa.

For UEFI install info see link in my signature below.

[Shadius]

Hi oldfred,

I do have them installed on their own drives, but I'd like to be able to select which OS to boot into.

The system is UEFI. How can I tell if Windows is in UEFI or BIOS boot mode?

[tea for one]

When you power on your PC, there should be a vendor screen with information to press a certain Function key to either access the System Set Up or Boot Device.

For example, I press

F10 for Boot Device
F2 for UEFI System Set Up

You will need to find the correct keys for your PC/Laptop.

Anyway, once you have established which key to press for Boot Device, you should then be able to select which drive to boot.

[tea for one]

The system is UEFI. How can I tell if Windows is in UEFI or BIOS boot mode?

When you are in Windows 10:-

System Information > System Summary > BIOS Mode (probably UEFI for Windows 10)

[oldfred]

In Ubuntu:
Query to check if UEFI or BIOS
[ -d /sys/firmware/efi ] && echo "EFI boot on HDD" || echo "Legacy boot on HDD"

You need to have both systems in same boot mode, to be able to use grub to dual boot or both as UEFI. But Window fast start up must also be off.

[Shadius]

Hi,

I may be a bit confused.

Instead of selecting the boot device to boot from by pressing DEL or F2 when my computer boots up, is there a way I can select the OS I want to boot into from a GRUB menu?

I want Windows as my primary OS and Ubuntu as my secondary OS.

[ubfan1]

You can set it up so you select Windows or Ubuntu from grub, but only if they have been installed in the same mode. You can adjust which OS is first (and default) to boot by renaming the files in /etc/grub.d/... to put the Windows script (30_os-prober?) before the Ubuntu script (10_linux). So something like mv 30_os-prober 05_os-prober should do it. Another easy way to check the Windows mode, look at the partition type of the disk, if the type is gpt, Windows is in UEFI mode.

[Shadius]

In Ubuntu:
Query to check if UEFI or BIOS
[ -d /sys/firmware/efi ] && echo "EFI boot on HDD" || echo "Legacy boot on HDD"

You need to have both systems in same boot mode, to be able to use grub to dual boot or both as UEFI. But Window fast start up must also be off.

Here's my output of the command:

shadius@shadius-phantom:~$ [ -d /sys/firmware/efi ] && echo "EFI boot on HDD" || echo "Legacy boot on HDD"
Legacy boot on HDD
shadius@shadius-phantom:~$

[oldfred]

Pre-installed Windows since Windows 8 released in 2012 is UEFI with gpt partitioning.
Windows only installs in UEFI boot mode to gpt partitioned drives.

Both Windows and Ubuntu can be installed by a user in the old BIOS/MBR configuration.
But UEFI & BIOS are not compatible. Once you start booting in one mode you cannot switch to other mode, or grub can only boot other installs in same boot mode.

If you used or have gpt partitioning on Ubuntu drive with an ESP - efi system partition (FAT32 with boot flag and at least 250MB) you can just reinstall grub when you boot live installer in UEFI mode. Easier with Boot-Repair. Otherwise, you need good backup of /home, perhaps /etc if you changed system settings, and list of installed applications to make it easy to reinstall them and then reinstall in UEFI boot mode.

Most suggest disconnecting Windows drive as Ubuntu's Ubiquity only installs grub to ESP on first drive, usually the windows drive. Most newer UEFI systems let you logically disconnect with UEFI drive settings and changing to disabled. Otherwise see this bug for workaround.

Posted work around to manually unmount & mount correct ESP during install #23 & #26
https://bugs.launchpad.net/ubuntu/+s...y/+bug/1396379

Or you can use Boot-Repair to reinstall grub after install. Grub installs to any drive, it is just Ubiquity that only installs to one drive, even though installer has options (that do not work in UEFI mode). Other distributions using grub2 let you choose drive and they work.

Shows first boot screen, so you know whether you have booted withUEFI or BIOS, although the choice in UEFI boot of flash drive usually says UEFI:XXXX for UEFI boot.
Shows installer with screen shots. Both BIOS purple accessibility screen & UEFI black grub menu screen
https://help.ubuntu.com/community/UEFI