GPTBOOT.EFI(8) FreeBSD System Manager's Manual GPTBOOT.EFI(8)
NAME
gptboot.efi - GPT bootcode for UFS on UEFI computers
DESCRIPTION
gptboot.efi is used on UEFI computers to boot from a UFS partition on a
GPT-partitioned disk. gptboot.efi is installed in the EFI System
Partition (ESP). For BIOS-based computers, see gptboot(8) for details.
While conceptually similar, the details differ. gptboot.efi works only
with UFS root file systems. Users with ZFS partitions should use
loader.efi(8) with bectl(8) to control what dataset is used for root.
What UEFI computers boot is usually controlled via the mechanisms
explained in efibootmgr(8) using loader.efi(8) or boot1.efi(8). However,
some setups cannot use those mechanisms. When the users cannot rely on
host-supplied UEFI variables or they want the contents of the media alone
to decide root, gptboot.efi accomplishes these goals.
When it starts, gptboot.efi first reads the GPT and determines which
drive and partition to boot from, as described under BOOTING, below. If
it does not find an eligible partition, it returns to the UEFI firmware.
The firmware will then try the next bootable item in the UEFI Boot
Manager's list, if any, usually a different disk.
IMPLEMENTATION NOTES
The GPT standard allows a variable number of partitions, but gptboot.efi
only boots from tables with 128 partitions or less.
PARTITION ATTRIBUTES
gptboot.efi checks and manages several attributes of GPT UFS partitions.
These flags are FreeBSD specific and non-standard.
bootme Attempt to boot from this partition. If more than one
partition has the bootme attribute set, gptboot.efi will
attempt to boot each one until successful.
bootonce Attempt to boot from this partition only one time. Setting
this attribute with gpart(8) automatically also sets the
bootme attribute. Multiple partitions may have the bootonce
and bootme attributes set.
bootfailed The bootfailed attribute marks partitions that had the
bootonce attribute set, but failed to boot. This attribute
is managed by the system. See BOOTING and POST-BOOT ACTIONS
below for details.
USAGE
For normal usage, the user does not have to set or manage any of the
partition attributes. gptboot.efi will boot from the first UFS partition
found on the device.
The bootonce attribute can be used for testing an upgraded operating
system on an already-working computer. The existing system partition is
left untouched, and the new version of the operating system to be tested
is installed on another partition. The bootonce attribute is set on that
new test partition. The next boot is attempted from the test partition.
Success or failure will be shown in the system log files. After a
successful boot of the test partition, a user script can check the logs
and change the bootme attributes so the test partition becomes the new
system partition. Because the bootonce attribute is cleared after an
attempted boot, a failed boot will not leave the system attempting to
boot from a partition that will never succeed. Instead, the system will
boot from the older, known-working operating system that has not been
modified. If the bootme attribute is set on any partitions, booting will
be attempted from them first. If no partitions with bootme attributes
are found, booting will be attempted from the first UFS partition found.
BOOTING
gptboot.efi first reads the partition table. All freebsd-ufs partitions
with only the bootonce attribute set, indicating a failed boot, are set
to bootfailed. gptboot.efi then scans through all of the freebsd-ufs
partitions. Boot behavior depends on the combination of bootme and
bootonce attributes set on those partitions.
bootonce + bootme Highest priority: booting is attempted from each
of the freebsd-ufs partitions with both of these
attributes. On each partition, the bootme
attribute is removed and the boot attempted.
bootme Middle priority: booting is attempted from each of
the freebsd-ufs partitions with the bootme
attribute.
If neither bootonce nor bootme attributes are found on any partitions,
booting is attempted from the first freebsd-ufs partition on the disk.
POST-BOOT ACTIONS
The startup script /etc/rc.d/gptboot checks the attributes of freebsd-ufs
partitions on all GPT disks. Partitions with the bootfailed attribute
generate a "boot from X failed" system log message. Partitions with only
the bootonce attribute, indicating a partition that successfully booted,
generate a "boot from X succeeded" system log message. The bootfailed
attributes are cleared from all the partitions. The bootonce attribute
is cleared from the partition that successfully booted. There is
normally only one of these.
FILES
/boot/gptboot.efi bootcode binary
/boot/efi/efi/boot/bootx64.efi
Default boot loader for amd64 systems.
/boot/efi/efi/boot/bootaa64.efi
Default boot loader for arm64 systems.
/boot/efi/efi/boot/bootarm.efi
Default boot loader for arm systems.
/boot/efi/efi/boot/bootriscv64.efi
Default boot loader for riscv systems.
EXAMPLES
gptboot.efi is installed in the ESP with cp(1).
Install gptboot.efi into the ESP for the system. This assumes the ESP is
mounted in the standard /boot/efi directory. For amd64, use the
following
cp /boot/gptboot.efi /boot/efi/efi/boot/bootx64.efi
For other systems, use the file listed in the FILES section.
Set the bootme attribute for partition 2:
gpart set -a bootme -i 2 ada0
Set the bootonce attribute for partition 2, automatically also setting
the bootme attribute:
gpart set -a bootonce -i 2 ada0
SEE ALSO
rc.conf(5), boot(8), efibootmgr(8), gpart(8), gptboot(8), loader.efi(8)
HISTORY
gptboot.efi appeared in FreeBSD 13.0
AUTHORS
This manual page was written by Warner Losh <imp@FreeBSD.org>. It is
based heavily on the gptboot(8) man page by
Warren Block <wblock@FreeBSD.org>.
FreeBSD 15.1-STABLE-HBSD April 13, 2023 GPTBOOT.EFI(8)