sbin/gpt/gpt.8

.\" $NetBSD: gpt.8,v 1.85 2025/01/12 20:48:20 christos Exp $
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.\" Copyright (c) 2002 Marcel Moolenaar
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.\" $FreeBSD: src/sbin/gpt/gpt.8,v 1.17 2006/06/22 22:22:32 marcel Exp $
.\"
.Dd January 12, 2025
.Dt GPT 8
.Os
.Sh NAME
.Nm gpt
.Nd GUID partition table maintenance utility
.Sh SYNOPSIS
.Nm
.Op Fl Hnqrv
.Op Fl m Ar mediasize
.Op Fl s Ar sectorsize
.Op Fl T Ar timestamp
.Ar command
.Op Ar command_options
.Ar device
.Nm
.Ar set
.Fl l
.Nm
.Ar unset
.Fl l
.Nm
.Ar type
.Fl l
.Sh DESCRIPTION
The
.Nm
utility provides the necessary functionality to manipulate GUID partition
tables
.Pq GPTs ,
but see
.Sx BUGS
below for how and where functionality is missing.
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.
.Bl -tag -width XXXX
.It Fl H
Ignore existing MBR (Hybrid MBR/GPT mode).
.It Fl m Ar mediasize
Override the default media size for the device (obtained
from the kernel if possible) or defaulting to the file size for
plain files.
.It Fl n
Do not update the wedge information that
.Nm
changed.
You need to use the
.Xr dkctl 8
command to manually update the device's wedge configuration if you do that.
.It Fl q
Do not print error messages.
This is not implemented completely yet.
.It Fl r
Open the device for reading only.
.Nm
Currently this option is primarily useful for the
.Ic show
command, but the intent is to use it to implement dry-run behaviour.
.It Fl s Ar sectorsize
Override the default sector size for the device (obtained
from the kernel if possible) or
.Dv 512
for plain files.
.It Fl T Ar timestamp
Specify a timestamp to be used for uuid generation so that uuids
are not random and can be consistent for reproducible builds.
The timestamp can be a pathname, where the timestamps are derived from
that file, a parseable date for parsedate(3) (this option is not
yet available in the tools build), or an integer value interpreted
as the number of seconds from the Epoch.
.It Fl v
Controls the verbosity level.
The level increases with every occurrence of this option.
There is no formalized definition of the different levels yet.
.El
.Ss Commands
.Bl -tag -width indent
.\" ==== add ====
.It Nm Ic add Oo Fl a Ar alignment Oc Oo Fl b Ar blocknr Oc \
Oo Fl i Ar index Oc Oo Fl l Ar label Oc Oo Fl s Ar size Oc \
Oo Fl t Ar type Oc
The
.Ic add
command allows the user to add a new partition to an existing table.
By default, it will create a UFS 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 a Ar alignment
option allows the user to specify an alignment for the start and size.
The alignment is given in bytes and may have a suffix to indicate its
magnitude.
.Nm
will attempt to align the partition.
.Pp
The
.Fl b Ar blocknr
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.
.Pp
The
.Fl l Ar label
option allows the user to specify a label for the partition.
.Pp
The
.Fl s Ar size
option allows the user to specify the size of the partition.
If there is no suffix, or the suffix is
.Sq s
or
.Sq S
then size is in sectors, otherwise size is in bytes which must be
a multiple of the device's sector size.
Accepted suffix units (case insensitive) are
.Sq b
to denote bytes,
.Sq k
to denote kilobytes,
.Sq m
to denote megabytes and
.Sq g
to denote gigabytes,
.Sq t
to denote terabytes,
.Sq p
to denote petabytes, and
.Sq e
to denote exabytes.
The minimum size is 1 sector.
.Pp
The
.Fl t Ar type
option allows the user to specify the partition type.
The type is given as a UUID, but
.Nm
accepts
.Bl -tag -width "windows-reserved" -compact -offset indent
.It Cm apple
Apple HFS
.It Cm apple-ufs
Apple UFS
.It Cm bios
BIOS Boot
.It Cm efi
EFI System
.It Cm fbsd-legacy
.Fx
legacy
.It Cm fbsd-swap
.Fx
swap
.It Cm fbsd-ufs
.Fx
UFS/UFS2
.It Cm fbsd-vinum
.Fx
vinum
.It Cm zfs
.Fx ,
.Nx
ZFS
.It Cm linux-data
Linux data
.It Cm linux-raid
Linux RAID
.It Cm linux-swap
Linux swap
.It Cm linux-lvm
Linux LVM
.It Cm obsd
OpenBSD data
.It Cm windows
Microsoft basic data - NTFS, FAT32 ("msdos"), FAT16, also used for UDF
.It Cm windows-reserved
Microsoft reserved
.It Cm ccd
.Nx
ccd component
.It Cm cgd
.Nx
Cryptographic Disk
.It Cm ffs
.Nx
FFSv1/FFSv2
.It Cm lfs
.Nx
LFS
.It Cm raid
.Nx
RAIDFrame component
.It Cm swap
.Nx
swap
.El
as aliases for the most commonly used partition types.
