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OpenDarwin 7.2.1 - man page for fdisk (opendarwin section 8)

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FDISK(8)			   BSD System Manager's Manual				 FDISK(8)

NAME
     fdisk -- DOS partition maintenance program

SYNOPSIS
     fdisk [-ieu] [-f mbrname] [-c cylinders] [-h heads] [-s sectors] device

DESCRIPTION
     In order for the BIOS to boot the kernel, certain conventions must be adhered to.	Sector 0
     of a bootable hard disk must contain boot code, an MBR partition table, and a magic number
     (0xAA55).	These MBR partitions (also known as BIOS partitions) can be used to break the
     disk up into several pieces.

     The BIOS loads sector 0 of the boot disk into memory, verifies the magic number, and begins
     executing the code at the first byte.  The normal DOS MBR boot code searches the MBR parti-
     tion table for an ``active'' partition (indicated by a '*' in the first column), and if one
     is found, the boot block from that partition is loaded and executed in place of the original
     (MBR) boot block.

     The options are as follows:

     -i      Initialize the MBR sector.

     -a style
	     Specify an automatic partitioning style.

     -e      Edit existing MBR sectors.

     -f mbrname
	     Specifies an alternate MBR template file.

     -u      Update MBR code, preserving existing partition table.

     -y      Do not ask for confirmation before writing.

     -d      Dump partition table in a format readable by the -r option.

     -r      Read a partition table from the standard input.

     -t      Test if the disk is partitioned.

     -c cylinders, -h heads, -s sectors
	     Specifies an alternate BIOS geometry for fdisk to use.

     -S size
	     Specify the disk size in blocks.

     The DOS fdisk program can be used to divide space on the disk into partitions and set one
     active.  This fdisk program serves a similar purpose to the DOS program.  When called with
     no special flags, it prints the MBR partition table of the specified device, i.e.,

	 # fdisk fd0
	 Disk: fd0	 geometry: 80/2/18 [2880 sectors]
	 Offset: 0	 Signature: 0xAA55
		  Starting	  Ending
	  #: id  cyl  hd sec -	cyl  hd sec [	  start -	size]
	 ----------------------------------------------------------------------
	 *1: A6    0   0   1 -	 79   1  18 [	      0 -	2880] OpenBSD
	  2: 00    0   0   0 -	  0   0   0 [	      0 -	   0] unused
	  3: A7    0   0   2 -	 79   1  18 [	      1 -	2879] NEXTSTEP
	  4: 00    0   0   0 -	  0   0   0 [	      0 -	   0] unused

     The geometry displayed is a synthetic geometry unless another geometry has been selected
     using the -c, -h, and -s options.	In the future, fdisk will read the BIOS geometry from the
     IOKit registry.

     In this example, the disk is divided into two partitions that happen to fill the disk.  The
     first partition overlaps the third partition.  (Used for debugging purposes.)

     #		 Number of partition table entry.  A ``*'' denotes the bootable partition.

     id 	 System identifier.  OpenBSD reserves the magic number 166 decimal (A6 in hex).
		 If no 166 partition is found, it will use an older FreeBSD partition (with a
		 magic number of 165 or A5 in hex).

     cyl/hd/sec  These fields provide the starting and ending address of the partition in BIOS
		 geometry

     start/size  These fields provide the starting sector and size in sectors of the partition in
		 linear block addresses.

     NOTE: The sectors field is ``1 based'', and the start field is ``0 based''.  The CHS values
     may need to be in the BIOS's geometry for older systems to be able to boot and use the drive
     correctly; most modern systems prefer the starting sector and size in preference to the CHS
     values.

     The -i flag is used to indicate that the partition data is to be initialized.  In this mode,
     fdisk will completely overwrite the primary MBR and partition table, either using the
     default MBR template, or the one specified by the -f flag.

     In the default template, partition number 1 will be configured as a Darwin boot partition
     spanning from cylinder 0, head 1, sector 1, and extending for 8 megabytes.  Partition number
     2 will be configured as a Darwin HFS partition spanning the rest of the disk.  This mode is
     designed to initialize an MBR the very first time, or when it has been corrupted beyond
     repair.

