659 lines
17 KiB
Groff
659 lines
17 KiB
Groff
.\" $NetBSD: fdisk.8,v 1.70 2010/04/07 09:40:58 wiz Exp $
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.\"
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.Dd April 6, 2010
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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 MS-DOS partition maintenance program
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.Sh SYNOPSIS
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.Nm
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.Op Fl aBFfiSuv
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.Bk -words
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.Oo
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.Fl 0 | 1 | 2 | 3 | E Ar number
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.Op Fl s Ar id/start/size Ns Bq Ar /bootmenu
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.Oc
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.Ek
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.Bk -words
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.Op Fl r Ar file | Fl w Ar file
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.Ek
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.Bk -words
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.Op Fl A Ar ptn_alignment Ns Bq Ar /ptn_0_offset
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.Ek
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.Bk -words
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.Op Fl b Ar cylinders/heads/sectors
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.Ek
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.Bk -words
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.Op Fl c Ar bootcode
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.Ek
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.Bk -words
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.Op Fl T Ar disktype
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.Ek
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.Bk -words
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.Op Fl t Ar disktab
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.Ek
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.Bk -words
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.Op Ar device
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.Ek
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.Nm
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.Fl l
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.Sh DESCRIPTION
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The
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.Nm
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program is used to display or update the
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.Em "master boot record"
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or
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.Em MBR
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in the first sector (sector 0)
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of a disk that uses the MBR style of partitioning.
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The following
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.Nx
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ports use this style of disk partitioning:
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amd64, arc, bebox, cobalt, hpcarm, hpcmips, hpcsh, i386, macppc,
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mvmeppc, netwinder, ofppc, and prep.
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.Pp
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The MBR contains bootable code, a partition table,
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an indication of which partition is
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.Sq active ,
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and (optionally, depending on the boot code) a menu
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for selecting a partition to be booted.
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There can be at most 4 partitions defined in sector 0,
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one of which can be an extended
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partition which can be split into any number of sub-partitions.
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.Pp
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The boot code in the MBR is usually invoked by the BIOS or firmware,
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and the MBR passes control to the next stage boot code
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stored in the first sector of the partition to be booted
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(the
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.Em "partition boot record"
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or
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.Em PBR ) .
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.Pp
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After booting,
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.Nx
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does not use the partitioning done by
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.Nm ,
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instead it uses a
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.Nx
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disklabel saved in sector 1 of the
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.Nx
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partition.
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See
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.Xr mbrlabel 8
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for a way of using information from the MBR
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to construct a
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.Nx
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disklabel.
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.Pp
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The standard MBR boot code will only boot the
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.Sq active
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partition.
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However,
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.Nx
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contains additional boot programs which allow the user to
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interactively select which of the partitions to boot.
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The
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.Sq mbr_ext
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code will also boot
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.Nx
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from an extended partition but will not work on old systems that do not
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support LBA reads, the
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.Sq mbr_com0
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and
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.Sq mbr_com0_9600
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will read and write from a serial port.
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At the start the
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.Nm
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program will determine whether the disk sector 0 is valid as a boot sector.
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(This is determined by checking the magic number.)
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If not,
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.Nm
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will initialise the boot code as well as the partition table.
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During this, all four partitions will be marked empty.
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.Pp
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The flags
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.Fl a ,
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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.
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The
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.Nm
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program will enter an interactive 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
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selects defaults for its questions to guarantee that behaviour.
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.Pp
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If partition data is going to be updated and the disk carries GUID Partition
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Tables,
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.Nm
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will remove both primary and backup GPT headers from the disk.
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See
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.Xr gpt 8
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for information on how to manipulate GUID Partition Tables.
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.Pp
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.Nm
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will calculate the correct
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.Em cylinder ,
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.Em head ,
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and
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.Em sector
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values for any partition you edit.
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If you specify
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.Fl v
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you will be asked whether you want to specify them yourself.
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.Pp
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Finally, when all the data for the first sector has been accumulated,
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.Nm
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will ask if you really want to write the new partition table.
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Only if you reply affirmatively to this question will
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.Nm
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write anything to the disk.
