FDISK

Section: Maintenance Commands (8)
Updated: Mar 30, 1993
Index Return to Main Contents

NAME

fdisk - examine or change DOS partitioning information

SYNOPSIS

/usr/etc/fdisk <raw-device> [ inquiry ] [ action ] [ flags ]

DESCRIPTION

fdisk displays or changes the DOS partition table found in the bootsector of i386 bootable disks. If no inquiry or action is specified, it is run in interactive mode, allowing multiple changes to the partition table to be made. If an inquiry is specified, the result is displayed to standard output but no changes to the partition table are made. If an action is requested, the partition table will usually be modified and fdisk immediately returns. When fdisk is run in interactive mode, no changes to the partition table are effected until the user explicitly writes the changes.

fdisk modifies only the bootsector and (unless the -bootsectorOnly flag is specified) the first sector of newly allocated partitions; it does not modify other contents of the disk in any way. However, it is used to redefine the allocation of the disk; deleting a partition makes the partition inaccessible and should be considered tantamount to erasing the partition.

Flags

-useAllSectors: For compatibility with the DOS version, fdisk by default recognizes only those sectors that are bios-accessible. However, if fdisk is passed the -useAllSectors flag, it will recognize all sectors physically present. Data allocated in the extra sectors may not be bios accessible, and certain fields in the partition table might overflow, which might cause problems with some operating systems. Bios inaccessible sectors could prevent NEXTSTEP from booting, though once booted NEXTSTEP is unaffected by bios limitations or partition table overflows.
-useBoot0: Reads in /usr/standalone/i386/boot0 to be used as the partition boot program. If this option is not specified, the existing boot program is retained.
-bootsectorOnly: Tells fdisk to modify only the bootsector when saving changes. Otherwise, the default behavior is to zero the first sector of newly-created partitions to ensure that extant data is not treated as a boot program or meaningful partition information.

Interactive mode

When fdisk is run in interactive mode, it displays the defined partitions and unallocated disk space, then displays a menu. Information on defined partitions includes:

Type: The type of data the partition is said to contain.
Start: The starting address of the partition, in megabytes.
Size: The size of the partition, in megabytes.
Status: If the partition is marked as active, the partition will be booted from when the selected device is the boot device.

All unused blocks on the disk are also displayed, with their sizes rounded to the nearest megabyte.

Interactive mode main menu options

Create a new partition: Allocates space on the disk for use by NEXTSTEP or another operating system. The space is allocated from the first adequate free block. The partition table structure only allows for 4 partitions per disk.
Delete partition: Deallocates the space occupied by the specified partition.
Set the active partition: Specifies which partition is to be booted from if the selected device is the boot device.
Show disk information: Displays the layout of the disk, both according to the driver and accoring to the rom bios. For compatibility with the DOS verstion, fdisk by default only recognizes those sectors that are bios-accessible. However, if fdisk is passed the -useAllSectors flag, it will recognize all sectors physically present.

Non-interactive mode

For the benefit of installation scripts, fdisk can be given one inquiry or one action to effect partitioning. Inquiries do not modify the partition table, but actions usually do.

The following inquiries are allowed:

-isDiskPartitioned

Outputs "Yes" if the disk contains 1 or more valid partitions, "No" otherwise.

-isThereExtendedPartition

Outputs "Yes" if the disk has a DOS extended partition, "No" otherwise.

-isThereNeXTPartition

Outputs "Yes" if the disk has a NEXTSTEP partition, "No" otherwise.

-freeSpace

Outputs the size (in megabytes) of the largest free block on the disk.

-freeWONeXT

Outputs the size (in megabytes) of the largest free block on the disk if the NEXTSTEP partition were deleted.

-freeWONeXTorExt

Outputs the size (in megabytes) of the largest free block on the disk if the NEXTSTEP and extended partitions were deleted.

-sizeofExtended

Outputs the size (in megabytes) of the extended partition.

-diskSize

Outputs the size of the disk in megabytes.

-installSize

Outputs the size that NEXTSTEP would install to on the current disk; effectively the size of the NEXTSTEP partition if the disk is partitioned, otherwise the size of the disk.

The following actions are allowed:

-removePartitioning: Zeros out the bootsector, eliminating the partition table and boot program. Prepares the disk so that NEXTSTEP will install on the entire disk.
-dosPlusNeXT <megsForDos>: Partitions the disk with <megsForDos> reserved for DOS and the remainder used for NEXTSTEP.
-setAvailableToNeXT: Deletes the current NEXTSTEP partition, then reserves the largest free space for NEXTSTEP; doesn't destroy other partitions.
-setExtAndAvailableToNeXT: Deletes the current NEXTSTEP and extended partitions, then reserves the largest free space for NEXTSTEP; doesn't destroy other partitions.
-setExtendedToNeXT: Changes the current extended partition to NEXTSTEP.
-setNeXTActive: Makes the NEXTSTEP partition active, but doesn't affect the size of any partition.

BUGS

When creating a partition, fdisk's idea of a megabyte is sometimes different than other versions; fdisk is not guaranteed to locate the partition where another version would.

fdisk knows nothing about logical partitions, which are sub-partitions of an extended partition. Nor perhaps should it, as these are gross kludges from the Evil OS Company of the North.

fdisk does not tolerate inconsistent partitions; a partition that overlaps another will not be included in the partition table when it is written out, and the cylinder/head/sector bios values are derived from the absolute sector numbers. Upon writing, the partition table entries are ordered the same as the actual partitions.