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.\" $OpenBSD: fdisk.8,v 1.126 2025/05/28 03:55:41 jsg Exp $ .\" .\" .\" Copyright (c) 1997 Tobias Weingartner .\" .\" Permission to use, copy, modify, and distribute this software for any .\" purpose with or without fee is hereby granted, provided that the above .\" copyright notice and this permission notice appear in all copies. .\" .\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF .\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR .\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES .\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. .\" .Dd $Mdocdate: May 28 2025 $ .Dt FDISK 8 .Os .Sh NAME .Nm fdisk .Nd partition table maintenance program .Sh SYNOPSIS .Nm fdisk .Op Fl evy .Op Fl A | g | i | u .Op Fl b Ar blocks Ns Op @ Ns Ar offset Ns Op : Ns Ar type .Op Fl l Ar blocks | Fl c Ar cylinders Fl h Ar heads Fl s Ar sectors .Op Fl f Ar file .Ar disk .Nm fdisk .Fl R .Op Fl y .Ar disk Op Ar file .Sh DESCRIPTION .Nm fdisk creates and edits MBR and GPT partition tables. These tables are used by the boot process of some platforms to find the .Ox kernel and, when present, are used by the kernel to find the .Xr disklabel 5 . .Pp Caution is advised when editing these tables since some platforms rely on specific configurations created at install time. .Pp The options are as follows: .Bl -tag -width Ds .It Fl A Modifies the GPT partition table entries on .Ar disk to put all available space not taken by .Fl b into a single .Ox partition. The available space is maximized by deleting all existing partition entries except for partition types APFS ISC, APFS, APFS Recovery, BIOS Boot, HiFive FSBL, HiFive BBL and partitions with the .Sq Required GPT attribute set. .Pp If APFS ISC, APFS, or APFS Recovery partitions are detected then existing EFI system partitions are also preserved. If the preserved EFI system partition has fewer blocks than the number requested with .Fl b , the modified GPT is discarded. .It Fl b Ar blocks Ns Op @ Ns Ar offset Ns Op : Ns Ar type Creates a partition table entry of the specified number of blocks, offset and type. .Ar offset defaults to the first available block, and .Ar type defaults to .Sq EF . .Pp .Fl b is only available in combination with .Fl A , .Fl g , or .Fl i . .Pp If .Fl A or .Fl g is specified, only the .Ar blocks value is used. .It Xo .Fl c Ar cylinders .Fl h Ar heads .Fl s Ar sectors .Xc Specifies a geometry for .Nm to use. By default the disk size and geometry are obtained from the default .Xr disklabel 5 constructed by the kernel for .Ar disk . See .Xr disklabel 5 and .Xr disklabel 8 . .It Fl e Invokes the interactive partition table editor. See .Sx COMMAND MODE below. .It Fl f Ar file Specifies a file containing the bootcode for an MBR. The default file is .Pa /usr/mdec/mbr . .It Fl g Writes a default GPT, including a protective MBR, to .Ar disk . The GPT has a single .Ox partition containing all available space not taken by .Fl b . .It Fl i Writes a default MBR to .Ar disk . The MBR has a single .Ox partition containing all the available space not taken by .Fl b . The bootcode is initialized as described in .Fl u . .It Fl l Ar count Treat .Ar disk as though it has a size of .Ar count blocks. .It Fl R Ar disk Op Ar file Creates a GPT or MBR partition table based on the contents of .Ar file . .Ar file contains the output of .Nm Fl v (e.g. the fdisk* files in /var/backups) or compact GPT partition descriptions of the form .Pp .Dl <id>:<type>[<start>:<size>]<attributes><name> .Pp where a new partition UUID is always generated and <attributes><name> is optional. For example: .Pp .Dl 0: EFI Sys [64:66560] 0x0 EFI System Area .Pp If <start> is 0 it is set to the first usable LBA of the largest chunk of free space. .Pp If .Ar file is not provided, .Nm attempts to fully restore a GPT if either a primary or secondary GPT exists on .Ar disk . .It Fl u Updates the MBR bootcode. If a bootcode file is present (see .Fl f ) the MBR, except for the partition entries, is replaced by the first block of the file. If no bootcode file is present, zeros are used. .Pp Not available when editing a GPT. .It Fl v Prints detailed information about the MBR, the Primary GPT and the Secondary GPT. .It Fl y New or modified partition table is written to disk without asking for confirmation. .It Ar disk .Nm creates or modifies the partition table of .Ar disk . .Ar disk can be a full pathname, e.g. .Pa /dev/rsd0c , a raw partition name, e.g. .Pa sd0c , or just the disk name, e.g. .Pa sd0 . .El .Sh TYPICAL LAYOUT When called without options, .Nm prints the partition table of .Ar disk . .Pp If .Ar disk has a GPT a terse version of its contents is printed: .Bd -literal -offset 1n # fdisk sd0 Disk: sd0 Usable LBA: 64 to 500118128 [500118192 Sectors] #: type [ start: size ] ------------------------------------------------------------------------ 1: EFI Sys [ 64: 960 ] 3: OpenBSD [ 1024: 500117105 ] .Ed .Pp When .Ar disk does not have a GPT, the first block of .Ar disk is printed as an MBR: .Bd -literal -offset 1n # fdisk sd0 Disk: sd0 geometry: 121601/255/63 [1953525168 Sectors] Offset: 0 Signature: 0xAA55 Starting Ending LBA