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.Pp
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Available options:
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.Pp
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.Bl -tag -width Ds
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.It Fl 0
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Specify partition slot 0 to be printed or updated.
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.It Fl 1
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Specify partition slot 1 to be printed or updated.
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.It Fl 2
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Specify partition slot 2 to be printed or updated.
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.It Fl 3
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Specify partition slot 3 to be printed or updated.
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.It Fl A Ar ptn_alignment Ns Bq Ar /ptn_0_offset
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Specify the alignment for all partitions and optionally the offset for the
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first partition of the disk and of extended partitions.
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If
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.Ar ptn_alignment
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is specified and
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.Ar ptn_0_offset
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is not specified, then the offset is set to the alignment.
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If
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.Fl A
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isn't specified, then the alignment of the first partition is inspected.
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If it ends on a 2048 sector boundary, then the alignment is set to 2048,
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if the start is a power of 2 less than, or equal to 2048 then the offset
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is set to the start sector.
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If the first partition isn't defined then the alignment and offset for disks
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larger than 128GB is set to 2048 (1MB).
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In all other cases the alignment default to a cylinder
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and the offset to a track (both using the BIOS geometry).
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The 1MB alignment is the same as that used by recent windows versions.
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.It Fl a
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Change the active partition.
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In interactive mode this question will be asked after the partitions
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have been processed.
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.It Fl B
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On an i386 or amd64 system, interactively update the boot selector settings.
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(The boot selector permits the user to interactively select the boot
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partition, and thus which operating system is run, at system boot time; see
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.Xr mbr 8
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for more information.)
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.It Fl b Ar cylinders/heads/sectors
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Specify the BIOS geometry parameters for
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.Ar cylinders ,
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.Ar heads ,
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and
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.Ar sectors .
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It is used only in conjunction with the
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.Fl u
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flag.
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If not specified the BIOS geometry will be obtained using sysctl (i386 and
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amd64) or by solving the simultaenous equations from the existing partition
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information.
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If that fails then either the geometry from the disklabel or 63 sectors and
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16 heads is used.
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.It Fl c Ar bootcode
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Specify the filename that
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.Nm
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should read the bootcode from.
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If the name of a directory is specified, then
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.Nm
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will look for files with the default names in that directory.
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The default is to read from
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.Pa /usr/mdec/mbr ,
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.Pa /usr/mdec/mbr_bootsel
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or
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.Pa /usr/mdec/mbr_ext
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depending on whether
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.Ar bootmenu
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was specified for any partitions
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on an i386 machine, and leave the bootcode empty for other
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machines.
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.It Fl E Ar number
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Specify extended partition
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.Ar number
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to be printed or updated.
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If the specified extended partition doesn't exist on updating partition data
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an additional extended partition will be created.
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.It Fl F
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Indicate that
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.Ar device
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is a regular file.
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Unless the geometry of
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.Ar device
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is told to
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.Nm
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by
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.Fl T Ar disktype ,
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.Nm
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will count the 512-byte sectors in
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.Ar device
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and produce a fake geometry.
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If
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.Ar device
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is a regular file,
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.Fl F
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will be used implicitly.
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.It Fl f
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Run
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.Nm
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in a non-interactive mode.
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In this mode, you can only change the disk parameters by using the
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.Fl b
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flag.
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This is provided only so scripts or other programs may use
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.Nm
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as part of an automatic installation process.
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.Pp
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Using the
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.Fl f
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flag with
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.Fl u
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makes it impossible to specify the starting and ending
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.Ar cylinder ,
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.Ar head ,
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and
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.Ar sector
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fields
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.Pq only Ar start No and Ar size No can be specified by Fl s No option .
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They will be automatically computed using the BIOS geometry.
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.It Fl i
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Explicitly request initialisation of the master boot code
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(similar to what
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.Ic fdisk /mbr
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does under
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.Tn MS-DOS ) ,
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even if the magic number in the first sector is ok.
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The partition table is left alone by this (but see above).
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.It Fl l
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Lists known
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.Em sysid
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values and exit.
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.It Fl r Ar file
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Read the boot record from file
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.Ar file
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instead of the specified disk.
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The geometry information used is still that of the disk volume.
