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fdisk(8) [debian man page]

CFDISK(8)							 GNU fdisk Manual							 CFDISK(8)

NAME
GNU fdisk, lfdisk, gfdisk - manipulate partition tables on a hard drive SYNOPSIS
fdisk [options] [device] DESCRIPTION
fdisk is a disk partition manipulation program, which allows you to create, destroy, resize, move and copy partitions on a hard drive using a menu-driven interface. It is useful for organising the disk space on a new drive, reorganising an old drive, creating space for new oper- ating systems, and copying data to new hard disks. For a list of the supported partition types, see the --list-partition-types option below. It comes in two variants, gfdisk and lfdisk. Lfdisk aims to resemble Linux fdisk 2.12, while gfdisk supports more advanced disk operations, like resizing the filesystem, moving and copying partitions. When starting fdisk, the default is to run gfdisk. OPTIONS
-h, --help displays a help message. -v, --version displays the program's version. -L, --linux-fdisk turns on Linux fdisk compatibility mode. This is the same as running lfdisk. -G, --gnu-fdisk turns off Linux fdisk compatibility mode. -i, --interactive where necessary, prompts for user intervention. -p, --script never prompts for user intervention. -l, --list lists the partition table on the specified device and exits. If there is no device specified, lists the partition tables on all detected devices. -r, --raw-list displays a hex dump of the partition table of the disk, similar to the way Linux fdisk displays the raw data in the partition table. -u, --sector-units use sectors, instead of cylinders for a default unit. -s, --size=DEVICE prints the size of the partition on DEVICE is printed on the standard output. -t, --list-partition-types displays a list of supported partition types and features. The following options are available only to lfdisk. -b, --sector-size=SIZE Specify the sector size of the disk. Valid values are 512, 1024 and 2048. Should be used only on older kernels, which don't guess the correct sector size. -C, --cylinders=CYLINDERS Specify the number of cylinders of the disk. Currently does nothing, it is left for Linux fdisk compatibility. -H, --heads=HEADS Specify the number of heads of the disk. Reasonable values are 255 or 16. -S, --sectors=SECTORS Specify the number of sectors per track. A reasonable value is 63. BUGS
Before editing a BSD disklabel, the partition with the disklabel should already exist on the disk and be detected by the OS. If you have created a BSD-type partition, you need to write the changes to the disk. If fdisk fails to notify the OS about the changes in partition ta- ble, you need to restart your computer. As fdisk tries to guess the device holding the BSD disklabel, it might fail to edit it at all, even if the OS has detected it. In this case you are adviced to simply open the device with fdisk directly. It is possible that it doesn't work on some operating systems. Getting the size of a partition with -s might fail, if fdisk fails to guess the disk device, for the same reasons as with the previous bug. SEE ALSO
mkfs(8), cfdisk(8), parted(8) The fdisk program is fully documented in the info(1) format GNU fdisk User Manual manual. fdisk 18 August, 2006 CFDISK(8)

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FDISK(8)						     Linux Programmer's Manual							  FDISK(8)

