.\" $NetBSD: gpt.8,v 1.89 2026/02/17 01:41:56 kre Exp $
.\"
.\" Copyright (c) 2002 Marcel Moolenaar
.\" All rights reserved.
.\"
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.\" modification, are permitted provided that the following conditions
.\" are met:
.\"
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\" $FreeBSD: src/sbin/gpt/gpt.8,v 1.17 2006/06/22 22:22:32 marcel Exp $
.\"
.Dd February 9, 2026
.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
.Op Fl qv
.Cm set
.Fl l
.Nm
.Op Fl qv
.Cm unset
.Fl l
.Nm
.Op Fl qv
.Cm type
.Fl l
.sp 0.3v
.Nm nbgpt
.Op Fl Hnqrv
.Op Fl m Ar mediasize
.Op Fl s Ar sectorsize
.Op Fl T Ar timestamp
.Ar device
.Ar command
.Op Ar command_options
.Sh DESCRIPTION
The
.Nm gpt
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.
A
.Ar device
is either a special file
corresponding to a disk-like device or a regular file.
.\"
.\"XXX Who dreamed up this insanity?   It is wrong, and
.\"XXX wouldn't be useful, or desirable, in any case.
.\"XXX It is also close to unimplementable (particularly with
.\"XXX the current ambidextrous device specification positioning.
.\" The command is applied to each
.\" .Ar device
.\" listed on the command line.
The
.Ar command
specifies the operation to be performed upon the GPT of the
.Ar device
specified.
Commands possible are listed below.
.Pp
Note that when built as a tool, and named
.Dq Cm nbgpt
or when run using any other filesystem name than
.Dq Nm
the (usually required)
.Ar device
parameter is placed between the general options and the
.Ar command
name specified, rather than at the end of the argument list.
.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.
These options are given before the
.Ar command
name.
Each (or at least most) of the
.Ar command Ns s
has options of its own, specified below, which follow the
.Ar command
name.
The same option letter may be used, with different effects,
as a general and command specific option.
.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.
This size is in units of bytes, but can be scaled by adding
one of the suffixes allowed for the
.Ar size
in the
.Cm add
command below
.Po
except for
.Sq e
which is not implemented here
.Pc .
If this option is given,
and
.Fl r
is neither given nor implied,
then
.Ar device
is permitted to be an empty,
or even not yet existing,
ordinary file.
.It Fl n
Do not update the kernel's wedge information to reflect
changes made by
.Nm .
The
.Xr dkctl 8
command can be used later
to manually update the kernel's wedge configuration for the
.Ar device
if
.Fl n
is used.
.It Fl q
Do not print error messages.
This is not implemented completely yet.
.It Fl r
Open the device for reading only.
Currently this option is primarily useful for the
.Ic show
and
.Ic header
commands (where it is the default),
but the intent is to also use it to implement dry-run behaviour.
This is implied if the device can be opened for reading,
but not for writing,
and is always applied when the
.Ar command
given does not ever require write access.
.It Fl s Ar sectorsize
Override the default sector size for the
.Ar device
.Po
obtained from the kernel if possible, or
.Dv 512
for plain files
.Pc .
The sector size is given as a simple (unsigned) integer,
possibly scaled by a
.Sq K
suffix, indicating kilobytes (KiB),
specifying the number of bytes in each sector.
This option usually needs to be repeated with every
command applied to the affected
.Ar device .
.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.
Each time a command which will create uuids is run,
e.g.:
.Nm
.Cm add ,
.Nm
.Cm create ,
.Nm
.Cm migrate ,
or
.Nm
.Cm uuid ,
with the same
.Ar device
or another device which will be used in the same system,
if
.Fl T
is to be used,
it should be given a different timestamp from that used with
any other uuid which might be used in the same system as
.Ar device .
Otherise the same uuids will be generated for multiple uses,
and not be unique.
This option should not be used other than for testing,
or making temporary filesystems for distributions, etc.
