Table of Contents

  1. System info
  2. BIOS Steps
  3. OS Steps:
    1. (Linux)Step 1. Verify you are booted into UEFI mode
    2. Step 2. If not GPT , convert partition to MBR
  4. (windows) Convert disk to MBR
  5. Convert MBR → GPT in Linux (for Secure Boot)
    1. 1. Check if your disk is MBR
    2. 2. Install gdisk
    3. 3. Run gdisk on your disk
    4. 4. Convert with Recovery & Transformation menu
    5. 5. Create / Verify EFI System Partition
    6. 6. Reinstall GRUB in UEFI mode
    7. 7. Reboot & Enable Secure Boot

System info

BIOS Version: ASRock B650 PG Riptide Wifi 5G Linux Version: Ubuntu 24.04.3 LTS

Steps that are specific to windows will be labeled with “(windows)”

BIOS Steps

In bios settings:

  1. Boot -> CSM = off
  2. Advanced -> AMD fTPM Switch = amd cpu ftpm
  3. Security -> Secure Boot -> Secure Boot Mode = Custom
  4. Security -> Install Default Security Boot Keys
  5. Save changes & reboot
  6. Security -> Secure Boot = Enabled

OS Steps:

(Linux)Step 1. Verify you are booted into UEFI mode 

lsblk -o NAME,PTTYPE # partitions should show "gpt" 

ls /sys/firmware/efi # if folder is present / populated , then you have verified you are in UEFI mode

Step 2. If not GPT , convert partition to MBR

(windows) Convert disk to MBR

Run in admin command prompt

mbr2gpt /convert /allowfullos

Convert MBR → GPT in Linux (for Secure Boot)

Secure Boot requires UEFI boot mode + GPT partitioning. If your Linux disk uses MBR (msdos), you must convert it to GPT.

⚠️ Warning: Always back up important data. Partition table conversion is risky.

1. Check if your disk is MBR

Run:

lsblk -o NAME,PTTYPE
  • If it shows dos → MBR (needs conversion).
  • If it shows gpt → you’re already set.

2. Install gdisk 

# Debian/Ubuntu
sudo apt install gdisk

# Fedora/RHEL/Alma
sudo dnf install gdisk

3. Run gdisk on your disk

Replace /dev/sdX with your actual disk (not a partition):

sudo gdisk /dev/sdX

You’ll see a message like:

MBR detected! This disk has an MBR partition table.
Converted to GPT. This is a potentially destructive operation.

4. Convert with Recovery & Transformation menu

Inside gdisk:

r   # recovery & transformation menu
g   # convert MBR -> GPT
p   # print partition table to confirm
w   # write changes and exit

5. Create / Verify EFI System Partition

Check existing partitions:

lsblk -f
  • If /boot/efi already exists (FAT32) → good.
  • If not, create one (~100–500MB FAT32):
sudo parted /dev/sdX
(parted) mkpart primary fat32 1MiB 513MiB
(parted) set 1 esp on

Format it:

sudo mkfs.fat -F32 /dev/sdX1

Mount at /boot/efi.

6. Reinstall GRUB in UEFI mode 

# Debian/Ubuntu
sudo grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=GRUB
sudo update-grub

# Fedora/RHEL/Alma
sudo grub2-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=GRUB
sudo grub2-mkconfig -o /boot/grub2/grub.cfg

7. Reboot & Enable Secure Boot

  1. Reboot into BIOS
  2. Disable CSM
  3. Enable Secure Boot
  4. Install default Secure Boot keys if prompted

Your Linux should now boot in UEFI mode with Secure Boot available.