freebsd-dev/sys/boot/i386/gptzfsboot/gptzfsboot.8

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.Dd September 15, 2014
.Dt GPTZFSBOOT 8
.Os
.Sh NAME
.Nm gptzfsboot
.Nd GPT bootcode for ZFS on BIOS-based computers
.Sh DESCRIPTION
.Nm
is used on BIOS-based computers to boot from a filesystem in
a ZFS pool.
.Nm
is installed in a
.Cm freebsd-boot
partition of a GPT-partitioned disk with
.Xr gpart 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 BOOTING
.Nm
tries to find all ZFS pools that are composed of BIOS-visible
hard disks or partitions on them.
.Nm
looks for ZFS device labels on all visible disks and in discovered
supported partitions for all supported partition scheme types.
The search starts with the disk from which
.Nm
itself was loaded.
Other disks are probed in BIOS defined order.
After a disk is probed and
.Nm
determines that the whole disk is not a ZFS pool member, then
individual partitions are probed in their partition table order.
Currently GPT and MBR partition schemes are supported.
With the GPT scheme, only partitions of type
.Cm freebsd-zfs
are probed.
The first pool seen during probing is used as a default boot pool.
.Pp
The filesystem specified by the
.Cm bootfs
property of the pool is used as a default boot filesystem.
If the
.Cm bootfs
property is not set, then the root filesystem of the pool is used as
the default.
.Xr zfsloader 8
is loaded from the boot filesystem.
If
.Pa /boot.config
or
.Pa /boot/config
is present in the boot filesystem, boot options are read from it
in the same way as
.Xr boot 8 .
.Pp
The ZFS GUIDs of the first successfully probed device and the first
detected pool are made available to
.Xr zfsloader 8
in the
.Cm vfs.zfs.boot.primary_vdev
and
.Cm vfs.zfs.boot.primary_pool
variables.
.Sh USAGE
Normally
.Nm
will boot in fully automatic mode.
However, like
.Xr boot 8 ,
it is possible to interrupt the automatic boot process and interact with
.Nm
through a prompt.
.Nm
accepts all the options that
.Xr boot 8
supports.
.Pp
Filesystem specification and the path to
.Xr zfsloader 8
is different from
.Xr boot 8 .
The format is
.Pp
.Sm off
.Oo zfs:pool/filesystem: Oc Oo /path/to/loader Oc
.Sm on
.Pp
Both the filesystem and the path can be specified.
If only a path is specified, then the default filesystem is used.
If only a pool and filesystem are specified, then
.Pa /boot/zfsloader
is used as a path.
.Pp
Additionally, the
.Ic status
command can be used to query information about discovered pools.
The output format is similar to that of
.Cm zpool status
.Pq see Xr zpool 8 .
.Pp
The configured or automatically determined ZFS boot filesystem is
stored in the
.Xr zfsloader 8
.Cm loaddev
variable, and also set as the initial value of the
.Cm currdev
variable.
.Sh FILES
.Bl -tag -width /boot/gptzfsboot -compact
.It Pa /boot/gptzfsboot
boot code binary
.It Pa /boot.config
parameters for the boot block
.Pq optional
.It Pa /boot/config
alternative parameters for the boot block
.Pq optional
.El
.Sh EXAMPLES
.Nm
is typically installed in combination with a
.Dq protective MBR
.Po
see
.Xr gpart 8
.Pc .
To install
.Nm
on the
.Pa ada0
drive:
.Bd -literal -offset indent
gpart bootcode -b /boot/pmbr -p /boot/gptzfsboot -i 1 ada0
.Ed
.Pp
.Nm
can also be installed without the PMBR:
.Bd -literal -offset indent
gpart bootcode -p /boot/gptzfsboot -i 1 ada0
.Ed
.Sh SEE ALSO
.Xr boot.config 5 ,
.Xr boot 8 ,
.Xr gpart 8 ,
.Xr loader 8 ,
.Xr zfsloader 8 ,
.Xr zpool 8
.Sh HISTORY
.Nm
appeared in FreeBSD 7.3.
.Sh BUGS
.Nm
looks for ZFS meta-data only in MBR partitions
.Pq known on FreeBSD as slices .
It does not look into BSD
.Xr disklabel 8
partitions that are traditionally called partitions.
If a disklabel partition happens to be placed so that ZFS meta-data can be
found at the fixed offsets relative to a slice, then
.Nm
will recognize the partition as a part of a ZFS pool,
but this is not guaranteed to happen.
.Sh AUTHORS
This manual page was written by
.An Andriy Gapon Aq avg@FreeBSD.org .