NAME
gptboot
—
GPT bootcode for UFS on BIOS-based
computers
DESCRIPTION
gptboot
is used on BIOS-based computers to
boot from a UFS partition on a GPT-partitioned disk.
gptboot
is installed in a
freebsd-boot
partition with
gpart(8).
When it starts, gptboot
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, or if the user hits a key within three seconds,
gptboot
switches from auto-boot to interactive mode.
Interactive mode allows manual selection of the disk, partition, filename,
and boot option flags, as described in
boot(8).
IMPLEMENTATION NOTES
The GPT standard allows a variable number of partitions, but
gptboot
only boots from tables with 128 partitions
or less.
PARTITION ATTRIBUTES
gptboot
checks and manages several
attributes of GPT UFS partitions.
bootme
- Attempt to boot from this partition. If more than one partition has the
bootme
attribute set,gptboot
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 thebootonce
andbootme
attributes set. bootfailed
- The
bootfailed
attribute marks partitions that had thebootonce
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
will boot from the
first UFS partition found.
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
first reads the partition table.
All freebsd-ufs
partitions with only the
bootonce
attribute set, indicating a failed boot,
are set to bootfailed
.
gptboot
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, thebootme
attribute is removed and the boot attempted. bootme
- Middle priority: booting is attempted from each of the
freebsd-ufs
partitions with thebootme
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
- bootcode binary
- /boot.config
- parameters for the boot blocks (optional)
EXAMPLES
gptboot
is installed in a
freebsd-boot
partition, usually the first partition
on the disk. A “protective MBR” (see
gpart(8)) is typically installed in combination with
gptboot
.
Install gptboot
on the
ada0 drive:
gpart bootcode -b /boot/pmbr -p /boot/gptboot -i 1 ada0
gptboot
can also be installed without the
PMBR:
gpart bootcode -p /boot/gptboot -i 1 ada0
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
HISTORY
gptboot
appeared in FreeBSD 7.1.
AUTHORS
This manual page written by Warren Block ⟨wblock@FreeBSD.org⟩.