When this option is not given,
timestamps are based upon a random number supplied by the kernel.
.Pp
The
.Ar timestamp
can be a pathname,
where the timestamps are derived from the file named,
an integer value interpreted
as the number of seconds from the Epoch,
or a parsable date string for parsedate(3) (this final option is not
yet available in the tools build).
.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
.Pp
.Bl -tag -width indent -compact
.\" ==== add ====
.Pp
.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
.Pp
The
.Ic add
command allows the user to add a new partition to an existing table.
By default,
it will create an unlabeled UFS partition
starting at 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, see the
.Fl s
option description just below.
.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.
When not given
.Nm
will select a suitable available empty space, if any exists.
.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.
See the description of the
.Nm
.Cm label
command for more information on labels.
.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,
.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.
If not specified,
.Nm
will use all of the available space in the
empty area selected by the
.Fl b
option, after the selected
.Ar blocknr ,
subject to alignment constraints.
.Pp
The
.Fl t Ar type
option allows the user to specify the partition type.
If this option is omitted,
a
.Nx
FFS partition type
.Pq Cm ffs
will be created.
The type can be given as a UUID, but
.Nm
accepts, amongst others:
.Bl -tag -width "windows-reserved" -compact -offset indent
.It Cm efi
EFI System
.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
.It Cm zfs
.Nx
or
.Fx
ZFS
.It Cm fbsd-ufs
.Fx
UFS/UFS2
.It Cm fbsd-swap
.Fx
swap
.It Cm apple
Apple HFS
.It Cm bios
BIOS Boot
.It Cm linux-data
Linux data
.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
.El
as aliases for the most commonly used partition types.
.br
Use:
.Do
.Nm
.Cm type Fl l
.Dc
to obtain an up to date list of the supported aliases.
.\" ==== backup ====
.Pp
.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 ====
.Pp
.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
when the system firmware (BIOS) either cannot handle EFI
booting, or is configured not to.
.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 header.
.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 ====
.Pp
.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 an 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.
See the
.Cm migrate
command below for an alternative.
A PMBR header,
with one allocated partition
.Pq the GPT partition ,
covering the entire
.Ar device ,
is created.
.Pp
The
.Fl A
option 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 set whenever a new GPT is created,
and can only
.Pq currently
be changed by destroying the GPT and beginning again.
By default, the
.Nm
utility will create space for 128 partitions
.Pq 32 sectors if they are each 512 bytes .
The
.Ar partitions
value given will be rounded up as needed so that no free space remains
in the last allocated partition table sector.
The number of partition table entries per sector varies with the
sector size.
.Pq It is assumed that sector sizes are a power of two, and not less than 128.
.\" ==== destroy ====
.Pp
.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 ====
.Pp
.It Nm Ic header
The
.Ic header
command displays size information about the media
.Pq Ar device
and information from its
GPT header if it exists.
.\" ==== label ====
.Pp
.It Nm Ic label Fl a Ao Fl f Ar file | Fl l Ar newlabel 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 newlabel Ac
.Pp
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
When more than one of the
.Fl b ,
.Fl i ,
.Fl L ,
.Fl s
and
.Fl t
options are given, partitions much match all the given
criteria to be selected.
For this reason it is rarely useful to specify either
.Fl b
or
.Fl i
.Pq which can each only ever select one partition
with each other, or any of the other selection options,
unless the intent is something like:
.Dq Partition N provided that its X is Y
.Pq and otherwise nothing .
.Pp
A label consists of up to 36 characters (not bytes), and can contain
anything from the Unicode character set, with a 16 bit code-point,
except the NUL
.Pq Sq \e0
character.
Uses of the label for other purposes generally restrict the useful
character set to exclude white space and newlines,
and often other unprintable characters,
and may impose a much shorter length restriction,
which would usually apply to the size of the label when encoded
in its input/output UTF-8 format.
.Pp
The
.Fl f Ar file
or
.Fl l Ar newlabel
options specify the new label to be assigned to the selected partitions.