.\" ==== backup ====
.It Nm Ic backup Oo Fl o Ar outfile Oc
The
.Ic backup
command dumps the MBR or (PMBR) and GPT partition tables to standard
output or to a file specified by the
.Ar outfile
argument in a format to be used by the
.Ic restore
command.
The format is a plist.
It should not be modified.
.\" ==== biosboot ====
.It Nm Ic biosboot Oo Fl A Oc Oo Fl c Ar bootcode Oc Oo Fl b Ar startsec Oc \
Oo Fl i Ar index Oc Oo Fl L Ar label Oc
The
.Ic biosboot
command allows the user to configure the partition that contains the
primary bootstrap program, used during
.Xr boot 8 .
.Pp
The
.Fl A
options sets the PMBR partition active.
This should not normally be necessary,
but some firmware might require it.
If
.Fl A
is omitted, the active flag will be cleared from the PMBR label.
.Pp
The
.Fl c
option allows the user to specify the filename from which
.Nm
should read the bootcode.
The default is to read from
.Pa /usr/mdec/gptmbr.bin .
.Pp
The partition that should contain the primary bootstrap code,
.Pq similar to that installed via Xr installboot 8
is selected using the
.Fl i ,
.Fl L
and
.Fl b
options.
One of these three options is required.
The
.Fl i
option selects the partition given by the
.Ar index .
The
.Fl L
option selects the partition by
.Ar label .
If there are multiple partitions with the same label,
the first one found will be used.
The
.Fl b
option selects the partition starting at block
.Ar startsec .
.\" ==== create ====
.It Nm Ic create Oo Fl AfP Oc Oo Fl p Ar partitions Oc
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 A
options sets the PMBR partition active.
.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.
.Pp
The
.Fl p
option changes the default 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).
.\" ==== destroy ====
.It Nm Ic destroy Oo Fl r Oc
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.
.\" ==== header ====
.It Nm Ic header
The
.Ic header
command displays size information about the media and information from the
GPT header if it exists.
.\" ==== label ====
.It Nm Ic label Oo Fl a Oc Ao Fl f Ar file | Fl l Ar label Ac
.It Nm Ic label Oo Fl b Ar blocknr Oc Oo Fl i Ar index Oc \
Oo Fl L Ar label Oc Oo Fl s Ar sectors Oc Oo Fl t Ar type Oc \
Ao Fl f Ar file | Fl l Ar label Ac
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 blocknr
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.
.Pp
The
.Fl L Ar label
option selects all partitions that have the given label.
This can cause multiple partitions to be relabeled.
.Pp
The
.Fl s Ar sectors
option selects all partitions that have the given size.
This can cause multiple partitions to be labeled.
.Pp
The
.Fl t Ar type
option selects all partitions that have the given type.
The type is given as a UUID or by the aliases that the
.Ic add
command accepts.
This can cause multiple partitions to be labeled.
.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 Afs Oc Oo Fl p Ar partitions Oc
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 A
options sets the PMBR partition active.
.Pp
The
.Fl s
option prevents migrating
.Bx
disk labels into GPT partitions by creating
the GPT equivalent of a slice.
Note that the
.Fl s
option is not applicable to
.Nx
partitions.
.Pp
The
.Fl p
option changes the default 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
.Ic migrate
command requires space at the beginning and the end of the device outside
any partitions to store the GPTs.
Space is required for the GPT header
.Pq which takes one sector
and the GPT partition table.
See the
.Fl p
option
for the size of the GPT partition table.
By default, just about all devices have a minimum of 62 sectors free at the
beginning of the device, but do not have any free space at the end.
For the default GPT partition table size on a 512 byte sector size device,
33 sectors at the end of the device would need to be freed.
.\" ==== recover ====
.It Nm Ic recover
The
.Ic recover
command tries to restore the GPT partition label from the backup
near the end of the disk.
It is very useful in case the primary label was deleted.
.\" ==== remove ====
.It Nm Ic remove Oo Fl a Oc
.It Nm Ic remove Oo Fl b Ar blocknr Oc Oo Fl i Ar index Oc \
Oo Fl L Ar label Oc Oo Fl s Ar sectors Oc Oo Fl t Ar type Oc
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.
.\" ==== resize ====
.It Nm Ic resize Oo Fl i Ar index Oc Oo Fl b Ar startsec Oc Oo Fl a Ar alignment Oc \
Oo Fl s Ar size Oc Oo Fl q Oc
The
.Ic resize
command allows the user to resize a partition.
