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.\" $FreeBSD$
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.Dd January 25, 2018
.Dt UEFI 8
.Os
.Sh NAME
.Nm UEFI
.Nd Unified Extensible Firmware Interface bootstrapping procedures
.Sh DESCRIPTION
The
.Nm
Unified Extensible Firmware Interface provides boot- and run-time services
to operating systems.
.Nm
is a replacement for the legacy BIOS on the i386 and amd64 CPU architectures,
and is also used on arm, arm64 and ia64.
.Pp
The UEFI specification is the successor to the Extensible Firmware Interface
(EFI) specification.
The terms are often used interchangeably.
.Pp
The
.Nm
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
.Xr msdosfs 5
FAT file system with a specified file hierarchy.
.Bl -column -offset indent ".Sy Partition Scheme" ".Sy ESP Identifier"
.It Sy "Partition Scheme" Ta Sy "ESP Identifier"
.It GPT Ta C12A7328-F81F-11D2-BA4B-00A0C93EC93B
.It MBR Ta 0xEF
.El
.Pp
The
.Nm
boot process proceeds as follows:
.Bl -enum -offset indent -compact
.It
.Nm
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.
.Bl -column -offset indent "Architecture" "Default Path"
.It Sy Architecture Ta Sy Default Path
.It amd64 Ta Pa /EFI/BOOT/BOOTX64.EFI
.It arm64 Ta Pa /EFI/BOOT/BOOTAA64.EFI
.El
.Pp
The default
.Nm
boot configuration for
.Fx
installs
.Pa boot1.efi
in the default path.
.It
.Pa boot1.efi
reads boot configuration from
.Pa /boot.config
or
.Pa /boot/config .
Unlike other first-stage boot loaders,
.Pa boot1.efi
passes the configuration to the next stage boot loader and does not
itself act on the contents of the file.
.It
.Pa boot1.efi
searches partitions of type
.Li freebsd-ufs
and
.Li freebsd-zfs
for
.Pa loader.efi .
The search begins with partitions on the device from which
.Pa boot1.efi
was loaded, and continues with other available partitions.
If both
.Li freebsd-ufs
and
.Li freebsd-zfs
partitions exist on the same device the
.Li freebsd-zfs
partition is preferred.
.Pa boot1.efi
then loads and executes
.Pa loader.efi .
.It
.Pa loader.efi
loads and boots the kernel, as described in
.Xr loader 8 .
.El
.Pp
The
.Xr vt 4
system console is automatically selected when booting via
.Nm .
.Sh FILES
.Bl -tag -width /boot/loader -compact
.It Pa /boot/boot1.efi
First stage
.Nm
bootstrap
.It Pa /boot/boot1.efifat
.Xr msdosfs 5
FAT file system image containing
.Pa boot1.efi
for use by
.Xr bsdinstall 8
and the
.Ar bootcode
argument to
.Xr gpart 8 .
.It Pa /boot/loader.efi
Final stage bootstrap
.It Pa /boot/kernel/kernel
default kernel
.It Pa /boot/kernel.old/kernel
typical non-default kernel (optional)
.El
.Sh SEE ALSO
.Xr vt 4 ,
.Xr boot.config 5 ,
.Xr msdosfs 5 ,
.Xr boot 8 ,
.Xr efibootmgr 8 ,
.Xr efidp 8 ,
.Xr efivar 8 ,
.Xr gpart 8 ,
.Xr uefisign 8
.Sh HISTORY
EFI boot support for the ia64 architecture first appeared in
.Fx 5.0 .
.Nm
boot support for amd64 first appeared in
.Fx 10.1
and for arm64 in
.Fx 11.0 .
.Sh CAVEATS
EFI environment variables are not supported by
.Xr loader 8
or the kernel.