gpt.8: Update example and note

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.\" $FreeBSD: src/sbin/gpt/gpt.8,v 1.17 2006/06/22 22:22:32 marcel Exp $
.\" $DragonFly: src/sbin/gpt/gpt.8,v 1.14 2008/10/03 21:26:28 thomas Exp $
.\"
.Dd September 28, 2009
.Os
.Dt GPT 8
.Sh NAME
.Nm gpt
.Nd "GUID partition table maintenance utility"
.Sh SYNOPSIS
.Nm
.Op Ar general_options
.Ar command
.Op Ar command_options
.Ar device ...
.Sh DESCRIPTION
The
.Nm
utility provides the necessary functionality to manipulate GUID partition
tables (GPTs), but see
.Sx BUGS
below for how and where functionality is missing.
GPT partitions are accessed as
.Dx
disk slices, with same number as GPT partition,
127 slices per disk device are supported.
The basic usage model of the
.Nm
tool follows that of the
.Xr cvs 1
tool.
The general options are described in the following paragraph.
The remaining paragraphs describe the individual commands with their options.
Here we conclude by mentioning that a
.Ar device
is either a special file
corresponding to a disk-like device or a regular file.
The command is applied to each
.Ar device
listed on the command line.
.Ss General Options
The general options allow the user to change default settings or otherwise
change the behaviour that is applicable to all commands.
Not all commands use all default settings, so some general options may not
have an effect on all commands.
.Pp
The
.Fl p Ar count
option allows the user to change the number of partitions the GPT can
accommodate.
This is used whenever a new GPT is created.
By default, the
.Nm
utility will create space for 128 partitions (or 32 sectors of 512 bytes).
.Pp
The
.Fl r
option causes the
.Nm
utility to open the device for reading only.
Currently this option is primarily useful for the
.Ic show
command, but the intent
is to use it to implement dry-run behaviour.
.Pp
The
.Fl v
option controls the verbosity level.
The level increases with every occurrence of this option.
There is no formalized definition of the different levels yet.
.Ss Commands
.Bl -tag -width indent
.\" ==== add ====
.It Xo
.Nm
.Ic add
.Op Fl b Ar number
.Op Fl i Ar index
.Op Fl s Ar count
.Op Fl t Ar type
.Ar device ...
.Xc
The
.Ic add
command allows the user to add a new partition to an existing table,
the name of the disk slice for the added partition is printed.
By default, it will create a
.Cm dfly
partition covering the first available block
of an unused disk space.
The command-specific options can be used to control this behaviour.
.Pp
The
.Fl b Ar number
option allows the user to specify the starting (beginning) sector number of
the partition.
The minimum sector number is 1, but has to fall inside an unused region of
disk space that is covered by the GPT.
.Pp
The
.Fl i Ar index
option allows the user to specify which (free) entry in the GPT table is to
be used for the new partition.
By default, the first free entry is selected.
Entries start at index 0 representing partition 0 of the GPT.
.Pp
The
.Fl s Ar count
option allows the user to specify the size of the partition in sectors.
The minimum size is 1.
.Pp
The
.Fl t Ar type
option allows the user to specify the partition type.
The type is given as an UUID, but
.Nm
accepts
.Cm efi , swap , ufs , hfs , linux , dfly ,
and
.Cm windows
as aliases for the most commonly used partition types.
.Cm ufs
is a
.Fx
UFS UUID.
.Cm dfly
has the alias
.Cm dragonfly
and is a
.Dx
.Xr disklabel64 5
UUID.
You may also specify any symbolic name in the system
.Xr uuids 5
files.
.\" ==== boot ====
.It Nm Ic boot Ar device ...
The
.Ic boot
command allows the user to create a small boot partition in a freshly
created GPT.
.Pp
This command creates a small, 256MB boot partition as partition #0
and hacks in a special
.Sq slice 1
in the PMBR which aliases it.
The PMBR is further modified to add the necessary boot code.
You can then disklabel GPT partition #0 and mount it, placing the contents of
.Pa /boot
directory within.
You must add a line to
.Pa loader.conf ,
like
.Bd -literal -offset indent
vfs.root.mountfrom="ufs:da1s1a"
.Ed
.Pp
which point to the actual root mount.
.Pp
Your root partition may be another GPT partition and you may use a 64 bit
disklabel within that partition if you desire.
.Pp
The
.Sq boot0
boot manager is used, it can be manipulated with the
.Xr boot0cfg 8
command,
.Sq packet
option usually needs to be set.
.Pp
.Em NOTE!
A disk setup with the
.Ar boot
command may not be shared with another OS,
as it doesn't use a fully standard GPT.
.Pp
.Em WARNING!
Some BIOSes may not be able to deal with this hack, your mileage may vary.
.\" ==== create ====
.It Nm Ic create Oo Fl fp Oc Ar device ...
The
.Ic create
command allows the user to create a new (empty) GPT.
By default, one cannot create a GPT when the device contains a MBR,
however this can be overridden with the
.Fl f
option.
If the
.Fl f
option is specified, an existing MBR is destroyed and any partitions
described by the MBR are lost.
.Pp
The
.Fl p
option tells
.Nm
to create only the primary table and not the backup table.
This option is only useful for debugging and should not be used otherwise.
.\" ==== destroy ====
.It Nm Ic destroy Oo Fl r Oc Ar device ...
The