NAME
fdisk - Partition table manipulator for Linux SYNOPSIS
fdisk [-u] [-b sectorsize] [-C cyls] [-H heads] [-S sects] device fdisk -l [-u] [device ...] fdisk -s partition ... fdisk -v DESCRIPTION
Hard disks can be divided into one or more logical disks called partitions. This division is described in the partition table found in sector 0 of the disk. In the BSD world one talks about `disk slices' and a `disklabel'. Linux needs at least one partition, namely for its root file system. It can use swap files and/or swap partitions, but the latter are more efficient. So, usually one will want a second Linux partition dedicated as swap partition. On Intel compatible hardware, the BIOS that boots the system can often only access the first 1024 cylinders of the disk. For this reason people with large disks often create a third partition, just a few MB large, typically mounted on /boot, to store the kernel image and a few auxiliary files needed at boot time, so as to make sure that this stuff is accessible to the BIOS. There may be reasons of security, ease of administration and backup, or testing, to use more than the minimum number of partitions. fdisk (in the first form of invocation) is a menu driven program for creation and manipulation of partition tables. It understands DOS type partition tables and BSD or SUN type disklabels. The device is usually one of the following: /dev/hda /dev/hdb /dev/sda /dev/sdb (/dev/hd[a-h] for IDE disks, /dev/sd[a-p] for SCSI disks, /dev/ed[a-d] for ESDI disks, /dev/xd[ab] for XT disks). A device name refers to the entire disk. The partition is a device name followed by a partition number. For example, /dev/hda1 is the first partition on the first IDE hard disk in the system. Disks can have up to 15 partitions. See also /usr/src/linux/Documentation/devices.txt. A BSD/SUN type disklabel can describe 8 partitions, the third of which should be a `whole disk' partition. Do not start a partition that actually uses its first sector (like a swap partition) at cylinder 0, since that will destroy the disklabel. An IRIX/SGI type disklabel can describe 16 partitions, the eleventh of which should be an entire `volume' partition, while the ninth should be labeled `volume header'. The volume header will also cover the partition table, i.e., it starts at block zero and extends by default over five cylinders. The remaining space in the volume header may be used by header directory entries. No partitions may overlap with the volume header. Also do not change its type and make some file system on it, since you will lose the partition table. Use this type of label only when working with Linux on IRIX/SGI machines or IRIX/SGI disks under Linux. A DOS type partition table can describe an unlimited number of partitions. In sector 0 there is room for the description of 4 partitions (called `primary'). One of these may be an extended partition; this is a box holding logical partitions, with descriptors found in a linked list of sectors, each preceding the corresponding logical partitions. The four primary partitions, present or not, get numbers 1-4. Logi- cal partitions start numbering from 5. In a DOS type partition table the starting offset and the size of each partition is stored in two ways: as an absolute number of sectors (given in 32 bits) and as a Cylinders/Heads/Sectors triple (given in 10+8+6 bits). The former is OK - with 512-byte sectors this will work up to 2 TB. The latter has two different problems. First of all, these C/H/S fields can be filled only when the number of heads and the number of sectors per track are known. Secondly, even if we know what these numbers should be, the 24 bits that are available do not suf- fice. DOS uses C/H/S only, Windows uses both, Linux never uses C/H/S. If possible, fdisk will obtain the disk geometry automatically. This is not necessarily the physical disk geometry (indeed, modern disks do not really have anything like a physical geometry, certainly not something that can be described in simplistic Cylinders/Heads/Sectors form), but is the disk geometry that MS-DOS uses for the partition table. Usually all goes well by default, and there are no problems if Linux is the only system on the disk. However, if the disk has to be shared with other operating systems, it is often a good idea to let an fdisk from another operating system make at least one partition. When Linux boots it looks at the partition table, and tries to deduce what (fake) geometry is required for good cooperation with other systems. 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). 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. Par- titions 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. A sync() and a BLKRRPART ioctl() (reread partition table from disk) are performed before exiting when the partition table has been updated. Long ago it used to be necessary to reboot after the use of fdisk. I do not think this is the case anymore - indeed, rebooting too quickly might cause loss of not-yet-written data. Note that both the kernel and the disk hardware may buffer data. 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. For best results, 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
-b sectorsize Specify the sector size of the disk. Valid values are 512, 1024, or 2048. (Recent kernels know the sector size. Use this only on old kernels or to override the kernel's ideas.) -C cyls Specify the number of cylinders of the disk. I have no idea why anybody would want to do so. -H heads Specify the number of heads of the disk. (Not the physical number, of course, but the number used for partition tables.) Reasonable values are 255 and 16. -S sects Specify the number of sectors per track of the disk. (Not the physical number, of course, but the number used for partition tables.) A reasonable value is 63. -l List the partition tables for the specified devices and then exit. If no devices are given, those mentioned in /proc/partitions (if that exists) are used. -u When listing partition tables, give sizes in sectors instead of cylinders. -s partition The size of the partition (in blocks) is printed on the standard output. -v Print version number of fdisk program and exit. BUGS
There are several *fdisk programs around. Each has its problems and strengths. Try them in the order cfdisk, fdisk, sfdisk. (Indeed, cfdisk is a beautiful program that has strict requirements on the partition tables it accepts, and produces high quality partition tables. Use it if you can. fdisk is a buggy program that does fuzzy things - usually it happens to produce reasonable results. Its single advan- tage is that it has some support for BSD disk labels and other non-DOS partition tables. Avoid it if you can. sfdisk is for hackers only - the user interface is terrible, but it is more correct than fdisk and more powerful than both fdisk and cfdisk. Moreover, it can be used noninteractively.) The IRIX/SGI type disklabel is currently not supported by the kernel. Moreover, IRIX/SGI header directories are not fully supported yet. The option `dump partition table to file' is missing. SEE ALSO
cfdisk(8), mkfs(8), parted(8), sfdisk(8) Linux 2.0 11 June 1998 FDISK(8)
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