Manual Pages for UNIX Darwin command on man fdisk

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

NAME

ffddiisskk - DOS partition maintenance program

SYNOPSIS

ffddiisskk [-iieeuu] [-ff mbrname] [-cc cylinders] [-hh heads] [-ss 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 partition table for an ``active'' parti-

tion (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:

-ii Initialize the MBR sector.

-aa style

Specify an automatic partitioning style.

-ee Edit existing MBR sectors.

-ff mbrname

Specifies an alternate MBR template file.

-uu Update MBR code, preserving existing partition table.

-yy Do not ask for confirmation before writing.

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

-rr Read a partition table from the standard input.

-tt Test if the disk is partitioned.

-cc cylinders, -hh heads, -ss sectors

Specifies an alternate BIOS geometry for ffddiisskk to use.

-SS size

Specify the disk size in blocks.

The DOS ffddiisskk program can be used to divide space on the disk into parti-

tions and set one active. This ffddiisskk 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 -cc, -hh, and -ss options. In the future, ffddiisskk

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 sys-

tems prefer the starting sector and size in preference to the CHS values.

The -ii flag is used to indicate that the partition data is to be initial-

ized. In this mode, ffddiisskk will completely overwrite the primary MBR and

partition table, either using the default MBR template, or the one speci-

fied by the -ff flag.

In the default template, partition number 1 will be configured as a Dar-

win 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 -aa 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 Darwin UFS partition (type A8 hex). ufs Makes the entire disk one HFS+ partition (type AF hex). dos Makes the entire disk one DOS partition (type 0C hex). raid Makes the entire disk one type AC hex partition.

The -uu flag is used to update the MBR code on a given drive. The MBR

code extends from offset 0x000 to the start of the partition table at

offset 0x1BE. It is similar to the -ii flag, except the existing parti-

tion 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 -uu and -ii flags may not be specified together.

The flag -ee is used to modify a partition table using a interactive edit

mode of the ffddiisskk 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 ffddiisskk asks you about writing out changes. CCOOMMMMAANNDD MMOODDEE 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 infor-

mation 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 parti-

tions. The list of commands and their explanations are given below.

help Display a list of commands that ffddiisskk understands in the interac-

tive 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 ffddiisskk 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 table 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 ffddiisskk, either returning to the previ-

ously selected in-memory copy of a boot block, or exiting the

program if there is none.

quit Exit the current level of ffddiisskk, either returning to the previ-

ously selected in-memory 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. NNOOTTEESS 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 ffddiisskk gives you an opportunity to change them if there is a need to. This allows the user to create a bootblock 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 partition. You should run this program interactively once or twice to see how it

works. This is completely safe as long as you answer the ``write'' ques-

tions in the negative. FILES /usr/mdec/mbr default MBR template

BUGS

There are subtleties ffddiisskk 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 Emptor. BSD January 3, 2002 BSD