.Ic destroy
command allows the user to destroy an existing, possibly not empty GPT.
.Pp
The
.Fl r
option instructs
.Nm
to destroy the table in a way that it can be recovered.
.\" ==== label ====
.It Xo
.Nm
.Ic label
.Op Fl a
.Aq Fl f Ar file | Fl l Ar label
.Ar device ...
.Xc
.It Xo
.Nm
.Ic label
.Op Fl b Ar number
.Op Fl i Ar index
.Op Fl s Ar count
.Op Fl t Ar type
.Aq Fl f Ar file | Fl l Ar label
.Ar device ...
.Xc
The
.Ic label
command allows the user to label any partitions that match the selection.
At least one of the following selection options must be specified.
.Pp
The
.Fl a
option specifies that all partitions should be labeled.
It is mutually exclusive with all other selection options.
.Pp
The
.Fl b Ar number
option selects the partition that starts at the given block number.
.Pp
The
.Fl i Ar index
option selects the partition with the given partition number.
Partition numbers start at 0.
.Pp
The
.Fl s Ar count
option selects all partitions that have the given size.
This can cause multiple partitions to be removed.
.Pp
The
.Fl t Ar type
option selects all partitions that have the given type.
The type is given as an UUID or by the aliases that the
.Ic add
command accepts.
This can cause multiple partitions to be removed.
.Pp
The
.Fl f Ar file
or
.Fl l Ar label
options specify the new label to be assigned to the selected partitions.
The
.Fl f Ar file
option is used to read the label from the specified file.
Only the first line is read from the file and the trailing newline
character is stripped.
If the file name is the dash or minus sign
.Pq Fl ,
the label is read from
the standard input.
The
.Fl l Ar label
option is used to specify the label in the command line.
The label is assumed to be encoded in UTF-8.
.\" ==== migrate ====
.It Nm Ic migrate Oo Fl fs Oc Ar device ...
The
.Ic migrate
command allows the user to migrate an MBR-based disk partitioning into a
GPT-based partitioning.
By default, the MBR is not migrated when it contains partitions of an unknown
type.
This can be overridden with the
.Fl f
option.
Specifying the
.Fl f
option will cause unknown partitions to be ignored and any data in it
to be lost.
.Pp
The
.Fl s
option prevents migrating
.Bx
disk labels into GPT partitions by creating
the GPT equivalent of a slice.
.\" ==== remove ====
.It Nm Ic remove Oo Fl a Oc Ar device ...
.It Xo
.Nm
.Ic remove
.Op Fl b Ar number
.Op Fl i Ar index
.Op Fl s Ar count
.Op Fl t Ar type
.Ar device ...
.Xc
The
.Ic remove
command allows the user to remove any and all partitions that match the
selection.
It uses the same selection options as the
.Ic label
command.
See above for a description of these options.
Partitions are removed by clearing the partition type.
No other information is changed.
.\" ==== show ====
.It Nm Ic show Oo Fl lu Oc Ar device ...
The
.Ic show
command displays the current partitioning on the listed devices and gives
an overall view of the disk contents.
With the
.Fl l
option the GPT partition label will be displayed instead of the GPT partition
type.
The option has no effect on non-GPT partitions.
With the
.Fl u
option the GPT partition type is displayed as an UUID instead of in a
user friendly form.
The
.Fl l
option takes precedence over the
.Fl u
option.
.El
.Sh FILES
.Bl -tag -width ".Pa /etc/defaults/uuids"
.It Pa /boot/boot0
The default
.Sq boot0
image.
.It Pa /etc/defaults/uuids
A list of UUIDs
and their symbolic names provided by the OS vendor.
.It Pa /etc/uuids
A list of UUIDs
and their symbolic names provided by the system administrator.
.El
.Sh EXAMPLES
To install an empty GPT on
.Pa ad6 :
.Pp
.Dl "gpt create ad6"
.Pp
GPT partitions are defined in number of sectors, the sector size is usually 512B,
which is assumed in the examples below, it can be found using:
.Pp
.Dl "gpt -v show ad6"
.Pp
To add a dummy GPT partition 0:
.Pp
.Dl "gpt add -i0 -s16 ad6"
.Pp
You might want to do this to not use slice 0 for data;
when GPT is not used on a disk, slice 0 is the compatibility slice,
which is used for
.Dq dangerously dedicated
disks.
For GPT slice 0 has no special meaning, it is just the first slice on the disk.
.Pp
To add a GPT partition of size approx. 100GB:
.Pp
.Dl "gpt add -s200000000 ad6"
.Pp
This will be GPT partition 1 as it is the first one free,
it will be accessible as
.Pa ad6s1 ,
which is also printed by the command.
The type will be
.Dq DragonFly Label64 ,
it will have to be set up by
.Xr disklabel64 8 .
.Pp
To add GPT partition 5 with type
.Dq DragonFly HAMMER
using the remaining free space:
.Bd -literal -offset indent
gpt add -i5 -t "DragonFly HAMMER" ad6
.Ed
.Pp
To print the contents of the GPT:
.Pp
.Dl "gpt show ad6"
.Ss Boot Setup
To setup a disk using GPT for booting, the steps below can be used.
System is copied from an already installed disk,
e.g.\& a hard disk or an install CD.
This example will setup disk
.Pa da1
with GPT for booting, using the
.Ic boot
command.
.Pp
.Em WARNING!
Any previous data on disk installed to will be deleted.
.Bd -literal -offset indent
gpt create -f da1
gpt boot da1
boot0cfg -s 2 da1
disklabel -B -r -w da1s0 auto
disklabel -e da1s0	# add `a: * * 4.2BSD', to add `a' partition
			#   with fstype `4.2BSD' covering whole slice

