434 lines
11 KiB
Groff
434 lines
11 KiB
Groff
.\" $FreeBSD$
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.\"
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.Dd October 4, 1996
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.Dt FDISK 8
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.Os
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.Sh NAME
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.Nm fdisk
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.Nd PC partition table maintenance program
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.Sh SYNOPSIS
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.Nm
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.Op Fl BIaistu
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.Op Fl b Ar bootcode
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.Op Fl 1234
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.Op Ar disk
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.Bl -tag -width time
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.Nm
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.Fl f Ar configfile
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.Op Fl itv
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.Op Ar disk
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.Sh PROLOGUE
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In order for the BIOS to boot the kernel,
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certain conventions must be adhered to.
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Sector 0 of the disk must contain boot code,
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a partition table,
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and a magic number.
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BIOS partitions can be used to break the disk up into several pieces.
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The BIOS brings in sector 0 and verifies the magic number. The sector
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0 boot code then searches the partition table to determine which
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partition is marked
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.Em active .
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This boot code then brings in the bootstrap from the
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.Em active
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partition and, if marked bootable, runs it.
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Under DOS,
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you can have one or more partitions with one
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.Em active .
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The DOS
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.Nm
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program can be used to divide space on the disk into partitions and set one
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.Em active .
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.Sh DESCRIPTION
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The
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.Fx
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program
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.Nm
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serves a similar purpose to the DOS program. The first form is used to
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display partition information or to interactively edit the partition
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table. The second is used to write a partition table using a
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.Ar configfile
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and is designed to be used by other scripts/programs.
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.Pp
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Options are:
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.It Fl a
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Change the active partition only. Ignored if
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.Fl f
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is given.
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.It Fl b Ar bootcode
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Get the boot code from the file
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.Ar bootcode .
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Default is
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.Pa /boot/mbr .
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.It Fl B
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Reinitialize the boot code contained in sector 0 of the disk. Ignored
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if
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.Fl f
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is given.
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.It Fl f Ar configfile
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Set partition values using the file
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.Ar configfile .
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The
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.Ar configfile
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always modifies existing partitions, unless
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.Fl i
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is also given, in which case all existing partitions are deleted (marked
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as "unused") before the
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.Ar configfile
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is read. The
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.Ar configfile
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can be "-", in which case
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.Ar stdin
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is read. See
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.Sx CONFIGURATION FILE ,
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below, for file syntax.
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.Pp
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.Em WARNING :
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when
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.Fl f
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is used, you are not asked if you really want to write the partition
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table (as you are in the interactive mode). Use with caution!
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.It Fl i
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Initialize sector 0 of the disk. This implies
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.Fl u ,
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unless
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.Fl f
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is given.
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.It Fl I
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Initialize the contents of sector 0
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with one
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.Fx
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slice covering the entire disk.
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.It Fl s
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Print summary information and exit.
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.It Fl t
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Test mode; do not write partition values. Generally used with the
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.Fl f
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option to see what would be written to the partition table. Implies
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.Fl v .
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.It Fl u
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Is used for updating (editing) sector 0 of the disk. Ignored if
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.Fl f
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is given.
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.It Fl v
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Be verbose. When
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.Fl f
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is used,
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.Nm
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prints out the partition table that is written to the disk.
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.It Fl 1234
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Operate on a single fdisk entry only. Ignored if
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.Fl f
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is given.
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.El
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.Pp
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The final disk name can be provided as a
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.Sq bare
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disk name only, e.g.
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.Ql da0 ,
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or as a full pathname.
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If omitted,
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.Nm
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tries to figure out the default disk device name from the
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mounted root device.
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.Pp
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When called with no arguments, it prints the sector 0 partition table.