The
.Fl f Ar file
option is used to read the new 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 new label is read from
the standard input.
The
.Fl l Ar newlabel
option is used to specify the new label on the command line.
With either option,
the new label supplied is assumed to be encoded in UTF-8.
Setting the label to be an empty string effectively causes
the label to be removed.
.\" ==== migrate ====
.Pp
.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 them
to be lost.
.Pp
The
.Fl A
option 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,
as with the similar option to the
.Nm
.Cm create
command.
This is set whenever a new GPT is created.
By default,
the
.Nm
utility will create space for 128 partitions.
.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 many 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 ====
.Pp
.It Nm Ic recover
The
.Ic recover
command tries to restore the GPT partition label from the backup
near the end of the
.Ar device .
It is useful in case the primary label was deleted or overwritten,
and rarely otherwise.
.\" ==== remove ====
.Pp
.It Nm Ic remove Fl a
.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 ====
.Pp
.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 and must be
a multiple of the device's sector size.
Accepted suffix units are the same as those allowed for the
.Ar size
parameter to the
.Nm
.Cm add
command.
The minimum size is 1 sector.
If the
.Fl a
option is specified then the size will be adjusted to be a multiple of
.Ar alignment
if possible.
If the
.Fl q
option is specified then the utility will not print output when a
resize is not required.
.\" ==== resizedisk ====
.Pp
.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 of the label is stored at the end of the disk.
If the underlying medium changes size
.Pq or is going to change size ,
then the backup label 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 as for the
.Ar size
parameter of the
.Nm
.Cm add
command.
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 ====
.Pp
.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 ====
.Pp
.It Nm Ic set Fl l
.It Nm Ic set Oo Fl a Ar attribute Oc Ns ... Oo Fl N Oc Oo Fl i Ar index Oc \
Oo Fl b Ar startsec Oc
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.
The
.Fl N
option causes any existing attributes to be cleared before adding new ones.
If the
.Fl N
option is given, and no
.Fl a
options 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
.Dq biosboot
flag is used to indicate which partition should be booted
by legacy BIOS boot code.
See the
.Cm biosboot
command for more information.
The
.Dq bootme
flag is used to indicate which partition should be booted
by the
.Nx 
UEFI boot code.
If not set on any partition, the first (in terms of partition index)
FFS partition located will be used.
The other boot* attributes are for compatibility with
.Fx
and are not currently used by
.Nx .
.Po
They may be used by
.Nx
in the future.
.Pc
.\" ==== show ====
.Pp
.It Nm Ic show Oo Fl AagHhlpuwx Oc \
Oo Fl i Ar index Oc \
Oo Fl b Ar startsec Oc \
Oo Fl W Ar width Oc
The
.Ic show
command displays the current partitioning on the listed device and gives
an overall view of the disk contents.
.Pp
There are three output variants, each of which is available in
a form intended for human viewing, and another for machine parsing.
The formats for some of the data for human viewing can be varied
by several of the options.
.Pp
The
.Fl W
option allows the desired output width, for human output, to be set.
It defaults to the value of the
.Ev COLUMNS
environment variable,
if set,
otherwise the width of the output terminal device,
if available.
If the width has still not been obtained,
then it will default to 80,
unless the
.Fl w
option is given,
causing 120 columns to be used instead.
Repeating
.Fl w
in this case will generate even wider output
.Pq up to a point .
The output width is not used as much as it perhaps could be,
and in no case will cause truncation of output,
which will exceed the specified width if required.
.Pp
The first output variant provides an overall summary of
the partitioning of the specified
.Ar device .
It is produced when none of the
.Fl a ,
.Fl b
or
.Fl i
options are used.
After a heading,
this format generates one line for each allocated partition,
for each gap between partitions,
and for the overhead sectors.
See the
.Sx OUTPUT FORMATS
section below for a complete description.
