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I have a linux box (Ubuntu 16.04) whose boot disk is partitioned using MBR. How can I convert it to GPT+UEFI?

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Before starting, make sure you have a backup, and make sure to have a linux live boot ready to rescue your system. It's easy to mess this up!

  1. Use gdisk to convert the partition table to GPT.

    gdisk /dev/sda

  2. Create the "BIOS boot" partition that GRUB needs.

    n to create a new partition. Needs to be about 1MB. You can probably squeeze this in from sectors 34-2047. Use L or l to look up the code for "BIOS boot" (ef02).

  3. Write the new partition table.

    w

  4. Reload the partition table.

    partprobe /dev/sda

  5. Re-install the GRUB boot loader using the new partition scheme.

    grub-install /dev/sda

    Optionally reboot to verify it's working. If you just need GPT and not UEFI, you can stop here.

  6. Use gdisk to add an "EFI System" partition (ESP). Officially should be 100-500MB, but mine only used 130kB. Can be anywhere on the disk, so consider putting it at the end if you're using non-resizable media like a physical disk.

    gdisk /dev/sda and use n to create the partition.

  7. Give the ESP a distinctive label without whitespace like EFI-system, because we'll reference the partition label in fstab.

    c to set the label.

  8. Write the partition table.

    w

  9. Reload the partition table.

    partprobe /dev/sda

  10. Build the filesystem for the ESP.

    mkfs -t vfat -v /dev/disk/by-partlabel/EFI-system

  11. Create the ESP mount point.

    mkdir /boot/efi

  12. Add the ESP to /etc/fstab. It should look like this:

    /dev/disk/by-partlabel/EFI-system /boot/efi vfat defaults 0 2

  13. Mount the ESP.

    mount /boot/efi

  14. Install the GRUB EFI bootloader.

    grub-install --target=x86_64-efi /dev/sda

  15. Reboot.
  16. Change the BIOS from BIOS boot to UEFI boot.
  17. Use the one-time boot menu to force boot the disk. You may have to navigate to the disk -> EFI -> ubuntu -> grubx64.efi.
  18. Re-install GRUB's EFI bootloader to update the UEFI boot selector.

    grub-install

Resources:

  • The BIOS boot partition is only needed for doing legacy boot on a GPT partitioned disk. If you boot with UEFI, it is not needed and will not be used. – Michael Hampton Apr 16 at 1:40
  • You may also have to change your firmware settings to support UEFI booting. – fpmurphy Apr 26 at 19:40

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