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An example follows:
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.Bd -literal
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******* Working on device /dev/ad0 *******
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parameters extracted from in-core disklabel are:
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cylinders=769 heads=15 sectors/track=33 (495 blks/cyl)
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parameters to be used for BIOS calculations are:
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cylinders=769 heads=15 sectors/track=33 (495 blks/cyl)
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Warning: BIOS sector numbering starts with sector 1
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Information from DOS bootblock is:
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The data for partition 1 is:
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sysid 165,(FreeBSD/NetBSD/386BSD)
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start 495, size 380160 (185 Meg), flag 0
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beg: cyl 1/ sector 1/ head 0;
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end: cyl 768/ sector 33/ head 14
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The data for partition 2 is:
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sysid 164,(unknown)
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start 378180, size 2475 (1 Meg), flag 0
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beg: cyl 764/ sector 1/ head 0;
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end: cyl 768/ sector 33/ head 14
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The data for partition 3 is:
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<UNUSED>
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The data for partition 4 is:
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sysid 99,(ISC UNIX, other System V/386, GNU HURD or Mach)
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start 380656, size 224234 (109 Meg), flag 80
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beg: cyl 769/ sector 2/ head 0;
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end: cyl 197/ sector 33/ head 14
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.Ed
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.Pp
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The disk is divided into three partitions that happen to fill the disk.
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The second partition overlaps the end of the first.
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(Used for debugging purposes)
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.Bl -tag -width "cyl, sector and head"
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.It Em "sysid"
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is used to label the partition.
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.Fx
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reserves the
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magic number 165 decimal (A5 in hex).
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.It Em start No and Em size
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fields provide the start address
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and size of a partition in sectors.
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.It Em "flag 80"
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specifies that this is the active partition.
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.It Em cyl , sector No and Em head
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fields are used to specify the beginning address
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and end address for the partition.
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.It Em Note :
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these numbers are calculated using BIOS's understanding of the disk geometry
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and saved in the bootblock.
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.El
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.Pp
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The flags
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.Fl i
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or
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.Fl u
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are used to indicate that the partition data is to be updated, unless the
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.Fl f
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option is used. If the
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.Fl f
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option is not used, the
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.Nm
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program will enter a conversational mode.
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This mode is designed not to change any data unless you explicitly tell it to.
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.Nm Fdisk
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selects defaults for its questions to guarantee the above behavior.
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.Pp
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It displays each partition
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and ask if you want to edit it.
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If you say yes,
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it will step through each field showing the old value
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and asking for a new one.
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When you are done with a partition,
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.Nm
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will display it and ask if it is correct.
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.Nm Fdisk
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will then proceed to the next entry.
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.Pp
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Getting the
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.Em cyl , sector ,
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and
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.Em head
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fields correct is tricky.
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So by default,
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they will be calculated for you;
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you can specify them if you choose.
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.Pp
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After all the partitions are processed,
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you are given the option to change the
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.Em active
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partition.
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Finally,
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when the all the data for the first sector has been accumulated,
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you are asked if you really want to rewrite sector 0.
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Only if you answer yes,
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will the data be written to disk.
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.Pp
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The difference between the
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.Fl u
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flag and
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.Fl i
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flag is that
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the
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.Fl u
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flag just edits the fields as they appear on the disk.
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While the
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.Fl i
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flag is used to "initialize" sector 0;
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it will setup the last BIOS partition to use the whole disk for
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.Fx ;
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and make it active.
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.Sh NOTES
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The automatic calculation of starting cylinder etc. uses
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a set of figures that represent what the BIOS thinks is the
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geometry of the drive.
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These figures are by default taken from the incore disklabel,
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but the program initially gives you an opportunity to change them.
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This allows the user to create a bootblock that can work with drives
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that use geometry translation under the BIOS.
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.Pp
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If you hand craft your disk layout,
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please make sure that the
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.Fx
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partition starts on a cylinder boundary.
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A number of decisions made later may assume this.
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(This might not be necessary later.)
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.Pp
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Editing an existing partition will most likely cause you to
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lose all the data in that partition.
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.Pp
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You should run this program interactively once or twice to see how it
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works. This is completely safe as long as you answer the last question
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in the negative. There are subtleties that the program detects that are
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not fully explained in this manual page.
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.Sh CONFIGURATION FILE
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When the
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.Fl f
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option is given, a disk's partition table can be written using values
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from a
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.Ar configfile .
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The syntax of this file is very simple. Each line is either a comment or
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a specification, and whitespace (except for newlines) are ignored:
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.Bl -tag -width Ds
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.It Xo
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.Ic #
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.Ar comment ...
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.Xc
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Lines beginning with a "#" are comments and are ignored.
