fdisk(8)

NAME

fdisk - Partition table manipulator for Linux

SYNOPSIS

fdisk [ -l ] [ -v ] [ -s partition] [ device ]

DESCRIPTION

fdisk is a menu driven program for manipulation of the hard disk partition table. The device is usually one of the following:

/dev/hda
/dev/hdb
/dev/sda
/dev/sdb

The partition is a device name followed by a partition number. For example, /dev/hda1 is the first partition on the first hard disk in the system.
If possible, fdisk will obtain the disk geometry automatically. This is not necessarily the physical disk geometry, but is the disk geometry that MS-DOS uses for the partition table. If fdisk warns you that you need to set the disk geometry, please believe this statement, and set the geometry. This should only be necessary with certain SCSI host adapters (the drivers for which are rapidly being modified to provide geometry information automatically).
Whenever a partition table is printed out, a consistency check is performed on the partition table entries. This check verifies that the physical and logical start and end points are identical, and that the partition starts and ends on a cylinder boundary (except for the first partition).
Old versions of fdisk (all versions prior to 1.1r [including 0.93]) incorrectly mapped the cylinder/head/sector specification onto absolute sectors. This may result in the first partition on a drive failing the consistency check. If you use LILO to boot, this situation can be ignored. However, there are reports that the OS/2 boot manager will not boot a partition with inconsistent data.
Some versions of MS-DOS create a first partition which does not begin on a cylinder boundary, but on sector 2 of the first cylinder. Partitions beginning in cylinder 1 cannot begin on a cylinder boundary, but this is unlikely to cause difficulty unless you have OS/2 on your machine.
In version 1.1r, a BLKRRPART ioctl() is performed before exiting when the partition table is updated. This is primarily to ensure that removable SCSI disks have their partition table information updated. If the kernel does not update its partition table information, fdisk warns you to reboot. If you do not reboot your system after receiving such a warning, you may lose or corrupt the data on the disk. Sometimes BLKRRPART fails silently, when installing Linux, you should always reboot after editing the partition table.

DOS 6.x WARNING

The DOS 6.x FORMAT command looks for some information in the first sector of the data area of the partition, and treats this information as more reliable than the information in the partition table. DOS FORMAT expects DOS FDISK to clear the first 512 bytes of the data area of a partition whenever a size change occurs. DOS FORMAT will look at this extra information even if the /U flag is given -- we consider this a bug in DOS FORMAT and DOS FDISK.
The bottom line is that if you use cfdisk or fdisk to change the size of a DOS partition table entry, then you must also use dd to zero the first 512 bytes of that partition before using DOS FORMAT to format the partition. For example, if you were using cfdisk to make a DOS partition table entry for /dev/hda1, then (after exiting fdisk or cfdisk and rebooting Linux so that the partition table information is valid) you would use the command "dd if=/dev/zero of=/dev/hda1 bs=512 count=1" to zero the first 512 bytes of the partition. BE EXTREMELY CAREFUL if you use the dd command, since a small typo can make all of the data on your disk useless.
BE EXTREMELY CAREFUL if you use the dd command, since a small typo can make all of the data on your disk useless.
For best resutls, you should always use an OS-specific partition table program. For example, you should make DOS partitions with the DOS FDISK program and Linux partitions with the Linux fdisk or Linux cfdisk program.

OPTIONS

-v

Prints version number of fdisk program.

-l

Lists the partition tables for /dev/hda , /dev/hdb , /dev/sda , /dev/sdb , /dev/sdc , /dev/sdd , /dev/sde , /dev/sdf , /dev/sdg , /dev/sdh , and then exits.

-s partition

If the partition is not a DOS partition (i.e., the partition id is greater than 10), then the size of that partition is printed on the standard output. This value is normally used as an argument to the mkfs (8) program to specify the size of the partition which will be formatted.

BUGS

Although this man page (written by faith@cs.unc.edu) is poor, there is excellent documentation in the README.fdisk file (written by LeBlanc@mcc.ac.uk) that should always be with the fdisk distribution. If you cannot find this file in the util-linux-* directory or with the fdisk.c source file, then you should write to the distributor of your version of fdisk and complain that you do not have all of the available documentation.

AUTHOR

A. V. Le Blanc (LeBlanc@mcc.ac.uk)
v1.0r: SCSI and extfs support added by Rik Faith (faith@cs.unc.edu)
v1.1r: Bug fixes and enhancements by Rik Faith (faith@cs.unc.edu), with special thanks to Michael Bischoff (i1041905@ws.rz.tu-bs.de or mbi@mo.math.nat.tu-bs.de).
v1.3: Latest enhancements and bug fixes by A. V. Le Blanc, including the addition of the -s option.
v2.0: Disks larger than 2GB are now fully supported, thanks to Remy Card's llseek support.