Each line contains the start block number,
the number of blocks,
and when a GPT user data partition is being listed,
its partition index,
and type \(en for other output lines,
their purpose.
Block numbers (start and size) are in units of the
.Ar device
sector size,
which can be viewed using the
.Nm
.Ic header
command.
.Pp
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.
The
.Fl l
and
.Fl u
options only have any effect on GPT partitions,
though
.Fl g
will also cause GPT header
.Dq partitions
to include the partition table's GUID,
and an MBR header to include its signature.
If more than one of those options are given,
.Fl l
takes precedence,
if the partition has a label,
then
.Fl g
and finally
.Fl u . 
Specifying more than one of those options can allow variations
in the output depending upon what data is available.
.Pp
With the
.Fl p
option this output is produced in a parsable format,
with no header.
See
.Sx OUTPUT FORMATS
below for the details.
.Pp
With the 
.Fl i
or the
.Fl b
option,
all the details of the particular GPT partition selected
will be displayed.
The format of this display remains subject to change.
When the
.Fl p
option is also given,
the format is more stable,
and always consists of a sequence of lines
each beginning with a keyword,
followed by a colon and a space,
and then the associated data value,
terminated by a newline character.
Note that only GPT user data partitions can be viewed this way,
that is partitions with an index greater than 0.
See the
.Sx OUTPUT FORMATS
section below for the details.
.Pp
With the
.Fl a
option,
all information for all partitions 
.Pq also including the headers and gaps
will be printed.
When used together with
.Fl p
the output is a sequence of blocks of output as would
be generated for
.Fl p Fl i
or
.Fl p Fl b
each followed by a blank line signifying the end of that
partition's data.
Similar data blocks for gaps and header information are
included,
with the
.Cm Index
shown as 0.
In each case,
the partitions are shown in the order of increasing values
of the
.Cm Start
field.
.Pp
The format for presentation to humans of the start and size
information can be modified by the
.Fl A ,
.Fl H ,
.Fl h
and
.Fl x
options.
The
.Fl x
option prints start/size in hex, but is ignored if any of
the
.Fl A ,
.Fl H ,
.Fl h
or
.Fl p
options are also given.
The other three options
.Pq Fl AHh
give various forms of more human
digestible ways to view the start/size values, but are only
used when the
.Fl p
option is absent.
The
.Fl h
option decodes the start and size information into a
sequence of values which,
when summed,
produce the original simple numeric sector count value,
multiplied by the sector size,
that is,
the number of bytes.
Each of these values is followed by a scaling indicator,
where only non-zero multiples of the scale indicated are included.
The scaling indicators are
.Po
in order in which they would be presented,
descending order of scale magnitude
.Pc
.Cm E
2^60,
.Cm P
2^50, 
.Cm T
2^40,
.Cm G
2^30,
.Cm M
2^20,
.Cm K
2^10,
and
.Cm B
2^0 (1).
.Pp
The
.Fl A
option instead uses
.Xr humanize_number 3
to present start block numbers and sizes as a rounded
approximation to the actual value,
as measured in bytes (not sectors),
at a suitable scale.
.Pp
And least (in all respects) the
.Fl H
option causes the output from
.Fl h
.Pq which is implied with Fl H
to be scaled in decimal,
rather than binary,
units,
so
.Cm K
is 10^3 instead of 2^10,
and
.Cm G
is 10^9 instead of 2^30,
etc.
This can be combined with
.Fl A .
.Pp
The order of precedence for the main options is:
.Fl a ,
.Fl b ,
.Fl i ,
.Fl l ,
.Fl g ,
.Fl u .
The
.Fl b
option will be ignored if no partition starting at
the given
.Ar startsec
is located.
.Pp
The
.Fl p
option can be combined with any of the above.
However the
.Fl A ,
.Fl H
and
.Fl h
options have no effect when
.Fl b ,
.Fl i ,
or
.Fl p
are given,
and only a very limited effect with
.Fl a
.Po the start and size columns are not affected,
but additional information is included with the
.Dq Size:
output data for GPT user partitions
.Pc .