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Any changes are written back to the file.
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.It Fl S
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When used with no other flags print a series of
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.Pa /bin/sh
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commands for setting variables to the partition information.
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This could be used by installation scripts.
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.It Fl s Ar id/start/size Ns Bq Ar /bootmenu
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Specify the partition
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.Ar id ,
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.Ar start ,
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.Ar size ,
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and optionally
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.Ar bootmenu .
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This flag requires the use of a partition selection flag
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.Pq Fl 0 , 1 , 2 , 3 , No or Fl E Ar number .
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.It Fl T Ar disktype
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Use the disklabel
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.Ar disktype
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instead of the disklabel on
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.Ar device .
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.It Fl t Ar disktab
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Read
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.Ar disktype
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from the named
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.Xr disktab 5
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file instead of from
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.Pa /etc/disktab .
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.It Fl u
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Update partition data, including
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.Em id , start , No and Em size .
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Unless
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.Fl f
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option
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.Pq non-interactive mode
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is specified,
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.Nm
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will display the partitions and interactively ask which one you want to edit.
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.Nm
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will step through each field showing the old value and asking for a new one.
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The
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.Em start
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and
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.Em size
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can be specified in blocks (NN),
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cylinders (NNc or NNcyl),
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megabytes (NNm or NNMB),
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or gigabytes (NNg or NNGB), values in megabytes and gigabytes
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will be rounded to the nearest cylinder boundary.
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The
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.Em size
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may be specified as
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.Em $
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in which case the partition will extend to the end of the available free space.
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.Pp
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In a non-interactive mode
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.Pq specified by Fl f No option ,
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partition data should be specified by
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.Fl s
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option.
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A partition selection option
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.Pq Fl 0 , 1 , 2 , 3 , No or Fl E Ar number
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should also be specified to select a partition slot to be updated.
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.Pp
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.Nm
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will not allow you to create partitions which overlap.
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If
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.Fl u
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and
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.Fl s
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are specified in a non-interactive mode
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then the details of the specified partition will be changed.
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Any other partitions which overlap the requested part of the disk will be
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silently deleted.
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.Pp
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If
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.Em bootmenu
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is specified for any partition
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.Nm
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will determine whether the installed boot code supports the bootselect code,
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if it doesn't you will be asked whether you want to install the required
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boot code.
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To remove a
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.Em bootmenu
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label, simply press
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.Aq space
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followed by
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.Aq return .
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.It Fl v
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Be more verbose, specifying
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.Fl v
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more than once may increase the amount of output.
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.Pp
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Using
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.Fl v
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with
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.Fl u
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allows the user to change more parameters than normally permitted.
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.It Fl w Ar file
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Write the modified partition table to file
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.Ar file
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instead of the disk.
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.El
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.Pp
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When called with no arguments, it prints the partition table.
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An example follows:
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.Bd -literal
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Disk: /dev/rwd0d
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NetBSD disklabel disk geometry:
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cylinders: 16383, heads: 16, sectors/track: 63 (1008 sectors/cylinder)
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total sectors: 40032696
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BIOS disk geometry:
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cylinders: 1023, heads: 255, sectors/track: 63 (16065 sectors/cylinder)
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total sectors: 40032696
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Partition table:
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0: NetBSD (sysid 169)
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bootmenu: net 1.5.
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start 4209030, size 8289540 (4048 MB, Cyls 262-778), Active
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1: Primary DOS with 32 bit FAT (sysid 11)
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bootmenu: win98
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start 63, size 4208967 (2055 MB, Cyls 0-262)
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2: NetBSD (sysid 169)
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bootmenu: current
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start 32515560, size 7517136 (3670 MB, Cyls 2024-2491/234/40)
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3: Ext. partition - LBA (sysid 15)
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start 12498570, size 20016990 (9774 MB, Cyls 778-2024)
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Extended partition table:
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E0: NetBSD (sysid 169)
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bootmenu: test
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start 12498633, size 12305727 (6009 MB, Cyls 778-1544)
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E1: Primary DOS with 32 bit FAT (sysid 11)
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start 24804423, size 4096512 (2000 MB, Cyls 1544-1799)
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E2: Primary DOS with 32 bit FAT (sysid 11)
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start 28900998, size 3614562 (1765 MB, Cyls 1799-2024)
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Bootselector enabled, infinite timeout.
