376 lines
15 KiB
Groff
376 lines
15 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 "February 2016" "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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[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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CHS (Cylinder-Head-Sector) addressing is deprecated and not used by default.
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Please, do not follow old articles and recommendations with "fdisk -S <n> -H
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<n>" advices for SSD or 4K-sector devices.
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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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\fB\-b\fR, \fB\-\-sector\-size\fR \fIsectorsize\fP
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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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\fB\-B\fR, \fB\-\-protect\-boot\fP
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Don't erase the begin of the first disk sector when create a new disk label. This
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feature is supported for GPT and MBR.
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.TP
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\fB\-c\fR, \fB\-\-compatibility\fR[=\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'.
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.TP
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\fB\-h\fR, \fB\-\-help\fR
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Display a help text and exit.
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.TP
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\fB\-L\fR, \fB\-\-color\fR[=\fIwhen\fR]
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Colorize the output. The optional argument \fIwhen\fP
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can be \fBauto\fR, \fBnever\fR or \fBalways\fR. If the \fIwhen\fR argument is omitted,
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it defaults to \fBauto\fR. The colors can be disabled; for the current built-in default
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see the \fB\-\-help\fR output. See also the \fBCOLORS\fR section.
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.TP
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\fB\-l\fR, \fB\-\-list\fR
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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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.BR \-o , " \-\-output " \fIlist\fP
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Specify which output columns to print. Use
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.B \-\-help
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to get a list of all supported columns.
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The default list of columns may be extended if \fIlist\fP is
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specified in the format \fI+list\fP (e.g. \fB-o +UUID\fP).
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.TP
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\fB\-s\fR, \fB\-\-getsz\fR
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Print the size in 512-byte sectors of each given block device. 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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\fB\-t\fR, \fB\-\-type\fR \fItype\fR
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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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.TP
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\fB\-u\fR, \fB\-\-units\fR[=\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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\fB\-C\fR, \fB\-\-cylinders\fR \fInumber\fR
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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.
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.TP
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\fB\-H\fR, \fB\-\-heads\fR \fInumber\fR
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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.
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.TP
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\fB\-S\fR, \fB\-\-sectors\fR \fInumber\fR
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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.) A reasonable value is 63.
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.TP
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\fB\-w\fR, \fB\-\-wipe\fR \fIwhen\fR
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Wipe filesystem, RAID and partition-table signatures from the device, in order
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to avoid possible collisions. The argument \fIwhen\fR can be \fBauto\fR,
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\fBnever\fR or \fBalways\fR. When this option is not given, the default is
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\fBauto\fR, in which case signatures are wiped only when in interactive mode.
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In all cases detected signatures are reported by warning messages
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before a new partition table is created. See also
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.BR wipefs (8)
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command.
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.TP
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\fB\-W\fR, \fB\-\-wipe-partition\fR \fIwhen\fR
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Wipe filesystem, RAID and partition-table signatures from a newly created
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partitions, in order to avoid possible collisions. The argument \fIwhen\fR can
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be \fBauto\fR, \fBnever\fR or \fBalways\fR. When this option is not given, the
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default is \fBauto\fR, in which case signatures are wiped only when in
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interactive mode and after confirmation by user. In all cases detected
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signatures are reported by warning messages before a new partition is
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created. See also
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.BR wipefs (8)
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command.
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.TP
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\fB\-V\fR, \fB\-\-version\fR
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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 SIZES
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The "last sector" dialog accepts partition size specified by number of sectors
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or by +/-<size>{K,B,M,G,...} notation.
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If the size is prefixed by '+' then it is interpreted as relative to the
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partition first sector. If the size is prefixed by '-' then it is interpreted
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as relative to the high limit (last available sector for the partition).
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In the case the size is specified in bytes than the number may be followed by
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the multiplicative suffixes KiB=1024, MiB=1024*1024, and so on for GiB, TiB,
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PiB, EiB, ZiB and YiB. The "iB" is optional, e.g. "K" has the same meaning as
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"KiB".
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The relative sizes are always aligned according to device I/O limits. The
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+/-<size>{K,B,M,G,...} notation is recommended.
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For backward compatibility fdisk also accepts the suffixes KB=1000,
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MB=1000*1000, and so on for GB, TB, PB, EB, ZB and YB. These 10^N suffixes
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are deprecated.
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.SH SCRIPT FILES
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.B fdisk
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allows to read (by 'I' command) sfdisk compatible script files. The script is
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applied to in-memory partition table, and then it is possible to modify the
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partition table before you write it to the device.
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.PP
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And vice-versa it is possible to write the current in-memory disk layout
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to the script file by command 'O'.
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.PP
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The script files are compatible between cfdisk, sfdisk, fdisk and another
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libfdisk applications. For more details see
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.BR sfdisk (8).
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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 by an empty file \fI/etc/terminal-colors.d/fdisk.disable\fR.
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See
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.BR terminal-colors.d (5)
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for more details about colorization configuration. The logical color names
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supported by
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.B fdisk
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are:
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.TP
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.B header
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The header of the output tables.
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.TP
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.B help-title
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The help section titles.
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.TP
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.B warn
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The warning messages.
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.TP
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.B welcome
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The welcome message.
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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 FDISK_DEBUG=all
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enables fdisk debug output.
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.IP LIBFDISK_DEBUG=all
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enables libfdisk debug output.
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.IP LIBBLKID_DEBUG=all
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enables libblkid debug output.
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.IP LIBSMARTCOLS_DEBUG=all
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enables libsmartcols debug output.
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.IP LIBSMARTCOLS_DEBUG_PADDING=on
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use visible padding characters. Requires enabled LIBSMARTCOLS_DEBUG.
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.SH "SEE ALSO"
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.BR cfdisk (8),
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.BR mkfs (8),
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.BR partx (8),
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.BR sfdisk (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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https://www.kernel.org/pub/linux/utils/util-linux/.
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