The
.Fl x
option is only used when none of the
.Fl A ,
.Fl b ,
.Fl H ,
.Fl h ,
.Fl i ,
and
.Fl p
options are given.
.\" ==== type ====
.Pp
.It Nm Ic type Fl l
.It Nm Ic type Fl a 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
.Pp
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
.Ar newtype
specifies the UUID for the desired partition type,
or an alias, for a type known by
.Nm .
The
.Fl l
flag lists available types,
some of which are shown above with the
.Cm add
command.
.\" ==== unset ====
.Pp
.It Nm Ic unset Fl l
.It Nm Ic unset Fl a Ar attribute Oo Fl a Ar attribute Oc Ns ... \
Oo Fl i Ar index Oc Oo Fl b Ar startsec Oc
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 as indicated for the
.Nm
.Cm set
command.
.\" ==== uuid ====
.Pp
.It Nm Ic uuid Fl a Oc Fl U Ar newuuid 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
.Pp
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
general option
.Pc .
If
.Fl a
is used, then all partitions are updated,
and 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 OUTPUT FORMATS
When the
.Fl p
option is used with the
.Nm
.Cm show
command, the output is intended to be parsable by other code,
including perhaps GUI applications,
intending to manipulate GPT partition tables, and using
.Nm
as a backend to do the actual manipulation.
.Pp
The most basic format is that used with the
.Fl i
or
.Fl b
options to the
.Cm show
command.
This provides output about a single partition.
The output is a series of lines, each beginning with a
keyword, followed by a colon
.Pq Sq \&:
and a space.
The data associated with the keyword is the whole remainder of
the line, up to (not including) the terminating newline
.Pq Sq \en
character.
The following lines may be output, fields for which no data
exists are omitted.
Additional fields beyond those listed here may also be included.
It is generally safe to ignore an unknown keyword, and its data.
.Bl -tag -width 5m -offset indent -compact
.It Index
The (1 based) index number of the partition description in the GPT table.
This can be 0 only when this format is used with the
.Nm
.Cm show
.Fl a
.Fl p
command.
.It Start
An unsigned decimal integer giving the sector number of the
first data block of the partition.
.It Size
An unsigned decimal integer giving the number of sectors in the partition.
This must be greater than zero.
.It GUID
The partition's unique identifier in standard GUID format (hexadecimal
digits used).
.It TypeID
Gives the UUID which defines the intended use of the partition.
.It Type
Gives the short alias for the
.Ic TypeID
used by
.Nm ,
if one exists.
.It Long_Type
Gives a longer, more descriptive, name, if known, for the
.Ic TypeID .
.It Attributes
Lists any attributes set for the partition.
Attributes known by
.Nm
are shown first, as names, separated by a comma and space.
Any unknown attributes set are displayed last, enclosed in brackets
.Po
.Sq \&[
and
.Sq \&]
.Pc
as a hexadecimal string,
each enclosed character representing 4 attribute bits,
where each bit set represents one of the
possible 64 attributes which is applied to the partition.
Leading
.Sq 0
characters are omitted.
Note that the higher order 16 bits (the leftmost) have meanings
which depend upon the
.Ic TypeID .
The other 48 bits are common to all partition types.
.It Label
Gives the value of the GPT
.Dq name
field of the partition.
This is up to 36 characters, which may include any character
except NUL
.Pq Sq \e0 .
Each character may be any Unicode character representable by
a 16 bit code point (except 0).
Spaces, newlines, etc., may form part of the label.
To allow this label to always appear, and be understood, on
one output line, the label is first converted to UTF-8 encoding,
and then further encoded as if by
.Xr vis 1
using the options VIS_CSTYLE\||\|VIS_OCTAL\||\|VIS_TAB\||\|VIS_NL.