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First active partition: 0
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.Ed
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.Pp
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This example disk is divided into four partitions, the last of which is
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an extended partition.
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The sub-partitions of the extended partition are also shown.
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In this case there is no free space in either the disk or in the extended
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partition.
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.Pp
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The various fields in each partition entry are:
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.br
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.in +4
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.Em ptn_number : id_name
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(sysid
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.Em id_number )
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.br
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.in +4
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bootmenu:
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.Em bootmenu
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.br
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start
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.Em start ,
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size
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.Em size ( MB
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MB, Cyls
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.Em first Ns No - Ns Em next )
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.Op , Active
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.in -4
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.in -4
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.Bl -tag -width "bootmenu"
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.It Em ptn_number
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is the number of the partition.
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.It Em id_name
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is the name of the filesystem type or operating system that uses this partition.
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.It Em id_number
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is the number that identifies the partition type.
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169 decimal is used for
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.Nx
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partitions,
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15 decimal to create an extended partition
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and 0 to mark a partition as unused.
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Use
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.Nm
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.Fl l
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to list the known partition types.
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.It Em bootmenu
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is the menu prompt output by the interactive boot code for this partition.
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This line is omitted if the prompt is not defined.
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.It Em start , Em size
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are the start address and size of the partition in sectors.
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.It Em MB
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is the size of the partition in megabytes.
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.It Em first , Em next
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are the bounds of this partition displayed as cylinder/head/sector.
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If the partition starts (or ends) on a cylinder boundary the head and
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sector values are omitted.
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If
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.Fl v
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is not specified the start of extended partitions and the first partition
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on the disk are rounded down to include the mandatory red tape in the
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preceding track.
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.It Active
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is output if this is the active partition.
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.El
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.Pp
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If the
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.Fl v
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flag is specified, the beginning and end of each partition are also
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displayed as follows:
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.in +4
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beg: cylinder
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.Em cylinder ,
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head
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.Em head ,
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sector
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.Em sector
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.br
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end: cylinder
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.Em cylinder ,
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head
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.Em head ,
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sector
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.Em sector
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.in -4
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.Bl -tag -width "bootmenu"
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.It Em "cylinder" , Em "head" , Em "sector"
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are the beginning or ending address of a partition.
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.Pp
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.Em "Note:"
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these numbers are read from the bootblock, so are the values calculated
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by a previous run of
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.Nm .
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.El
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.Pp
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.Nm
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attempts to check whether each partition is bootable,
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by checking the magic number and some other characteristics
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of the first sector of each partition (the PBR).
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If the partition does not appear to be bootable,
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.Nm
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will print a line containing
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.Dq "PBR is not bootable"
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followed by an error message.
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If the partition is bootable, and if the
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.Fl v
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flag is specified,
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.Nm
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will print
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.Dq "PBR appears to be bootable" .
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If the
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.Fl v
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flag is specified more than once,
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.Nm
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will print the heading
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.Dq "Information from PBR:"
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followed by one or more lines of information gleaned from the PBR;
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this additional information may be incorrect or misleading,
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because different operating systems use different PBR formats.
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Note that, even if no errors are reported, an attempt to boot
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from the partition might fail.
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.Nx
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partitions may be made bootable using
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.Xr installboot 8 .
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.Sh NOTES
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This program is only available (and useful) on systems with PC-platform-style
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MBR partitioning.
