283 lines
11 KiB
Groff
283 lines
11 KiB
Groff
.\" Copyright 1992, 1993 Rickard E. Faith (faith@cs.unc.edu)
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.\" Copyright 1998 Andries E. Brouwer (aeb@cwi.nl)
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.\" Copyright 2012 Davidlohr Bueso <dave@gnu.org>
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.\" Copyright (C) 2013 Karel Zak <kzak@redhat.com>
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.\" May be distributed under the GNU General Public License
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.TH FDISK 8 "September 2013" "util-linux" "System Administration"
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.SH NAME
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fdisk \- manipulate disk partition table
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.SH SYNOPSIS
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.B fdisk
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.RB [ options ]
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.I device
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.sp
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.B fdisk \-l
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.RI [ device ...]
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.SH DESCRIPTION
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.B fdisk
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is a dialog-driven program for creation and manipulation of partition tables.
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It understands GPT, MBR, Sun, SGI and BSD partition tables.
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Block devices can be divided into one or more logical disks called
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.IR partitions .
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This division is recorded in the
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.IR "partition table" ,
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usually found in sector 0 of the disk.
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(In the BSD world one talks about `disk slices' and a `disklabel'.)
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All partitioning is driven by device I/O limits (the topology) by default.
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.B fdisk
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is able to optimize the disk layout for a 4K-sector size and use an alignment offset on
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modern devices for MBR and GPT. It is always a good idea to follow \fBfdisk\fR's defaults
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as the default values (e.g. first and last partition sectors) and partition
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sizes specified by the +<size>{M,G,...} notation are always aligned according
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to the device properties.
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Note that
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.BR partx (8)
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provides a rich interface for scripts to print disk layouts,
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.B fdisk
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is mostly designed for humans. Backward compatibility in the output of
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.B fdisk
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is not guaranteed. The input (the commands) should always be backward compatible.
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.SH OPTIONS
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.TP
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.BI "\-b " sectorsize
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Specify the sector size of the disk. Valid values are 512, 1024, 2048, and 4096.
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(Recent kernels know the sector size. Use this option only on old kernels or
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to override the kernel's ideas.) Since util-linux-2.17, \fBfdisk\fR differentiates
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between logical and physical sector size. This option changes both sector sizes to
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.IB sectorsize .
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.TP
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.BR "\-c"[=\fImode\fR]
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Specify the compatibility mode, 'dos' or 'nondos'. The default is non-DOS
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mode. For backward compatibility, it is possible to use the option without
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the \fImode\fR argument -- then the default is used. Note that the optional
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\fImode\fR argument cannot be separated from the \fB-c\fR option by a space,
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the correct form is for example '-c=dos'. This option is DEPRECATED.
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.TP
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.BI "\-C " cylinders
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Specify the number of cylinders of the disk.
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I have no idea why anybody would want to do so. This option is DEPRECATED.
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.TP
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.BI "\-H " heads
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Specify the number of heads of the disk. (Not the physical number,
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of course, but the number used for partition tables.)
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Reasonable values are 255 and 16. This option is DEPRECATED.
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.TP
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.BI "\-S " sectors
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Specify the number of sectors per track of the disk.
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(Not the physical number, of course, but the number used for
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partition tables.)
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A reasonable value is 63. This option is DEPRECATED.
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.TP
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.BI \-h
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Display a help text and exit.
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.TP
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.BR "\-L"[=\fIwhen\fR]
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Colorize the output in interactive mode. The optional argument \fIwhen\fP can
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be \fBauto\fR, \fBnever\fR or \fBalways\fR. The default is \fBauto\fR.
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.TP
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.B \-l
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List the partition tables for the specified devices and then exit.
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If no devices are given, those mentioned in
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.I /proc/partitions
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(if that file exists) are used.
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.TP
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.BI "\-s " partition...
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Print the size (in blocks) of each given partition. This option is DEPRECATED
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in favour of
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.BR blockdev (1).