.It Purpose
This field is used only when the
.Ic Index
is zero,
and hence only with output using the
.Fl a
option,
and indicates the reason that the disk blocks
indicated by
.Ic Start
and
.Ic Size
are listed.
If this is
.Dq Unused
then this set of blocks are not currently assigned,
and so are available to be made into one or more
partitions as required.
Other values are used to indicate various data necessary
for the GPT table itself,
or represent other,
non-GPT data,
from the
.Ar device .
.El
.Pp
When the
.Nm
.Cm show
.Fl a
.Fl p
command is used, the format is identical to that just described,
except that multiple data blocks are produced, each followed by
a blank line (including the last).
As well as the GPT partition blocks, with
.Ic Index
greater than zero, which the previous format produces,
this can also produce
.Ic "Index: 0"
entries.
These indicate blocks on the
.Ar device 
which are not (currently) used by any assigned partition,
and are are either available for allocation,
or overhead used by the GPT system,
or are something unrelated to GPT partitioning
.Pq probably best viewed by some other tool .
.Pp
When
.Nm
.Cm show
.Fl p
is used without any of the
.Fl a ,
.Fl b
or
.Fl i
options, a summary of the entire GPT table is produced, with much
the same data (and number of entries) as when
.Fl a
is used, but in a condensed, one line per block, format.
Each output line starts with 3 numeric fields, each followed
by a single space.
Those are the values from the
.Ic Start ,
.Ic Size
and
.Ic Index
fields as described above, and as with
.Fl a
output, zero can occur as the index.
Those fields are followed by the string
.Dq GPT\ part\ \(en\ \&
for all partitions where the
.Ic Index
is not zero.
The contents of the remainder of the line depend upon
which, if any, of the
.Fl g ,
.Fl l
or
.Fl u
options are given.
With none of those options, the value from the
.Ic Long_Type
field is appended.
If the
.Fl l
option is used, the
.Ic Label
field is appended, otherwise if the
.Fl g
option is used, the
.Ic GUID
field is appended, otherwise the
.Fl u
option must have been used, and the
.Ic TypeID
field is appended.
.Pp
Lines with
.Ic Index
zero are similar, except after the 0 for the index, and its
following space, the
.Ic
Purpose
field is appended.
Additional data might follow that, depending upon the particular purpose.
GPT header fields will include the
.Ic GUID
if
.Fl g
was used.
A
.Dq PMBR
field will indicate
.Dq Pq active
if the active bit is set.
MBR partition entries will show the MBR partition type,
plus
.Dq Pq active
if appropriate.
.Pp
When
.Fl p
is not used, the
.Nm
.Cm show
command produces similar output to that described above,
in a less rigorous format,
more suitable for human consumption,
and more likely alter from time to time.
In this case the
.Ic Label
when output (as a sequence of UTF-8 characters) is not further encoded,
so may have effects upon the terminal,
and might occupy multiple lines.
.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.
Otherwise the exit status is 0 when no error has occurred,
and non-zero if an error prevented the command from executing correctly.
.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.
.Bd -literal
example# gpt label -a -l '' device
.Ed
.Pp
will clear all the GPT labels on the device.
.Bd -literal
example# gpt label -L '' -l Unlabeled device
.Ed
.Pp
will label all unlabeled partitions as
.Dq Unlabeled .
.Pp
For experimenting,
ordinary files can be used as devices:
.Bd -literal
fantasy$ gpt -m128T -s8k create -p 8064 ./BIGGEST
fantasy$ gpt -s8k show -A ./BIGGEST
  start     size  index  contents
      0     8.0K         PMBR
   8.0K     8.0K         Pri GPT header
    16K     1.0M         Pri GPT table
   1.0M     128T         Unused
   128T     1.0M         Sec GPT table
   128T     8.0K         Sec GPT header
fantasy$ ls -l BIGGEST
-rw-r--r--  1 user  staff  140737488355328 Feb  8 18:31 BIGGEST
fantasy$ du -h BIGGEST
2.1M    BIGGEST
.Ed
.Pp
The kernel limits the absolute apparent size of a file,
depending upon file system characteristics,
though the actual space used by
.Nm ,
is not all that significant.