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.It Xo
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.Ic g
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.Ar spec1
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.Ar spec2
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.Ar spec3
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.Xc
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Set the BIOS geometry used in partition calculations. There must be
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three values specified, with a letter preceding each number:
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.Bl -tag -width Ds
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.Sm off
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.It Cm c Ar num
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.Sm on
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Set the number of cylinders to
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.Ar num .
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.Sm off
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.It Cm h Ar num
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.Sm on
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Set the number of heads to
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.Ar num .
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.Sm off
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.It Cm s Ar num
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.Sm on
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Set the number of sectors/track to
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.Ar num .
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.El
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.Pp
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These specs can occur in any order, as the leading letter determines
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which value is which; however, all three must be specified.
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.Pp
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This line must occur before any lines that specify partition
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information.
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.Pp
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It is an error if the following is not true:
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.Bd -literal -offset indent
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1 <= number of cylinders
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1 <= number of heads <= 256
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1 <= number of sectors/track < 64
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.Ed
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.Pp
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The number of cylinders should be less than or equal to 1024, but this
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is not enforced, although a warning will be output. Note that bootable
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.Fx
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partitions (the "/" filesystem) must lie completely within the
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first 1024 cylinders; if this is not true, booting may fail.
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Non-bootable partitions do not have this restriction.
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.Pp
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Example (all of these are equivalent), for a disk with 1019 cylinders,
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39 heads, and 63 sectors:
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.Bd -literal -offset indent
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g c1019 h39 s63
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g h39 c1019 s63
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g s63 h39 c1019
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.Ed
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.It Xo
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.Ic p
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.Ar partition
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.Ar type
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.Ar start
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.Ar length
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.Xc
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Set the partition given by
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.Ar partition
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(1-4) to type
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.Ar type ,
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starting at sector
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.Ar start
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for
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.Ar length
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sectors.
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.Pp
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Only those partitions explicitly mentioned by these lines are modified;
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any partition not referenced by a "p" line will not be modified.
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However, if an invalid partition table is present, or the
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.Fl i
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option is specified, all existing partition entries will be cleared
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(marked as unused), and these "p" lines will have to be used to
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explicitly set partition information. If multiple partitions need to be
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set, multiple "p" lines must be specified; one for each partition.
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.Pp
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These partition lines must occur after any geometry specification lines,
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if one is present.
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.Pp
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The
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.Ar type
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is 165 for
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.Fx
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partitions. Specifying a partition type of zero is
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the same as clearing the partition and marking it as unused; however,
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dummy values (such as "0") must still be specified for
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.Ar start
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and
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.Ar length .
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.Pp
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Note: the start offset will be rounded upwards to a head boundary if
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necessary, and the end offset will be rounded downwards to a cylinder
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boundary if necessary.
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.Pp
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Example: to clear partition 4 and mark it as unused:
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.Bd -literal -offset indent
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p 4 0 0 0
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.Ed
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.Pp
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Example: to set partition 1 to a
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.Fx
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partition, starting at sector 1
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for 2503871 sectors (note: these numbers will be rounded upwards and
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downwards to correspond to head and cylinder boundaries):
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.Pp
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.Bd -literal -offset indent
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p 1 165 1 2503871
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.Ed
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.Pp
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.It Xo
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.Ic a
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.Ar partition
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.Xc
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Make
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.Ar partition
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the active partition. Can occur anywhere in the config file, but only
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one must be present.
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.Pp
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Example: to make partition 1 the active partition:
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.Bd -literal -offset indent
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a 1
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.Ed
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.El
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.Sh FILES
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.Bl -tag -width /boot/mbr -compact
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.It Pa /boot/mbr
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The default boot code
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.El
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.Sh SEE ALSO
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.Xr boot0cfg 8 ,
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.Xr disklabel 8
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.Sh BUGS
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The default boot code will not necessarily handle all partition types
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correctly, in particular those introduced since MS-DOS 6.x.
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.Pp
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The entire program should be made more user-friendly.
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.Pp
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Throughout this man page, the term
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.Sq partition
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is used where it should actually be
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.Sq slice ,
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in order to conform with the terms used elsewhere.
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.Pp
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You cannot use this command to completely dedicate a disk to
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.Fx .
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The
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.Xr disklabel 8
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command must be used for this.
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