GPT(8)

NAME
gpt - GUID partition table maintenance utility

SYNOPSIS
gpt [-Hnqrv] [-m mediasize] [-s sectorsize] [-T timestamp] command [command_options] device
gpt set -l
gpt unset -l
gpt type -l

DESCRIPTION
The gpt utility provides the necessary functionality to manipulate GUID partition tables (GPTs), but see 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 device is either a special file corresponding to a disk-like device or a regular file. The command is applied to each device listed on the command line.

  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.

-H  Ignore existing MBR (Hybrid MBR/GPT mode).

-m mediasize
    Override the default media size for the device (obtained from the kernel if possible) or defaulting to the file size for plain files.

-n  Do not update the wedge information that gpt changed. You need to use the dkctl(8) command to manually update the device's wedge configuration if you do that.

-q  Do not print error messages. This is not implemented completely yet.

-r  Open the device for reading only. Currently this option is primarily useful for the show command, but the intent is to use it to implement dry-run behaviour.

-s sectorsize
    Override the default sector size for the device (obtained from the kernel if possible) or 512 for plain files.

-T 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.

-v  Controls the verbosity level. The level increases with every occurrence of this option. There is no formalized definition of the different levels yet.

  Commands

gpt add [-a alignment] [-b blocknr] [-i index] [-l label] [-s size] [-t type]
    The 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.

    The -a 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. gpt will attempt to align the partition.

    The -b 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.

    The -i 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.

    The -l label option allows the user to specify a label for the partition.

    The -s size option allows the user to specify the size of the partition. If there is no suffix, or the suffix is ‘s’ or ‘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 ‘b’ to denote bytes, ‘k’ to denote kilobytes, ‘m’ to denote megabytes, ‘g’ to denote gigabytes, ‘t’ to denote terabytes, ‘p’ to denote petabytes, and ‘e’ to denote exabytes. The minimum size is 1 sector.

    The -t type option allows the user to specify the partition type. The type is given as a UUID, but gpt accepts
    apple
        Apple HFS
    apple-ufs
        Apple UFS
    bios
        BIOS Boot
    efi EFI System
    fbsd-legacy
        FreeBSD legacy
    fbsd-swap
        FreeBSD swap
    fbsd-ufs
        FreeBSD UFS/UFS2
    fbsd-vinum
        FreeBSD vinum
    zfs FreeBSD, NetBSD ZFS
    linux-data
        Linux data
    linux-raid
        Linux RAID
    linux-swap
        Linux swap
    linux-lvm
        Linux LVM
    obsd
        OpenBSD data
    windows
        Microsoft basic data - NTFS, FAT32 ("msdos"), FAT16, also used for UDF
    windows-reserved
        Microsoft reserved
    ccd NetBSD ccd component
    cgd NetBSD Cryptographic Disk
    ffs NetBSD FFSv1/FFSv2
    lfs NetBSD LFS
    raid
        NetBSD RAIDFrame component
    swap
        NetBSD swap
    as aliases for the most commonly used partition types.

gpt backup [-o outfile]
    The backup command dumps the MBR or (PMBR) and GPT partition tables to standard output or to a file specified by the outfile argument in a format to be used by the restore command. The format is a plist. It should not be modified.

gpt biosboot [-A] [-c bootcode] [-b startsec] [-i index] [-L label]
    The biosboot command allows the user to configure the partition that contains the primary bootstrap program, used during boot(8).

    The -A options sets the PMBR partition active. This should not normally be necessary, but some firmware might require it. If -A is omitted, the active flag will be cleared from the PMBR label.

    The -c option allows the user to specify the filename from which gpt should read the bootcode. The default is to read from /usr/mdec/gptmbr.bin.

    The partition that should contain the primary bootstrap code, (similar to that installed via installboot(8)) is selected using the -i, -L and -b options. One of these three options is required. The -i option selects the partition given by the index. The -L option selects the partition by label. If there are multiple partitions with the same label, the first one found will be used. The -b option selects the partition starting at block startsec.

gpt create [-AfP] [-p partitions]
    The 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 -f option. If the -f option is specified, an existing MBR is destroyed and any partitions described by the MBR are lost.

    The -A options sets the PMBR partition active.

    The -P option tells gpt to create only the primary table and not the backup table. This option is only useful for debugging and should not be used otherwise.

    The -p option changes the default number of partitions the GPT can accommodate. This is used whenever a new GPT is created. By default, the gpt utility will create space for 128 partitions (or 32 sectors of 512 bytes).

gpt destroy [-r]
    The destroy command allows the user to destroy an existing, possibly not empty GPT.

    The -r option instructs gpt to destroy the table in a way that it can be recovered.

gpt header
    The header command displays size information about the media and information from the GPT header if it exists.

gpt label [-a] <-f file | -l label>

gpt label [-b blocknr] [-i index] [-L label] [-s sectors] [-t type] <-f file | -l label>
    The label command allows the user to label any partitions that match the selection. At least one of the following selection options must be specified.

    The -a option specifies that all partitions should be labeled. It is mutually exclusive with all other selection options.

    The -b blocknr option selects the partition that starts at the given block number.

    The -i index option selects the partition with the given partition number.

    The -L label option selects all partitions that have the given label. This can cause multiple partitions to be relabeled.

    The -s sectors option selects all partitions that have the given size. This can cause multiple partitions to be labeled.