This allows experimenting with Christmas wishes.
.Po
A filesystem this big, can currently, in 2026, actually
be created by building a Raid Level 5 from 6 or more of
the biggest drives available, or a Raid Level 0 (or ccd)
from 5 or more of them.
So, if you are nice, rather than naughty, your wish may be
granted.
.Pc
.Pp
Some examples of different output formats from
.Nm
.Cm show
follow:
.Bd -literal
oldstyle$ gpt show -l sd0
       start          size  index  contents
           0             1         PMBR
           1             1         Pri GPT header
           2            32         Pri GPT table
          34          2014         Unused
        2048        817152      1  GPT part - EFI
      819200       3325952      2  GPT part - Root
     4145152         49152      3  GPT part - Exchange
     4194304    2141192192      4  GPT part - Raid_C0
  2145386496       2095104      5  GPT part - Example
Multiline
Label
  2147481600          2016         Unused
  2147483616            32         Sec GPT table
  2147483648             1         Sec GPT header

newstyle$ gpt show -l -h sd0
            start     size  index  contents
                0     512B         PMBR
             512B     512B         Pri GPT header
               1K      16K         Pri GPT table
              17K    1007K         Unused
               1M     399M      1  GPT part - EFI
             400M  1G 600M      2  GPT part - Root
         1G 1000M      24M      3  GPT part - Exchange
               2G    1021G      4  GPT part - Raid_C0
            1023G    1023M      5  GPT part - Example
Multiline
Label
      1023G 1023M    1008K         Unused
1023G 1023M 1008K      16K         Sec GPT table
               1T     512B         Sec GPT header

friendly$ gpt show -l -A sd0
  start     size  index  contents
      0     512B         PMBR
   512B     512B         Pri GPT header
   1.0K      16K         Pri GPT table
    17K     1.0M         Unused
   1.0M     399M      1  GPT part - EFI
   400M     1.6G      2  GPT part - Root
   2.0G      24M      3  GPT part - Exchange
   2.0G     1.0T      4  GPT part - Raid_C0
   1.0T     1.0G      5  GPT part - Example
Multiline
Label
   1.0T     1.0M         Unused
   1.0T      16K         Sec GPT table
   1.0T     512B         Sec GPT header

parsable$ gpt show -l -p sd0
0 1 0 PMBR
1 1 0 Pri GPT header
2 32 0 Pri GPT table
34 2014 0 Unused
2048 817152 1 GPT part - EFI
819200 3325952 2 GPT part - Root
4145152 49152 3 GPT part - Exchange
4194304 2141192192 4 GPT part - Raid_C0
2145386496 2095104 5 GPT part - Example\enMultiline\enLabel
2147481600 2016 0 Unused
2147483616 32 0 Sec GPT table
2147483648 1 0 Sec GPT header

oldstyle$ gpt show -i5 sd0
Details for index 5:
Start: 2145386496 (1T)
Size: 2095104 (1G)
Type: ffs (49f48d5a-b10e-11dc-b99b-0019d1879648)
GUID: 63033daa-cc31-4b14-84c9-484669f3d199
Label: Example
Multiline
Label
Attributes: None

parsable$ gpt show -p -i 5 sd0
Index: 5
Start: 2145386496
Size: 2095104
GUID: 63033daa-cc31-4b14-84c9-484669f3d199
TypeID: 49f48d5a-b10e-11dc-b99b-0019d1879648
Type: ffs
Long_Type: NetBSD FFSv1/FFSv2
Label: Example\enMultiline\enLabel
.Ed
.Sh SEE ALSO
.Xr vis 1 ,
.Xr humanize_number 3 ,
.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.
.Pp
The biggest bug is that the BUGS section doesn't actually
mention any actual bugs.

.