174 lines
5.1 KiB
Groff
174 lines
5.1 KiB
Groff
.\" $NetBSD: fdisk.8,v 1.8 1995/03/18 14:55:34 cgd Exp $
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.\"
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.Dd April 4, 1993
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.Dt FDISK 8
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.\" .Os BSD 4
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.Sh NAME
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.Nm fdisk
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.Nd DOS partition maintenance program
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.Sh SYNOPSIS
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.Nm
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.Op Fl aiu
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.Op Ar device
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.Sh PROLOGUE
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In order for the BIOS to boot the kernel, certain conventions must be
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adhered to.
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Sector 0 of the disk must contain boot code, a partition table, and a
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magic number.
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BIOS partitions can be used to break the disk up into several pieces.
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The BIOS brings in sector 0, verifies the magic number, and begins
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executing the code at the first byte.
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This code is turn searches the DOS partition table for an `active'
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partition.
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If one is found, the boot block from that partition is loaded and replaces
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the original boot block.
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Under DOS, you could have one or more partitions with one active.
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The DOS
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.Nm
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program can be used to divide space on the disk into partitions and set
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one active.
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.Pp
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The NetBSD program
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.Nm
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serves a similar purpose to the DOS program.
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When called with no arguments, it prints the sector 0 partition table.
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An example follows:
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.Bd -literal
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******* Working on device /dev/rwd0d *******
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parameters extracted from in-core disklabel are:
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cylinders=769 heads=15 sectors/track=33 (495 sectors/cylinder)
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parameters to be used for BIOS calculations are:
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cylinders=769 heads=15 sectors/track=33 (495 sectors/cylinder)
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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 0 is:
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sysid 165 (NetBSD)
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start 495, size 380160 (185 MB), flag 0
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beg: cylinder 1, head 0, sector 1
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end: cylinder 768, head 14, sector 33
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The data for partition 1 is:
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sysid 164 (unknown)
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start 378180, size 2475 (1 MB), flag 0
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beg: cylinder 764, head 0, sector 1
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end: cylinder 768, head 14, sector 33
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The data for partition 2 is:
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<UNUSED>
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The data for partition 3 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 MB), flag 80
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beg: cylinder 769, head 0, sector 2
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end: cylinder 197, head 14, sector 33
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.Ed
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.Pp
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The disk is divided into three partitions that happen to fill the disk.
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The second partition overlaps the end of the first.
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(Used for debugging purposes)
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.Bl -tag -width "cyl, sector and head"
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.It Em "sysid"
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is used to label the partition. NetBSD reserves the
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magic number 165 decimal (A5 in hex).
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.It Em "start and size"
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fields provide the start address
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and size of a partition in sectors.
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.It Em "flag 80"
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specifies that this is the active partition.
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.It Em "cyl, sector and head"
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fields are used to specify the beginning address
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and end address for the partition.
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.It Em "Note:"
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these numbers are calculated using BIOS's understanding of the disk geometry
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and saved in the bootblock.
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.El
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.Pp
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The flags
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.Fl i
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or
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.Fl u
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are used to indicate that the partition data is to be updated.
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The
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.Nm
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program will enter a conversational mode.
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This mode is designed not to change any data unless you explicitly tell it to;
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.Nm
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selects defaults for its questions to guarantee that behavior.
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.Pp
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It displays each partition and asks if you want to edit it.
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If you reply affirmatively,
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it will step through each field showing the old value
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and asking for a new one.
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When you are done with a partition,
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.Nm
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will display the information again and ask if it is correct.
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.Nm
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will then procede to the next entry.
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.Pp
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Getting the
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.Em cyl, sector,
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and
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.Em head
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fields correct is tricky.
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So by default,
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they will be calculated for you;
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you can specify them if you choose.
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.Pp
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After all the partitions are processed,
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you are given the option to change the
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.Em active
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partition.
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To change only the
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.Em active
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partition, you can use the
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.Fl a
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flag instead.
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.Pp
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Finally,
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when the all the data for the first sector has been accumulated,
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.Nm
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will ask if you really want to rewrite sector 0.
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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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The difference between the
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.Fl u
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flag and
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.Fl i
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flag is that
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the
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.Fl u
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flag just edits the fields as they appear on the disk, while the
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.Fl i
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flag is used to `initialize' sector 0.
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The
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.Fl i
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flag instructs
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.Nm
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to start by making the first 3 partitions empty, setting the last partition
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to use the whole disk for NetBSD, and marking the last partition active.
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.Sh NOTES
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The automatic calculation of starting cylinder etc. uses
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a set of figures that represent what the BIOS thinks is the
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geometry of the drive.
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These figures are by default taken from the incore disklabel, but
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.Nm
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gives you an opportunity to change them.
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This allows the user to create a bootblock that can work with drives
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that use geometry translation under the BIOS.
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.Pp
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If you hand craft your disk layout,
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please make sure that the NetBSD partition starts on a cylinder boundary.
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(This restriction may be changed in the future.)
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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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.Sh SEE ALSO
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.Xr disklabel 8
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.Sh BUGS
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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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