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Man Pages
ZFSBOOT(8) FreeBSD System Manager's Manual ZFSBOOT(8)

zfsboot
bootcode for ZFS on BIOS-based computers

zfsboot is used on BIOS-based computers to boot from a filesystem in a ZFS pool. zfsboot is installed in two parts on a disk or a partition used by a ZFS pool. The first part, a single-sector starter boot block, is installed at the beginning of the disk or partition. The second part, a main boot block, is installed at a special offset within the disk or partition. Both areas are reserved by the ZFS on-disk specification for boot use. If zfsboot is installed in a partition, then that partition should be made bootable using appropriate configuration and boot blocks described in boot(8).

The zfsboot boot process is very similar to that of gptzfsboot(8). One significant difference is that zfsboot does not currently support the GPT partitioning scheme. Thus only whole disks and MBR partitions, traditionally referred to as slices, are probed for ZFS disk labels. See the BUGS section in gptzfsboot(8) for some limitations of the MBR scheme support.

zfsboot supports all the same prompt and configuration file arguments as gptzfsboot(8).

/boot/zfsboot
boot code binary
/boot.config
parameters for the boot block (optional)
/boot/config
alternative parameters for the boot block (optional)

zfsboot is typically installed using dd(1). To install zfsboot on the ada0 drive:
dd if=/boot/zfsboot of=/dev/ada0 count=1 
dd if=/boot/zfsboot of=/dev/ada0 iseek=1 oseek=1024
If the drive is currently in use, the GEOM safety will prevent writes and must be disabled before running the above commands:
sysctl kern.geom.debugflags=0x10
zfsboot can also be installed in an MBR slice:
gpart create -s mbr ada0 
gpart add -t freebsd ada0 
gpart bootcode -b /boot/boot0 ada0 
gpart set -a active -i 1 ada0 
dd if=/dev/zero of=/dev/ada0s1 count=2 
dd if=/boot/zfsboot of=/dev/ada0s1 count=1 
dd if=/boot/zfsboot of=/dev/ada0s1 iseek=1 oseek=1024
Note that commands to create and populate a pool are not shown in the example above.

dd(1), boot.config(5), boot(8), gptzfsboot(8), loader(8), zpool(8)

zfsboot appeared in FreeBSD 7.3.

This manual page was written by Andriy Gapon ⟨avg@FreeBSD.org⟩.

Installing zfsboot with dd(1) is a hack. ZFS needs a command to properly install zfsboot onto a ZFS-controlled disk or partition.
March 27, 2018 FreeBSD 12.0-RELEASE

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