The partition may be shrunk and if there is sufficient free space
immediately after it then it may be expanded.
The
.Fl s
option allows the new size to be specified, otherwise the partition will
be increased to the maximum available size.
If there is no suffix, or the suffix is
.Sq s
or
.Sq S
then size is in sectors, otherwise size is in bytes which must be
a multiple of the device's sector size.
Accepted suffix units are
.Sq b
to denote bytes,
.Sq k
to denote kilobytes,
.Sq m
to denote megabytes and
.Sq g
to denote gigabytes.
The minimum size is 1 sector.
If the
.Fl a
option is specified then the size will be adjusted to be a multiple of
alignment if possible.
If the
.Fl q
option is specified then the utility will not print output when a
resize is not required.
.\" ==== resizedisk ====
.It Nm Ic resizedisk Oo Fl s Ar size Oc Oo Fl q Oc
The
.Ic resizedisk
command allows the user to resize a disk.
With GPTs, a backup copy is stored at the end of the disk.
If the underlying medium changes size
.Pq or is going to change size ,
then the backup copy needs to be moved to the new end of the disk,
and the last sector available for data storage needs to be adjusted.
This command does that.
If the backup copy no longer exists due to the medium shrinking, then
a new backup copy will be created using the primary copy.
.Pp
The
.Fl s
option allows the new size to be specified, otherwise the backup copy
will automatically be placed at the current end of the disk.
If there is no suffix, or the suffix is
.Sq s
or
.Sq S
then size is in sectors, otherwise size is in bytes which must be
a multiple of the device's sector size.
Accepted suffix units are
.Sq b
to denote bytes,
.Sq k
to denote kilobytes,
.Sq m
to denote megabytes and
.Sq g
to denote gigabytes.
Using the
.Fl s
option allows you to move the backup copy prior to resizing the medium.
This is primarily useful when shrinking the medium.
If the
.Fl q
option is specified then the utility will not print output when a
resize is not required.
.\" ==== restore ====
.It Nm Ic restore Oo Fl F Oc Oo Fl i Ar infile Oc
The
.Ic restore
command restores a partition table that was previously saved using the
.Ic backup
command.
The partition table is read from standard input or a file specified in
the
.Ar infile
argument and is expected to be in the format of a plist.
It assumes an empty disk.
The
.Fl F
option can be used to blank the disk.
The new disk does not have to be the same size as the old disk as long as all
the partitions fit, as
.Ic restore
will automatically adjust.
However, the new disk must use the same sector size as the old disk.
.\" ==== set ====
.It Nm Ic set Oo Fl a Ar attribute Oc Oo Fl N Oc Oo Fl i Ar index Oc \
Oo Fl b Ar startsec Oc
.It Nm Ic set Fl l
The
.Ic set
command sets various partition attributes.
The
.Fl l
flag lists all available attributes.
The
.Fl a
option specifies which attributes to set and may be specified more than once,
or the attributes can be comma-separated.
If the
.Fl N
option and no
.Fl a
option are specified, all attributes are removed.
The
.Fl i
or the
.Fl b
option specify which entry to update.
The possible attributes are
.Do biosboot Dc ,
.Do bootme Dc ,
.Do bootonce Dc ,
.Do bootfailed Dc ,
.Do noblockio Dc , and
.Do required Dc .
The biosboot flag is used to indicate which partition should be booted
by legacy BIOS boot code.
See the
.Ic biosboot
command for more information.
The bootme flag is used to indicate which partition should be booted
by UEFI boot code.
The other attributes are for compatibility with
.Fx
and are not currently used by
.Nx .
They may be used by
.Nx
in the future.
.\" ==== show ====
.It Nm Ic show Oo Fl aglux Oc Oo Fl i Ar index Oc Oo Fl b Ar startsec Oc
The
.Ic show
command displays the current partitioning on the listed devices and gives
an overall view of the disk contents.
With the
.Fl g
option the GPT partition GUID will be displayed instead of the GPT partition
type.
With the
.Fl l
option the GPT partition label will be displayed instead of the GPT partition
type.
With the
.Fl u
option the GPT partition type is displayed as a UUID instead of in a
user friendly form.
With the
.Fl i
or the
.Fl b
option, all the details of a particular GPT partition will be displayed.
The format of this display is subject to change.
With the
.Fl a
option, all information for all GPT partitions (just like with
.Fl i Ar index )
will be printed.
The
.Fl x
option prints start/size in hex.
None of the options have any effect on non-GPT partitions.
The order of precedence for the options is:
.Fl a ,
.Fl i ,
.Fl l ,
.Fl g ,
.Fl u ,
.Fl x .