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.TP
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.BI "\-t " type
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Enable support only for disklabels of the specified \fItype\fP, and disable
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support for all other types.
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This is necessary for example to access a protective or hybrid MBR on devices
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with GPT.
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.TP
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.BR "\-u"[=\fIunit\fR]
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When listing partition tables, show sizes in 'sectors' or in 'cylinders'. The
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default is to show sizes in sectors. For backward compatibility, it is possible
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to use the option without the \fIunit\fR argument -- then the default is used.
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Note that the optional \fIunit\fR argument cannot be separated from the \fB-u\fR
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option by a space, the correct form is for example '-u=cylinders'.
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.TP
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.B \-v
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Display version information and exit.
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.SH DEVICES
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The
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.I device
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is usually /dev/sda, /dev/sdb or so. A device name refers to the entire disk.
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Old systems without libata (a library used inside the Linux kernel to support
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ATA host controllers and devices) make a difference between IDE and SCSI disks.
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In such cases the device name will be /dev/hd* (IDE) or /dev/sd* (SCSI).
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The
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.I partition
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is a device name followed by a partition number. For example, /dev/sda1 is the
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first partition on the first hard disk in the system. See also Linux kernel
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documentation (the Documentation/devices.txt file).
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.SH DISK LABELS
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.B GPT (GUID Partition Table)
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.RS
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GPT is modern standard for the layout of the partition table. GPT uses 64-bit
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logical block addresses, checksums, UUIDs and names for partitions and an
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unlimited number of partitions (although the number of partitions is
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usually restricted to 128 in many partitioning tools).
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Note that the first sector is still reserved for a
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.B protective MBR
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in the GPT specification. It prevents MBR-only partitioning tools
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from mis-recognizing and overwriting GPT disks.
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GPT is always a better choice than MBR, especially on modern hardware with a UEFI
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boot loader.
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.RE
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.B DOS-type (MBR)
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.RS
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A DOS-type partition table can describe an unlimited number of partitions. In sector 0
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there is room for the description of 4 partitions (called `primary'). One of
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these may be an extended partition; this is a box holding logical partitions,
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with descriptors found in a linked list of sectors, each preceding the
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corresponding logical partitions. The four primary partitions, present or not,
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get numbers 1-4. Logical partitions are numbered starting from 5.
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In a DOS-type partition table the starting offset and the size of each
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partition is stored in two ways: as an absolute number of sectors (given in 32
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bits), and as a
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.B Cylinders/Heads/Sectors
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triple (given in 10+8+6 bits). The former is OK -- with 512-byte sectors this
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will work up to 2 TB. The latter has two problems. First, these C/H/S fields
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can be filled only when the number of heads and the number of sectors per track
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are known. And second, even if we know what these numbers should be, the 24
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bits that are available do not suffice. DOS uses C/H/S only, Windows uses
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both, Linux never uses C/H/S. The
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.B C/H/S addressing is deprecated
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and may be unsupported in some later fdisk version.
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.B Please, read the DOS-mode section if you want DOS-compatible partitions.
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.B fdisk
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does not care about cylinder boundaries by default.
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.RE
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.B BSD/Sun-type
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.RS
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A BSD/Sun disklabel can describe 8 partitions, the third of which should be a `whole
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disk' partition. Do not start a partition that actually uses its first sector
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(like a swap partition) at cylinder 0, since that will destroy the disklabel.
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Note that a
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.B BSD label
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is usually nested within a DOS partition.
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.RE
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.B IRIX/SGI-type
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.RS
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An IRIX/SGI disklabel can describe 16 partitions, the eleventh of which should be an entire
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`volume' partition, while the ninth should be labeled `volume header'. The
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volume header will also cover the partition table, i.e., it starts at block
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zero and extends by default over five cylinders. The remaining space in the
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volume header may be used by header directory entries. No partitions may
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overlap with the volume header. Also do not change its type or make some
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filesystem on it, since you will lose the partition table. Use this type of
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label only when working with Linux on IRIX/SGI machines or IRIX/SGI disks under
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Linux.
