457 lines
11 KiB
Groff
457 lines
11 KiB
Groff
.\" $NetBSD: fdisk.8,v 1.43 2003/10/06 12:02:52 lukem Exp $
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.\"
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.Dd October 6, 2003
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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 afiuvBS
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.Bk -words
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.Op Fl 0 | 1 | 2 | 3
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.Ek
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.Bk -words
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.Op Fl E Ar number
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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 s Ar id/start/size Ns Bq Ar /bootmenu
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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 r|w Ar file
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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 divide space on a disk into partitions and set
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one active.
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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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.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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.Pp
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The standard MBR boot code will only boot the 'active' partition.
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However
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.Nx
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contains two alternate boot programs which allow the user to
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interactively select which of the partitions to boot.
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The 'mbr_ext' code will 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.
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.Pp
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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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.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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Update partition slot 0.
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.It Fl 1
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Update partition slot 1.
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.It Fl 2
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Update partition slot 2.
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.It Fl 3
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Update partition slot 3.
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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 Ar cylinders/heads/sectors
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Specify the BIOS 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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.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.
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See
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.Xr mbr 8
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for more information.)
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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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Update extended partition
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.Ar number .
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If the specified extended partition doesn't exist an additional extended
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partition will be created.
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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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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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They will be automatically computed using the BIOS geometry.
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.br
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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 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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.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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.Nm 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 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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.Po
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.Fl 0 ,
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.Fl 1 ,
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.Fl 2 ,
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.Fl 3 ,
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or
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.Fl E Ar number
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.Pc
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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 u
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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), cylinders (nnc) or megabytes (nnm), values
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in megabytes 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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.br
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.Nm
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will not allow you to create partitions which overlap.
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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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.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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.br
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Specifying
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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 explicitly specify some values for with the default
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ies usually correct.
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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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.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 Xo
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.Em start ,
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.Em size
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.Xc
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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 Xo
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.Em first ,
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.Em next
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.Xc
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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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preceeding 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 given two additional lines are output for each partition:
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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 Xo
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.Em "cylinder" ,
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.Em "head" ,
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.Em "sector"
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.Xc
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are the beginning or ending address of a partition.
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.br
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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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.Sh NOTES
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Traditionally the partition boundaries should be on cylinder boundaries
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using the BIOS geometry, all of the first track should be reserved
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for use by the BIOS.
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Although the BIOS geometry is typically different from the geometry
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reported by the drive, neither will match the actual physical geometry
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for modern disks (the actual geometry will vary across the disk).
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Keeping the partition boundaries on cylinder boundaries makes partitioning
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a driver easier as only relatively small numbers need be entered.
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.Pp
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The automatic calculation of the starting cylinder and
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other parameters 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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The default values should be correct for the system on which
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.Nm
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is run, however if you move the disk to a different system the
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BIOS of that system might use a different geometry translation.
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.Pp
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If you run the equivalent of
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.Nm
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on a different operating system then the
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.Ar bootmenu
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strings associated with extended partitions may be lost.
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.Pp
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Editing an existing partition is risky, and may 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 works.
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This is completely safe as long as you answer the last question in the negative.
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You can also specify
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.Fl w Ar file
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to write the output to a file and later specify
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.Fl r Ar file
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to read back the updated information.
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This can be done without having write access to the disk volume.
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.Sh FILES
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.Bl -tag -width /usr/mdec/mbrxxxxxxxx -compact
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.It Pa /usr/mdec/mbr
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Default location of i386 bootcode
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.It Pa /usr/mdec/mbr_bootsel
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Default location of i386 bootselect code
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.It Pa /usr/mdec/mbr_ext
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Default location of i386 bootselect for extended partitions
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.El
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.Sh SEE ALSO
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.Xr disklabel 8 ,
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.Xr mbr 8 ,
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.Xr mbrlabel 8
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.Sh BUGS
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The word 'partition' is used to mean both an MBR partition and a
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.Nx
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partition, sometimes in the same sentence.
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.Pp
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There are subtleties that the program detects that are not explained in
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this manual page.
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