    The -t type option selects all partitions that have the given type. The type is given as a UUID or by the aliases that the add command accepts. This can cause multiple partitions to be labeled.

    The -f file or -l label options specify the new label to be assigned to the selected partitions. The -f 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 (-), the label is read from the standard input. The -l label option is used to specify the label in the command line. The label is assumed to be encoded in UTF-8.

gpt migrate [-Afs] [-p partitions]
    The 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 -f option. Specifying the -f option will cause unknown partitions to be ignored and any data in it to be lost.

    The -A options sets the PMBR partition active.

    The -s option prevents migrating BSD disk labels into GPT partitions by creating the GPT equivalent of a slice. Note that the -s option is not applicable to NetBSD partitions.

    The -p option changes the default number of partitions the GPT can accommodate. This is used whenever a new GPT is created. By default, the gpt utility will create space for 128 partitions (or 32 sectors of 512 bytes).

    The 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 (which takes one sector) and the GPT partition table. See the -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.

gpt recover
    The 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.

gpt remove [-a]

gpt remove [-b blocknr] [-i index] [-L label] [-s sectors] [-t type]
    The remove command allows the user to remove any and all partitions that match the selection. It uses the same selection options as the label command. See above for a description of these options. Partitions are removed by clearing the partition type. No other information is changed.

gpt resize [-i index] [-b startsec] [-a alignment] [-s size] [-q]
    The 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 -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 ‘s’ or ‘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 ‘b’ to denote bytes, ‘k’ to denote kilobytes, ‘m’ to denote megabytes and ‘g’ to denote gigabytes. The minimum size is 1 sector. If the -a option is specified then the size will be adjusted to be a multiple of alignment if possible. If the -q option is specified then the utility will not print output when a resize is not required.

gpt resizedisk [-s size] [-q]
    The 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 (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.

    The -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 ‘s’ or ‘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 ‘b’ to denote bytes, ‘k’ to denote kilobytes, ‘m’ to denote megabytes and ‘g’ to denote gigabytes. Using the -s option allows you to move the backup copy prior to resizing the medium. This is primarily useful when shrinking the medium. If the -q option is specified then the utility will not print output when a resize is not required.

gpt restore [-F] [-i infile]
    The restore command restores a partition table that was previously saved using the backup command. The partition table is read from standard input or a file specified in the infile argument and is expected to be in the format of a plist. It assumes an empty disk. The -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 restore will automatically adjust. However, the new disk must use the same sector size as the old disk.

gpt set [-a attribute] [-N] [-i index] [-b startsec]

gpt set -l
    The set command sets various partition attributes. The -l flag lists all available attributes. The -a option specifies which attributes to set and may be specified more than once, or the attributes can be comma-separated. If the -N option and no -a option are specified, all attributes are removed. The -i or the -b option specify which entry to update. The possible attributes are “biosboot”, “bootme”, “bootonce”, “bootfailed”, “noblockio”, and “required”. The biosboot flag is used to indicate which partition should be booted by legacy BIOS boot code. See the 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 FreeBSD and are not currently used by NetBSD. They may be used by NetBSD in the future.

gpt show [-aglux] [-i index] [-b startsec]
    The show command displays the current partitioning on the listed devices and gives an overall view of the disk contents. With the -g option the GPT partition GUID will be displayed instead of the GPT partition type. With the -l option the GPT partition label will be displayed instead of the GPT partition type. With the -u option the GPT partition type is displayed as a UUID instead of in a user friendly form. With the -i or the -b option, all the details of a particular GPT partition will be displayed. The format of this display is subject to change. With the -a option, all information for all GPT partitions (just like with -i index) will be printed. The -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: -a, -i, -l, -g, -u, -x.

gpt type [-a] -T newtype

gpt type [-b blocknr] [-i index] [-L label] [-s sectors] [-t type] -T newtype

gpt type -l
    The 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 label command. See above for a description of these options. The -l flag lists available types.

gpt unset -a attribute [-i index] [-b startsec]

gpt unset -l
    The unset command unsets various partition attributes. The -l flag lists all available attributes. The -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 -i or the -b option specifies which entry to update. The possible attributes are “biosboot”, “bootme”, “bootonce”, “bootfailed”, “noblockio”, and “required”. The biosboot flag is used to indicate which partition should be booted by legacy BIOS boot code. See the biosboot command for more information. The other attributes are for compatibility with FreeBSD and are not currently used by any NetBSD code. They may be used by NetBSD code in the future.

gpt uuid [-a]

gpt uuid [-b blocknr] [-i index file ...] [-L label] [-s sectors] [-t type] [-U newuuid]
    The 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 label command. See above for a description of these options. If newuuid is not specified, a random UUID value is derived from the timestamp (see the -T option). If -a is used, then the header UUID is changed as well.

    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.

EXIT STATUS
The gpt 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.

EXAMPLES

    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#

Booting from GPT on a BIOS system: this creates a bootable partition.

    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

Note that biosboot is not needed for UEFI systems.

SEE ALSO
boot(8), dkctl(8), fdisk(8), installboot(8), mount(8), newfs(8), swapctl(8)

HISTORY
The gpt utility appeared in FreeBSD 5.0 for ia64. gpt utility first appeared in NetBSD 5.0.

BUGS
The development of the gpt 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.

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.

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.