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.RE
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A sync() and an ioctl(BLKRRPART) (rereading the partition table from disk)
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are performed before exiting when the partition table has been updated.
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.SH "DOS mode and DOS 6.x WARNING"
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.B Note that all this is deprecated. You don't have to care about things like
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.B geometry and cylinders on modern operating systems. If you really want
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.B DOS-compatible partitioning then you have to enable DOS mode and cylinder
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.B units by using the '-c=dos -u=cylinders' fdisk command-line options.
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The DOS 6.x FORMAT command looks for some information in the first sector of
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the data area of the partition, and treats this information as more reliable
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than the information in the partition table. DOS FORMAT expects DOS FDISK to
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clear the first 512 bytes of the data area of a partition whenever a size
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change occurs. DOS FORMAT will look at this extra information even if the /U
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flag is given -- we consider this a bug in DOS FORMAT and DOS FDISK.
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The bottom line is that if you use \fBfdisk\fR or \fBcfdisk\fR to change the
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size of a DOS partition table entry, then you must also use
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.BR dd "(1) to " "zero the first 512 bytes"
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of that partition before using DOS FORMAT to format the partition. For
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example, if you were using \fBfdisk\fR to make a DOS partition table entry for
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/dev/sda1, then (after exiting \fBfdisk\fR and rebooting Linux so that the
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partition table information is valid) you would use the command "dd
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if=/dev/zero of=/dev/sda1 bs=512 count=1" to zero the first 512 bytes of the
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partition.
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.B fdisk
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usually obtains the disk geometry automatically. This is not necessarily the
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physical disk geometry (indeed, modern disks do not really have anything like a
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physical geometry, certainly not something that can be described in the simplistic
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Cylinders/Heads/Sectors form), but it is the disk geometry that MS-DOS uses for
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the partition table.
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Usually all goes well by default, and there are no problems if Linux is the
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only system on the disk. However, if the disk has to be shared with other
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operating systems, it is often a good idea to let an fdisk from another
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operating system make at least one partition. When Linux boots it looks at the
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partition table, and tries to deduce what (fake) geometry is required for good
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cooperation with other systems.
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Whenever a partition table is printed out in DOS mode, a consistency check is
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performed on the partition table entries. This check verifies that the
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physical and logical start and end points are identical, and that each
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partition starts and ends on a cylinder boundary (except for the first
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partition).
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Some versions of MS-DOS create a first partition which does not begin
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on a cylinder boundary, but on sector 2 of the first cylinder.
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Partitions beginning in cylinder 1 cannot begin on a cylinder boundary, but
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this is unlikely to cause difficulty unless you have OS/2 on your machine.
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For best results, you should always use an OS-specific partition table
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program. For example, you should make DOS partitions with the DOS FDISK
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program and Linux partitions with the Linux fdisk or Linux cfdisk programs.
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.SH COLORS
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Implicit coloring can be disabled as follows:
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.RS
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.br
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.BI "touch /etc/terminal-colors.d/fdisk.disable"
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.br
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.RE
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For more details see
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.BR terminal-colors.d (5).
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.SH AUTHORS
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.MT kzak@redhat.com
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Karel Zak
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.ME
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.br
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.MT dave@gnu.org
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Davidlohr Bueso
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.ME
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.br
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.PP
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The original version was written by
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Andries E. Brouwer, A. V. Le Blanc and others.
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.SH ENVIRONMENT
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.IP "Setting LIBFDISK_DEBUG=0xffff enables debug output."
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.SH "SEE ALSO"
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.BR cfdisk (8),
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.BR sfdisk (8),
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.BR mkfs (8),
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.BR partx (8)
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.SH AVAILABILITY
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The fdisk command is part of the util-linux package and is available from
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ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
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