464 lines
10 KiB
Groff
464 lines
10 KiB
Groff
.\" $FreeBSD$
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.\"
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.Dd April 30, 2007
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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 slice table maintenance utility
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.Sh SYNOPSIS
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.Nm
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.Op Fl BIaipstu
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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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.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 slice table,
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and a magic number.
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BIOS slices 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.
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The sector
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0 boot code then searches the slice table to determine which
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slice is marked
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.Dq active .
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This boot code then brings in the bootstrap from the
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active slice and, if marked bootable, runs it.
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Under
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.Tn DOS ,
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you can have one or more slices with one active.
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The
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.Tn DOS
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.Nm
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utility can be used to divide space on the disk into slices and set one
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active.
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.Sh DESCRIPTION
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The
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.Fx
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utility,
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.Nm ,
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serves a similar purpose to the
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.Tn DOS
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utility.
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The first form is used to
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display slice information or to interactively edit the slice
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table.
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The second is used to write a slice 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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.Bl -tag -width indent
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.It Fl a
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Change the active slice only.
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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.
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Ignored 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 slice 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 slices, unless
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.Fl i
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is also given, in which case all existing slices are deleted (marked
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as
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.Dq unused )
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before the
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.Ar configfile
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is read.
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The
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.Ar configfile
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can be
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.Sq Fl ,
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in which case standard input is read.
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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 slices
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table (as you are in the interactive mode).
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Use with caution!
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.It Fl i
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Initialize sector 0 of the disk.
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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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for one
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.Fx
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slice covering the entire disk.
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.It Fl p
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Print a slice table in
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.Nm
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configuration file format and exit; see
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.Sx CONFIGURATION FILE ,
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below.
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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 slice values.
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Generally used with the
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.Fl f
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option to see what would be written to the slice table.
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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.
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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.
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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 slice table that is written to the disk.
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.It Fl 1234
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Operate on a single slice table entry only.
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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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.Dq bare
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disk name only, e.g.\&
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.Pa 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 slice 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 slices that happen to fill the disk.
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The second slice overlaps the end of the first.
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(Used for debugging purposes.)
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.Bl -tag -width ".Em cyl , sector No and Em head"
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.It Em sysid
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is used to label the slice.
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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 Xo
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.Em start
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and
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.Em size
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.Xc
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fields provide the start address
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and size of a slice in sectors.
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.It Em "flag 80"
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specifies that this is the active slice.
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.It Xo
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.Em cyl , sector
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and
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.Em head
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.Xc
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fields are used to specify the beginning and end addresses of the slice.
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.El
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.Pp
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.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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.Pp
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The
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.Fl i
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and
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.Fl u
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flags are used to indicate that the slice data is to be updated.
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Unless the
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.Fl f
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option is also given,
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.Nm
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will enter a conversational mode.
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In this mode, no changes will be written to disk unless you explicitly tell
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.Nm
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to.
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.Pp
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The
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.Nm
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utility will display each slice and ask whether you want to edit it.
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If you say yes,
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.Nm
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will step through each field, show you the old value,
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and ask you for a new one.
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When you are done with the slice,
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.Nm
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will display it and ask you whether it is correct.
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It 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, so by default,
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they will be calculated for you;
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you can specify them if you choose to though.
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.Pp
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After all the slices are processed,
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you are given the option to change the
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.Dq active
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slice.
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Finally, when all the new data for sector 0 has been accumulated,
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you are asked to confirm whether you really want to rewrite it.
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.Pp
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The difference between the
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.Fl u
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and
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.Fl i
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flags is that
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the
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.Fl u
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flag just edits (updates) 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
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.Dq initialize
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sector 0;
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it will set up the last BIOS slice 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 the
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geometry of the drive is.
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These figures are taken from the in-core disklabel by default,
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but
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.Nm
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initially gives you an opportunity to change them.
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This allows you 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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slice 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 slice will most likely result in the loss of
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all data in that slice.
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.Pp
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You should run
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.Nm
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interactively once or twice to see how it works.
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This is completely safe as long as you answer the last question
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in the negative.
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There are subtleties that
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.Nm
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detects that are 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 slice 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;
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each line is either a comment or a specification, as follows:
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.Bl -tag -width indent
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.It Ic # Ar comment ...
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Lines beginning with a
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.Ic #
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are comments and are ignored.
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.It Ic g Ar spec1 spec2 spec3
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Set the BIOS geometry used in slice calculations.
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There must be
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three values specified, with a letter preceding each number:
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.Bl -tag -width indent
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.It Cm c Ns Ar num
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Set the number of cylinders to
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.Ar num .
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.It Cm h Ns Ar num
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Set the number of heads to
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.Ar num .
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.It Cm s Ns Ar num
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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 slice
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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 printed.
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Note that bootable
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.Fx
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slices (the
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.Dq Pa /
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file system) 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 slices 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 Ic p Ar slice type start length
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Set the slice given by
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.Ar slice
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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 slices explicitly mentioned by these lines are modified;
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any slice not referenced by a
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.Ic p
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line will not be modified.
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However, if an invalid slice table is present, or the
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.Fl i
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option is specified, all existing slice entries will be cleared
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(marked as unused), and these
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.Ic p
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lines will have to be used to
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explicitly set slice information.
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If multiple slices need to be
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set, multiple
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.Ic p
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lines must be specified; one for each slice.
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.Pp
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These slice 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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slices.
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Specifying a slice type of zero is
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the same as clearing the slice and marking it as unused; however,
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dummy values (such as
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.Dq 0 )
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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 slice 4 and mark it as unused:
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.Pp
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.Dl "p 4 0 0 0"
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.Pp
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Example: to set slice 1 to a
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.Fx
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slice, 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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.Dl "p 1 165 1 2503871"
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.Pp
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.It Ic a Ar slice
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Make
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.Ar slice
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the active slice.
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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 slice 1 the active slice:
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.Pp
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.Dl "a 1"
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.El
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.Sh FILES
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.Bl -tag -width ".Pa /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 bsdlabel 8 ,
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.Xr newfs 8
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.Sh BUGS
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The default boot code will not necessarily handle all slice types
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correctly, in particular those introduced since
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.Tn MS-DOS
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6.x.
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.Pp
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The entire utility should be made more user-friendly.
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.Pp
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Most users new to
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.Fx
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do not understand the difference between
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.Dq slice
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and
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.Dq partition ,
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causing difficulty to adjust.
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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 bsdlabel 8
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command must be used for this.
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