Info: #: id C H S - C H S [ start: size ] ------------------------------------------------------------------------ 0: 0B 0 1 1 - 26108 0 63 [ 63: 419425020 ] FAT32 1: 00 0 0 0 - 0 0 0 [ 0: 0 ] unused 2: 00 0 0 0 - 0 0 0 [ 0: 0 ] unused *3: A6 26108 1 1 - 121600 254 63 [ 419425083: 1534094982 ] OpenBSD .Ed .Pp .Em NOTE : Partition entry #3 of this MBR is flagged as bootable. .Pp .Em NOTE : The .Em S field in the C/H/S values is .Dq 1 based , but the LBA "start" field is .Dq 0 based . .Pp The .Fl v option causes more information to be printed: .Bd -literal -offset 1n # fdisk -v sd0 Primary GPT: Disk: sd0 Usable LBA: 64 to 500118128 [500118192 Sectors] GUID: f0418899-4976-4604-a783-3ebe135a8f12 #: type [ start: size ] guid name ------------------------------------------------------------------------ 1: EFI Sys [ 64: 960 ] d0834013-dab8-44df-a5e4-123148f17e03 EFI System Area 3: OpenBSD [ 1024: 500117105 ] cd356d77-8369-44b4-996e-79e8b9a47bfe OpenBSD Area Secondary GPT: Disk: sd0 Usable LBA: 64 to 500118128 [500118192 Sectors] GUID: f0418899-4976-4604-a783-3ebe135a8f12 #: type [ start: size ] guid name ------------------------------------------------------------------------ 1: EFI Sys [ 64: 960 ] d0834013-dab8-44df-a5e4-123148f17e03 EFI System Area 3: OpenBSD [ 1024: 500117105 ] cd356d77-8369-44b4-996e-79e8b9a47bfe OpenBSD Area MBR: Disk: sd0 geometry: 31130/255/63 [500118192 Sectors] Offset: 0 Signature: 0xAA55 Starting Ending LBA Info: #: id C H S - C H S [ start: size ] ------------------------------------------------------------------------------- 0: EE 0 0 2 - 31130 233 63 [ 1: 500118191 ] EFI GPT 1: 00 0 0 0 - 0 0 0 [ 0: 0 ] unused 2: 00 0 0 0 - 0 0 0 [ 0: 0 ] unused 3: 00 0 0 0 - 0 0 0 [ 0: 0 ] unused .Ed .Sh COMMAND MODE When .Nm enters interactive command mode, it copies the partition table from .Ar disk into memory and performs all edits on that copy. The partition table on .Ar disk is modified only by .Em write or .Em quit commands. .Pp The prompt contains information about the state of the edit process. .Pp .Dl Ar disk Ns *:1> .Pp Where .Ar disk is the name of the disk being edited, .Sq * means that the partition table has been modified, but not yet written to disk and 1 is the edit level when operating on the MBR or GPT. This number is 2 when editing an extended partition in the MBR, 3 when editing an extended partition within the edit level 2 extended partition, and so on. .Pp The list of commands and their functions is given below. Commands may be abbreviated. The first command matching the abbreviation is selected. .Bl -tag -width Ds .It Cm ?\& A synonym for .Cm help . .It Cm help Displays a short summary of available commands. .It Cm manual Displays this manual page. .It Cm reinit Op Cm gpt | Cm mbr Initializes the partition table. .Pp By default an MBR partition table is initialized. If .Cm gpt is specified a GPT partition table is initialized, including the protective MBR. .It Cm setpid Ar # Sets the identifier of the partition table entry. .It Cm edit Ar # Edit an entry in the partition table. The offset and size of the entry may be specified in CHS mode (MBR only), by using sector offsets and sizes, or by using the units .Sq b , .Sq k , .Sq m , .Sq g , or .Sq t to indicate bytes, kilobytes, megabytes, gigabytes, or terabytes. The special size value .Sq * causes the partition to be sized to use the remainder of the disk. .It Cm flag Ar # Op Ar value Set the partition's flag (MBR) or attribute (GPT) value. .Ar value can be a positive integer or a hex string. An MBR partition will accept values from 0 to 0xff. A GPT partition will accept values from 0 to 0xfffffffffffffff. If .Ar value is not provided, the partition's bootable flag is set and all other partitions have their bootable flags reset. MBR partitions with the bootable flag set are printed with a .Sq * prefix. GPT partitions with the bootable flag set display 'bootable' in their attributes list. .It Cm update Updates the MBR bootcode. If a bootcode file is present (see .Fl f ) the MBR, except for the partition entries, is replaced by the first block of the file. If no bootcode file is present, zeros are used. .Pp Not available when editing a GPT. .It Cm select Ar # Selects an extended partition entry, increasing the edit level by 1. .Pp Not available when editing a GPT. .It Cm swap Ar # Ar # Swaps two partition entries. .It Cm print Op Ar unit Prints the partition table. If .Ar unit is .Sq b , .Sq k , .Sq m , .Sq g , or .Sq t partition sizes are shown in bytes, kilobytes, megabytes, gigabytes, or terabytes. If .Ar unit is not provided, sizes are shown in sectors. .It Cm write Writes the partition table to disk. .It Cm exit Discards outstanding changes and exits the current edit level. If the edit level is 1, .Nm terminates. .It Cm quit Writes outstanding changes to disk and exits the current edit level. If the edit level is 1, .Nm terminates. .It Cm abort Discards outstanding changes and terminates .Nm . .El .Sh FILES .Bl -tag -width /usr/mdec/mbr -compact .It Pa /usr/mdec/mbr default MBR bootcode .El .Sh SEE ALSO .Xr disklabel 5 , .Xr boot 8 , .Xr boot_amd64 8 , .Xr boot_i386 8 , .Xr boot_macppc 8 , .Xr disklabel 8