I currently use a computer with one hard drive where Windows 10 is installed. I would like to put a second hard drive into my computer, with Ubuntu installed on it, and choose which OS I would like to boot when starting my computer. Ubuntu is already installed on the second hard drive, but is not in the computer yet.

My question is : Do I have to configure anything or can I just put the second hard drive in my computer, and when I will turn it on again my screen will ask me automatically in which drive I want to boot ?

  • 1
    If you don't have anything on the new disk except for your OS then you can install fresh. That is the way I tested it, but otherwise you can start from step 6 - it should work without any problem, you basically have to make sure that the bootloader lands on the efi partition of the primary drive (/dev/sda?) and then run grub-update: scriptsandoneliners.blogspot.com/2017/06/… – A.Danischewski Oct 8 '19 at 11:56
  • You just need to skip the install part in the instructions - if you can get Linux to boot off your external drive via Bios do that, otherwise use a Live Linux USB and do a chroot to your external hard drive. – A.Danischewski Oct 8 '19 at 12:07
  • 1
    Are both installed in UEFI boot mode or BIOS boot mode? They must be the same. If UEFI, you need to add an UEFI boot entry into UEFI for Ubuntu if internal drive. If external drive UEFI always boots from /EFI/Boot/bootx64.efi which should already exist. You can use efibootmgr to add UEFI boot entry or re-install grub which uses efibootmgr to add UEFI entry. Often easier to use Boot-Repair from Ubuntu live installer. help.ubuntu.com/community/Boot-Repair Efibootmgr examples: askubuntu.com/questions/668506/… – oldfred Oct 8 '19 at 15:43
  • The windows drive is in UEFI but I dont know for the other one – Alexis Pister Oct 8 '19 at 15:48
  • ... can I just put the second hard drive in my computer Maybe yes, maybe no. None of us knows if your PC has the room and connections for another drive, whether it's an old spinning Hard Disk Drive ('HDD') or the modern Solid State Drive ('SSD') which is much faster. Nor can we recommend which specifications for the second drive, whether SAS, SATA-II, SATA-III, NVMe/PCIe, M.2, M-SATA, or other standards. The make and model of the PC would be very helpful. Please click edit and tell us, in your question, the make and the model; get the model from the serial number sticker not other places. – K7AAY Oct 8 '19 at 19:01

Presuming that your external hard drive that you said has Ubuntu installed has data that you want to keep. I recommend you boot with Grub, this is how I dual boot Ubuntu on my Windows 10 laptop.

What you need to do is:

  1. Create a live Ubuntu USB stick
  2. Boot into Ubuntu on the live USB stick and configure networking
  3. Create a directory called /target on the live USB stick sudo mkdir /target
  4. Attach and mount your external hard drive on /target. If it auto mounts someplace else, just sudo umount /mnt/someplaceelse and mount it on /target.
    Eg. sudo mount /dev/sdb1 /target # If /dev/sdb1 is your external hard drives primary partition
  5. Make a directory on /target if it does not already exist called /boot/efi
    $> sudo mkdir -p /target/boot/efi
  6. Bind mount critical live USB directories onto /target:
    $> for a in /sys /proc /run /dev; do sudo mount --bind "$a" "/target${a}"; done
  7. Use gparted to determine the location of the efi partition on your windows hard drive
    $> sudo gparted /dev/sda # If /dev/sda is your windows hard drive
  8. Mount the Windows Boot Manager efi partition on /target/boot/efi:
    $> sudo mount /dev/sdXY /target/boot/efi
  9. Chroot to /target: $> sudo chroot /target
  10. On chroot:
    $> sudo apt-get update
    $> sudo apt-get install grub2
    $> sudo update-grub2
    $> exit
  11. Reboot: $> reboot
  12. While rebooting pull the USB thumbdrive out of your computer - you should be brought back into Ubuntu this time on the external hard drive (not the USB thumbdrive)
  13. Re-run an update of grub2:
    $> sudo apt-get update
    $> sudo update-grub2


Note: if you have trouble for any reason and you want to boot into Windows just hit escape and you should see the bootloader option screen and select Windows. If not just go into your Bios and change the boot load priority.


... when I will turn it on again my screen will ask me automatically in which drive I want to boot? Your PC will not automagically ask, and depending on your BIOS/firmware, the process to select the drive will vary. You will need to press whatever key is used for Boot Selection (F10 and F11 are common), then select the drive to boot from.

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