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$FreeBSD: stable/11/stand/i386/gptboot/gptboot.8 347705 2019-05-16 15:32:03Z ian $
.Dd April 30, 2019 .Dt GPTBOOT 8 .Os .Sh NAME .Nm gptboot .Nd GPT bootcode for UFS on BIOS-based computers .Sh DESCRIPTION .Nm is used on BIOS-based computers to boot from a UFS partition on a GPT-partitioned disk. .Nm is installed in a .Cm freebsd-boot partition with .Xr gpart 8 .
p When it starts, .Nm first reads the GPT and determines which drive and partition to boot from, as described under .Sx BOOTING , below. If it does not find an eligible partition, or if the user hits a key within three seconds, .Nm switches from auto-boot to interactive mode. Interactive mode allows manual selection of the disk, partition, filename, and boot option flags, as described in .Xr boot 8 . .Sh IMPLEMENTATION NOTES The GPT standard allows a variable number of partitions, but .Nm only boots from tables with 128 partitions or less. .Sh PARTITION ATTRIBUTES .Nm checks and manages several attributes of GPT UFS partitions. l -tag -width ".Cm bootfailed" t Cm bootme Attempt to boot from this partition. If more than one partition has the .Cm bootme attribute set, .Nm will attempt to boot each one until successful. t Cm bootonce Attempt to boot from this partition only one time. Setting this attribute with .Xr gpart 8 automatically also sets the .Cm bootme attribute. Multiple partitions may have the .Cm bootonce and .Cm bootme attributes set. t Cm bootfailed The .Cm bootfailed attribute marks partitions that had the .Cm bootonce attribute set, but failed to boot. This attribute is managed by the system. See .Sx "BOOTING" and .Sx "POST-BOOT ACTIONS" below for details. .El .Sh USAGE For normal usage, the user does not have to set or manage any of the partition attributes. .Nm will boot from the first UFS partition found.
p The .Cm 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 .Cm 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 .Cm bootme attributes so the test partition becomes the new system partition. Because the .Cm 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 .Cm bootme attribute is set on any partitions, booting will be attempted from them first. If no partitions with .Cm bootme attributes are found, booting will be attempted from the first UFS partition found. .Sh BOOTING .Nm first reads the partition table. All .Cm freebsd-ufs partitions with only the .Cm bootonce attribute set, indicating a failed boot, are set to .Cm bootfailed . .Nm then scans through all of the .Cm freebsd-ufs partitions. Boot behavior depends on the combination of .Cm bootme and .Cm bootonce attributes set on those partitions. l -tag -width ".Cm bootonce + .Cm bootme" t Cm bootonce + Cm bootme Highest priority: booting is attempted from each of the .Cm freebsd-ufs partitions with both of these attributes. On each partition, the .Cm bootme attribute is removed and the boot attempted. t Cm bootme Middle priority: booting is attempted from each of the .Cm freebsd-ufs partitions with the .Cm bootme attribute. .El
p If neither .Cm bootonce nor .Cm bootme attributes are found on any partitions, booting is attempted from the first .Cm freebsd-ufs partition on the disk. .Sh POST-BOOT ACTIONS The startup script
a /etc/rc.d/gptboot checks the attributes of .Cm freebsd-ufs partitions on all GPT disks. Partitions with the .Cm bootfailed attribute generate a .Dq boot from X failed system log message. Partitions with only the .Cm bootonce attribute, indicating a partition that successfully booted, generate a .Dq boot from X succeeded system log message. The .Cm bootfailed attributes are cleared from all the partitions. The .Cm bootonce attribute is cleared from the partition that successfully booted. There is normally only one of these. .Sh FILES l -tag -width /boot/gptboot -compact t Pa /boot/gptboot bootcode binary t Pa /boot.config parameters for the boot blocks
q optional .El .Sh EXAMPLES .Nm is installed in a .Cm freebsd-boot partition, usually the first partition on the disk. A .Dq protective MBR
o see .Xr gpart 8
c is typically installed in combination with .Nm .
p Install .Nm on the
a ada0 drive: d -literal -offset indent gpart bootcode -b /boot/pmbr -p /boot/gptboot -i 1 ada0 .Ed
p .Nm can also be installed without the PMBR: d -literal -offset indent gpart bootcode -p /boot/gptboot -i 1 ada0 .Ed
p Set the .Cm bootme attribute for partition 2: d -literal -offset indent gpart set -a bootme -i 2 ada0 .Ed
p Set the .Cm bootonce attribute for partition 2, automatically also setting the .Cm bootme attribute: d -literal -offset indent gpart set -a bootonce -i 2 ada0 .Ed .Sh SEE ALSO .Xr boot.config 5 , .Xr rc.conf 5 , .Xr boot 8 , .Xr gpart 8 .Sh HISTORY .Nm appeared in FreeBSD 7.1. .Sh AUTHORS This manual page written by .An Warren Block Aq wblock@FreeBSD.org .