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.Pp
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Traditionally the partition boundaries should be on cylinder boundaries
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using the BIOS geometry, with the exception of the first partition,
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which traditionally begins in the second track of the first cylinder
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|
(cylinder 0, head 1, sector 1).
|
|
Although the BIOS geometry is typically different from the geometry
|
|
reported by the drive, neither will match the actual physical geometry
|
|
for modern disks (the actual geometry will vary across the disk).
|
|
Keeping the partition boundaries on cylinder boundaries makes partitioning
|
|
a driver easier as only relatively small numbers need be entered.
|
|
.Pp
|
|
The automatic calculation of the starting cylinder and
|
|
other parameters uses
|
|
a set of figures that represent what the BIOS thinks is the
|
|
geometry of the drive.
|
|
The default values should be correct for the system on which
|
|
.Nm
|
|
is run; however, if you move the disk to a different system, the
|
|
BIOS of that system might use a different geometry translation.
|
|
.Pp
|
|
If you run the equivalent of
|
|
.Nm
|
|
on a different operating system then the
|
|
.Ar bootmenu
|
|
strings associated with extended partitions may be lost.
|
|
.Pp
|
|
Editing an existing partition is risky, and may cause you to
|
|
lose all the data in that partition.
|
|
.Pp
|
|
You should run this program interactively once or twice to see how it works.
|
|
This is completely safe as long as you answer the last question in the negative.
|
|
You can also specify
|
|
.Fl w Ar file
|
|
to write the output to a file and later specify
|
|
.Fl r Ar file
|
|
to read back the updated information.
|
|
This can be done without having write access to the disk volume.
|
|
.Sh FILES
|
|
.Bl -tag -width /usr/mdec/mbrxxxxxxxx -compact
|
|
.It Pa /usr/mdec/mbr
|
|
Default location of i386 bootcode
|
|
.It Pa /usr/mdec/mbr_bootsel
|
|
Default location of i386 bootselect code
|
|
.It Pa /usr/mdec/mbr_ext
|
|
Default location of i386 bootselect for extended partitions
|
|
.El
|
|
.Sh EXAMPLES
|
|
Update MBR partition data of
|
|
.Pa /dev/rwd0d
|
|
in interactive mode:
|
|
.Pp
|
|
.Dl Ic fdisk -u /dev/rwd0d
|
|
.Pp
|
|
Change active MBR partition of
|
|
.Pa /dev/rwd0d
|
|
in interactive mode:
|
|
.Pp
|
|
.Dl Ic fdisk -a /dev/rwd0d
|
|
.Pp
|
|
Install MBR bootcode
|
|
.Pa /usr/mdec/mbr_bootsel
|
|
into
|
|
.Pa /dev/rwd0d :
|
|
.Pp
|
|
.Dl Ic fdisk -c /usr/mdec/mbr_bootsel /dev/rwd0d
|
|
.Pp
|
|
Set MBR partition data for slot 0 of
|
|
.Pa /dev/rwd0d
|
|
specifying values without prompt:
|
|
.Pp
|
|
.Dl Ic fdisk -f -u -0 -s 169/63/2097089 /dev/rwd0d
|
|
.Pp
|
|
Make partition slot 0 of
|
|
.Pa /dev/rwd0d
|
|
active without prompt:
|
|
.Pp
|
|
.Dl Ic fdisk -f -a -0 /dev/rwd0d
|
|
.Pp
|
|
Initialize and create MBR partition data using bootcode
|
|
.Pa destdir/usr/mdec/mbr
|
|
without prompt against 1GB disk image file
|
|
.Pa diskimg :
|
|
.Pp
|
|
.Dl Ic fdisk -f -i -b 130/255/63 -c destdir/usr/mdec/mbr -F diskimg
|
|
.Pp
|
|
Create MBR partition data for slot 0 which has an active NetBSD partition
|
|
using whole disk without prompt against 1GB disk image file
|
|
.Pa diskimg :
|
|
.Pp
|
|
.Dl Ic fdisk -f -a -u -0 -s 169/63/2097089 -F diskimg
|
|
.Sh SEE ALSO
|
|
.Xr disktab 5 ,
|
|
.Xr boot 8 ,
|
|
.Xr disklabel 8 ,
|
|
.Xr gpt 8 ,
|
|
.Xr installboot 8 ,
|
|
.Xr mbr 8 ,
|
|
.Xr mbrlabel 8
|
|
.Sh BUGS
|
|
The word
|
|
.Sq partition
|
|
is used to mean both an MBR partition and a
|
|
.Nx
|
|
partition, sometimes in the same sentence.
|
|
.Pp
|
|
There are subtleties that the program detects that are not explained in
|
|
this manual page.
|