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Manual Pages  — UEFI

NAME

UEFI – Unified Extensible Firmware Interface bootstrapping procedures

CONTENTS

DESCRIPTION

The UEFI Unified Extensible Firmware Interface provides boot- and run-time services to operating systems. UEFI is a replacement for the legacy BIOS on the i386 and amd64 CPU architectures, and is also used on arm, arm64 and ia64.

The UEFI specification is the successor to the Extensible Firmware Interface (EFI) specification. The terms are often used interchangeably.

The UEFI boot process loads system bootstrap code located in an EFI System Partition (ESP). The ESP is a GPT or MBR partition with a specific identifier that contains an msdosfs(5) FAT file system with a specified file hierarchy.
Partition Scheme ESP Identifier

GPT
C12A7328-F81F-11D2-BA4B-00A0C93EC93B

MBR
0xEF

The UEFI boot process proceeds as follows:

  1. UEFI firmware runs at power up and searches for an OS loader in the EFI system partition. The path to the loader may be set by an EFI environment variable. If not set, an architecture-specific default is used.
    Architecture Default Path

    amd64
    /EFI/BOOT/BOOTX64.EFI

    arm64
    /EFI/BOOT/BOOTAA64.EFI

    The default UEFI boot configuration for FreeBSD installs boot1.efi in the default path.

  2. boot1.efi reads boot configuration from /boot.config or /boot/config. Unlike other first-stage boot loaders, boot1.efi passes the configuration to the next stage boot loader and does not itself act on the contents of the file.
  3. boot1.efi searches partitions of type freebsd-ufs and freebsd-zfs for loader.efi. The search begins with partitions on the device from which boot1.efi was loaded, and continues with other available partitions. If both freebsd-ufs and freebsd-zfs partitions exist on the same device the freebsd-zfs partition is preferred. boot1.efi then loads and executes loader.efi.
  4. loader.efi loads and boots the kernel, as described in loader(8).

The vt(4) system console is automatically selected when booting via UEFI.

FILES

/boot/boot1.efi
  First stage UEFI bootstrap
/boot/boot1.efifat
  msdosfs(5) FAT file system image containing boot1.efi for use by bsdinstall(8) and the bootcode argument to gpart(8).
/boot/loader.efi
  Final stage bootstrap
/boot/kernel/kernel
  default kernel
/boot/kernel.old/kernel
  typical non-default kernel (optional)

SEE ALSO

vt(4), boot.config(5), msdosfs(5), boot(8), efibootmgr(8), efidp(8), efivar(8), gpart(8), uefisign(8)

HISTORY

EFI boot support for the ia64 architecture first appeared in FreeBSD 5.0 . UEFI boot support for amd64 first appeared in FreeBSD 10.1 and for arm64 in FreeBSD 11.0 .

CAVEATS

EFI environment variables are not supported by loader(8) or the kernel.

UEFI (8) January 25, 2018

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