gpt add da1
disklabel64 -r -w da1s1 auto
disklabel64 -e da1s1	# add `b: 4G * swap', to add `b' partition
			#   with fstype `swap' and size 4GB,
			# add `a: * * HAMMER', to add `a' partition
			#   with fstype `HAMMER' covering rest of slice
newfs_hammer -L ROOT /dev/da1s1a
mount_hammer /dev/da1s1a /mnt

newfs /dev/da1s0a
mkdir /mnt/boot
mount /dev/da1s0a /mnt/boot

cpdup / /mnt		# copy each file system you need, e.g.
cpdup /boot /mnt/boot
cpdup /var /mnt/var
cpdup /var/tmp /mnt/var/tmp
cpdup /usr /mnt/usr

cd /mnt
vi etc/fstab		# add `/dev/da1s1a / hammer rw',
			# add `/dev/da1s1b none swap sw',
			# add `/dev/da1s0a /boot ufs rw 1 1',
			# delete lines for file systems cpdup'ed above
vi boot/loader.conf	# add `vfs.root.mountfrom="hammer:da1s1a"'
cd
umount /mnt/boot
umount /mnt
.Ed
.Sh COMPATIBILITY
The GPT that
.Nm
manipulates is part of the EFI standard and is supported by many OSs.
GPT uses 64 bits to store number of sectors, this supports very large disks.
With the prevalent sector size of 512B this is 8 billion TB.
.Sh SEE ALSO
.Xr uuid 3 ,
.Xr disklabel64 5 ,
.Xr uuids 5 ,
.Xr boot0cfg 8 ,
.Xr disklabel 8 ,
.Xr disklabel64 8 ,
.Xr fdisk 8 ,
.Xr mount 8 ,
.Xr newfs 8 ,
.Xr newfs_hammer 8 ,
.Xr swapon 8
.Sh HISTORY
The
.Nm
utility appeared in
.Fx 5.0
for ia64.
It was imported to
.Dx 1.9 .
.Sh BUGS
The development of the
.Nm
utility is still work in progress.
Many necessary features are missing or partially implemented.
In practice this means that the manual page, supposed to describe these
features, is farther removed from being complete or useful.
As such, missing functionality is not even documented as missing.
However, it is believed that the currently present functionality is reliable
and stable enough that this tool can be used without bullet-proof footware if
one thinks one does not make mistakes.
.Pp
It is expected that the basic usage model does not change, but it is
possible that future versions will not be compatible in the strictest sense
of the word.
For example, the
.Fl p Ar count
option may be changed to a command option rather than a generic option.
There are only two commands that use it so there is a chance that the natural
tendency for people is to use it as a command option.
Also, options primarily intended for diagnostic or debug purposes may be
removed in future versions.
.Pp
Another possibility is that the current usage model is accompanied by
other interfaces to make the tool usable as a back-end.
This all depends on demand and thus feedback.
.Pp
The
.Ic migrate
command doesn't support
.Dx
partition types.