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

3 Answers 3


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.


  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.


  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 EFI package on Ubuntu/Debian.

    apt install grub-efi-amd64

  15. Install the GRUB EFI bootloader.

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

  16. Reboot.

  17. Change the BIOS from BIOS boot to UEFI boot.

  18. Use the one-time boot menu to force boot the disk. You may have to navigate to the disk (Boot from file) -> EFI -> ubuntu -> grubx64.efi.

  19. Re-install GRUB's EFI bootloader to update the UEFI boot selector.



  • 1
    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. Apr 16, 2019 at 1:40
  • You may also have to change your firmware settings to support UEFI booting.
    – fpmurphy
    Apr 26, 2019 at 19:40
  • 8
    It should be noted that maybe you should install grub-efi-amd64 package before you get started with this, otherwise you can end up in all sorts of tinkering with chroot in order to be able to install grub and boot (like I ended up)
    – jsaddwater
    Jan 23, 2020 at 20:00
  • Have a look at How to initialize new disk for UEFI/GPT? for additional hints. Do not apply its hybrid guide, though, since you will delete the existing partitions as soon as you go to geparted, choose "Device" --> GPT. That is why this gdisk is needed. Still the link might generally help understand what is going on between the lines. Dec 22, 2020 at 11:19

I was converting my BIOS/MBR system HDD to UEFI/GPT without data loss

I booted in BIOS legacy mode with MBR boot disc.

As said, I shrunk last partition to create space for new EFI System partition with gParted and formatted it to FAT32.

Then with gdisk addded this new partition and converted MBR boot disc to GPT, without data loss (two root and one home partition):

Number  Start (sector)    End (sector)  Size       Code  Name
1            2048        40003583   19.1 GiB    8300  Linux filesystem
2       956772352       976771071   9.5 GiB     8200  Linux swap
3        40003584       893857099   407.1 GiB   8300  Linux filesystem
4       894054400       956465151   29.8 GiB    8300  Linux filesystem
5       956465152       956772351   150.0 MiB   EF00  EFI System

I mounted this Partition as (without any fstab modifications):

 sudo  mount /dev/sda5  /boot/efi

And then installed GRUB-EFI:

 sudo grub-install --target=x86_64-efi --efi-directory=/boot/efi /dev/sda

I Booted with Legacy BIOS and of course didn't have efivars, so got errors...

But after i rebooted my PC to change BOOT mode to UEFI Native, I was puzzled that my PC booted normally... GRUB UEFI, despite EFI variables error, was installed OK

I executed grub-install again and this time it went OK.

  • Ubuntu ships the expected boot entry configuration in /boot/efi/EFI/ubuntu/BOOTX64.CSV which is written to NVRAM by shim's fallback if it's missing, so this is expected behaviour.
    – YtvwlD
    Mar 23, 2021 at 17:13

Sorry first of all, have not been here for some time and I can only "answer"? I want to ask a further question on the same topic. I am currently trying to convert everything to GPT/EUFI so I can use secure boot, so that I can upgrade my WIndows 10 to 11 finally (got new hardware). So, specifically, is there any order to convert first? Windows or Linux? I remember years ago when I installed this setup, I had to make sure to install Windows first. Also, what if they are on different drives? I have a setup with Ubuntu 22 and grub on sda, and Windows 10 on sdc (sdb is just an old storage drive) and everything is booting and running fine after my mobo/cpu/mem change but currently with secure boot disabled and legacy boot (csm or something it's called?) turned ON. I have this guide and one for Windows, but does it matter how or which order I do them? Thanks!

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