.\" ==== type ====
.It Nm Ic type Oo Fl a Oc Fl T Ar newtype
.It Nm Ic type Oo Fl b Ar blocknr Oc Oo Fl i Ar index Oc \
Oo Fl L Ar label Oc Oo Fl s Ar sectors Oc Oo Fl t Ar type Oc \
Fl T Ar newtype
.It Nm Ic type Fl l
The
.Ic type
command allows the user to change the type of 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.
The
.Fl l
flag lists available types.
.\" ==== unset ====
.It Nm Ic unset Fl a Ar attribute Oo Fl i Ar index Oc Oo Fl b Ar startsec Oc
.It Nm Ic unset Fl l
The
.Ic unset
command unsets various partition attributes.
The
.Fl l
flag lists all available attributes.
The
.Fl a
option specifies which attributes to unset and may be specified more than once.
Alternatively a comma separated list of attributes can be used.
The
.Fl i
or the
.Fl b
option specifies which entry to update.
The possible attributes are
.Do biosboot Dc ,
.Do bootme Dc ,
.Do bootonce Dc ,
.Do bootfailed Dc ,
.Do noblockio Dc , and
.Do required Dc .
The biosboot flag is used to indicate which partition should be booted
by legacy BIOS boot code.
See the
.Ic biosboot
command for more information.
The other attributes are for compatibility with
.Fx
and are not currently used by any
.Nx
code.
They may be used by
.Nx
code in the future.
.\" ==== uuid ====
.It Nm Ic uuid Oo Fl a Oc
.It Nm Ic uuid Oo Fl b Ar blocknr Oc Oo Fl i Ar index Ar Oc \
Oo Fl L Ar label Oc Oo Fl s Ar sectors Oc Oo Fl t Ar type Oc \
Oo Fl U Ar newuuid Oc
The
.Ic uuid
command allows the user to change the UUID of 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.
If
.Ar newuuid
is not specified, a random UUID value is derived from the timestamp
.Po see the
.Fl T
option
.Pc .
If
.Fl a
is used, then the header UUID is changed as well.
.Pp
The primary purpose of this command is for use after cloning a disk to
prevent collisions when both disks are used in the same system.
.\" ==== end of commands ====
.El
.Sh EXIT STATUS
The
.Nm
command exits with a failure status (1) when the header command
is used and no GPT header is found.
This can be used to check for the existence of a GPT in shell scripts.
.Sh EXAMPLES
.Bd -literal
nas# gpt show wd3
       start        size  index  contents
           0           1         PMBR
           1  3907029167
nas# gpt create wd3
nas# gpt show wd3
       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34  3907029101
  3907029135          32         Sec GPT table
  3907029167           1         Sec GPT header
nas# gpt add -s 10486224 -t swap -i 1 wd3
nas# gpt label -i 1 -l swap_1 wd3
partition 1 on rwd3d labeled swap_1
nas# gpt show wd3
       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34    10486224      1  GPT part - NetBSD swap
    10486258  3896542877
  3907029135          32         Sec GPT table
  3907029167           1         Sec GPT header
nas# gpt show -l wd3
       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34    10486224      1  GPT part - "swap_1"
    10486258  3896542877
  3907029135          32         Sec GPT table
  3907029167           1         Sec GPT header
nas#
.Ed
.Pp
Booting from GPT on a BIOS system: this creates a bootable partition.
.Bd -literal
xotica# gpt create wd1
xotica# gpt add -b 1024 -l bootroot -t ffs -s 1g wd1
/dev/rwd1: Partition 1 added: 49f48d5a-b10e-11dc-b99b-0019d1879648 1024 2097152
xotica ~# dmesg | tail -2
wd1: GPT GUID: 660e0630-0a3f-47c0-bc52-c88bcec79392
dk0 at wd1: "bootroot", 2097152 blocks at 1024, type: ffs
xotica# gpt biosboot -L bootroot wd1
xotica# newfs dk0
xotica# installboot /dev/rdk0 /usr/mdec/bootxx_ffsv1
xotica# mount /dev/dk0 /mnt
xotica# cp /usr/mdec/boot /mnt
.Ed
.Pp
Note that
.Ic biosboot
is not needed for UEFI systems.
.Sh SEE ALSO
.Xr boot 8 ,
.Xr dkctl 8 ,
.Xr fdisk 8 ,
.Xr installboot 8 ,
.Xr mount 8 ,
.Xr newfs 8 ,
.Xr swapctl 8
.Sh HISTORY
The
.Nm
utility appeared in
.Fx 5.0
for ia64.
.Nm
utility first appeared in
.Nx 5.0 .
.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 will not change, but it is
possible that future versions will not be compatible in the strictest sense
of the word.
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.