Running on Hardware

To run on real hardware you'll need a specially-prepared USB drive.

Preparation

The general steps to prepare the drive are:

  1. Partition the drive using GPT.
  2. Create a partition.
  3. Set the partition type GUID to C12A7328-F81F-11D2-BA4B-00A0C93EC93B. That marks it as an EFI System partition. (On many UEFI implementations this is not strictly necessary, see note below.)
  4. Format the partition as FAT.
  5. Mount the partition.
  6. Create the directory path EFI/BOOT on the partition. (FAT is case insensitive, so capitalization doesn't matter.)
  7. Copy your EFI application to a file under EFI/BOOT. The file name is specific to the architecture. For example, on x86_64 the file name must be BOOTX64.EFI. See the boot files table for other architectures.

The details of exactly how to do these steps will vary depending on your OS.

Note that most UEFI implementations do not strictly require GPT partitioning or the EFI System partition GUID; they will look for any FAT partition with the appropriate directory structure. This is not required however; the UEFI Specification says "UEFI implementations may allow the use of conforming FAT partitions which do not use the ESP GUID."

Example on Linux

Warning: these operations are destructive! Do not run these commands on a disk if you care about the data it contains.

# Create the GPT, create a 9MB partition starting at 1MB, and set the
# partition type to EFI System.
sgdisk \
    --clear \
    --new=1:1M:10M \
    --typecode=1:C12A7328-F81F-11D2-BA4B-00A0C93EC93B \
    /path/to/disk

# Format the partition as FAT.
mkfs.fat /path/to/disk_partition

# Mount the partition.
mkdir esp
mount /path/to/disk_partition esp

# Create the boot directory.
mkdir esp/EFI/BOOT

# Copy in the boot executable.
cp /path/to/your-executable.efi esp/EFI/BOOT/BOOTX64.EFI

Booting the USB

Insert the USB into the target computer. Reboot the machine, then press the one-time boot key. Which key to press depends on the vendor. For example, Dell uses F12, HP uses F9, and on Macs you hold down the Option key.

Once the one-time boot menu appears, select your USB drive and press enter.