     You can specify other default partition styles with the -a flag.  The available styles are:

     boothfs	 Creates an 8Mb boot partition (type AB hex) and makes the rest of the disk a
		 Darwin HFS partition (type AF hex).

     bootufs	 Creates an 8Mb boot partition (type AB hex) and makes the rest of the disk a
		 Darwin UFS partition (type A8 hex).

     hfs	 Makes the entire disk one HFS+ partition (type AF hex).

     ufs	 Makes the entire disk one Darwin UFS partition (type A8 hex).

     dos	 Makes the entire disk one DOS partition (type 0C hex).

     raid	 Makes the entire disk one type AC hex partition.

     The -u flag is used to update the MBR code on a given drive.  The MBR code extends from off-
     set 0x000 to the start of the partition table at offset 0x1BE.  It is similar to the -i
     flag, except the existing partition table is preserved. This is useful for writing new MBR
     code onto an existing drive, and is equivalent to the DOS command ``FDISK /MBR''.	Note that
     this option will overwrite the NT disk signature, if present.  The -u and -i flags may not
     be specified together.

     The flag -e is used to modify a partition table using a interactive edit mode of the fdisk
     program.  This mode is designed to allow you to change any partition on the drive you
     choose, including extended partitions.  It is a very powerful mode, but is safe as long as
     you do not execute the write command, or answer in the negative (the default) when fdisk
     asks you about writing out changes.

COMMAND MODE
     When you first enter this mode, you are presented with a prompt, that looks like so: fdisk:
     0>.  This prompt has two important pieces of information for you.	It will tell you if the
     in-memory copy of the boot block has been modified or not.  If it has been modified, the
     prompt will change to look like: fdisk:*0>.  The second piece of information pertains to the
     number given in the prompt.  This number specifies the disk offset of the currently selected
     boot block you are editing.  This number could be something different that zero when you are
     editing extended partitions.  The list of commands and their explanations are given below.

     help    Display a list of commands that fdisk understands in the interactive edit mode.

     manual  Display this manual page.

     reinit  Initialize the currently selected, in-memory copy of the boot block.

     auto    Partition the disk with one of the automatic partition styles.

     disk    Display the current drive geometry that fdisk has probed.	You are given a chance to
	     edit it if you wish.

     edit    Edit a given table entry in the memory copy of the current boot block.  You may edit
	     either in BIOS geometry mode, or in sector offsets and sizes.

     setpid  Change the partition identifier of the given partition table entry.  This command is
	     particularly useful for reassigning an existing partition to OpenBSD.

     flag    Make the given partition table entry bootable.  Only one entry can be marked
	     bootable.	If you wish to boot from an extended partition, you will need to mark the
	     partition table entry for the extended partition as bootable.

     update  Update the machine code in the memory copy of the currently selected boot block.
	     Note that this option will overwrite the NT disk signature, if present.

     select  Select and load into memory the boot block pointed to by the extended partition ta-
	     ble entry in the current boot block.

     print   Print the currently selected in-memory copy of the boot block and its MBR table to
	     the terminal.

     write   Write the in-memory copy of the boot block to disk.  You will be asked to confirm
	     this operation.

     exit    Exit the current level of fdisk, either returning to the previously selected in-mem-
	     ory copy of a boot block, or exiting the program if there is none.

     quit    Exit the current level of fdisk, either returning to the previously selected in-mem-
	     ory copy of a boot block, or exiting the program if there is none.  Unlike exit it
	     does write the modified block out.

     abort   Quit program without saving current changes.

NOTES
     The automatic calculation of starting cylinder etc. uses a set of figures that represent
     what the BIOS thinks is the geometry of the drive.  These figures are by default taken from
     the in-core disklabel, or values that /boot has passed to the kernel, but fdisk gives you an
     opportunity to change them if there is a need to.	This allows the user to create a boot-
     block that can work with drives that use geometry translation under a potentially different
     BIOS.

     If you hand craft your disk layout, please make sure that the OpenBSD partition starts on a
     cylinder boundary.  (This restriction may be changed in the future.)

     Editing an existing partition is risky, and may cause you to lose all the data in that par-
     tition.

     You should run this program interactively once or twice to see how it works.  This is com-
     pletely safe as long as you answer the ``write'' questions in the negative.

FILES
     /usr/mdec/mbr  default MBR template

SEE ALSO
     pdisk(8)

BUGS
     There are subtleties fdisk detects that are not explained in this manual page.  As well,
     chances are that some of the subtleties it should detect are being steamrolled.  Caveat Emp-
     tor.

BSD					 January 3, 2002				      BSD
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