178 lines
5.0 KiB
Groff
178 lines
5.0 KiB
Groff
.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 maintainance program
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.Sh SYNOPSIS
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.Nm
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.Op Fl i
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.Op Fl u
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.Bl -tag -width time
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.It Fl i
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Initializes sector 0 of the disk.
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.It Fl u
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Is used for updating (editing) sector 0 of the disk.
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.El
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.Sh PROLOGUE
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In order for the BIOS to boot the kernel,
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certain conventions must be adhered to.
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Sector 0 of the disk must contain boot code,
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a partition table,
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and a magic number.
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BIOS partitions can be used to break the disk up into several pieces.
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The BIOS brings in sector 0
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(does it really use the code?)
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and verifies the magic number.
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It then searches the 4 BIOS partitions described by sector 0
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to determine which of them is
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.Em active.
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This boot then brings in the secondary boot block from the
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.Em active
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partition and runs it.
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Under DOS,
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you could have one or more partitions with one
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.Em active.
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The DOS
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.Nm
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program can be used to divide space on the disk into partitions and set one
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.Em active.
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.Sh DESCRIPTION
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The 386bsd 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 blks/cyl)
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parameters to be used for BIOS calculations are:
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cylinders=769 heads=15 sectors/track=33 (495 blks/cyl)
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Warning: BIOS sector numbering starts with sector 1
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Information from DOS bootblock is:
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The data for partition 0 is:
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sysid 165,(386BSD)
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start 495, size 380160 (185 Meg), flag 0
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beg: cyl 1/ sector 1/ head 0;
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end: cyl 768/ sector 33/ head 14
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The data for partition 1 is:
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sysid 164,(unknown)
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start 378180, size 2475 (1 Meg), flag 0
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beg: cyl 764/ sector 1/ head 0;
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end: cyl 768/ sector 33/ head 14
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The data for partition 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 Meg), flag 80
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beg: cyl 769/ sector 2/ head 0;
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end: cyl 197/ sector 33/ head 14
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.Ed
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.Pp
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The disk is divided into three parititions 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. 386bsd 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 parition 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 parititon.
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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 paritition 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 the above behaviour.
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.Pp
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It displays each partition
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and ask if you want to edit it.
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If you say yes,
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it will step through each field showing the old value
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and asking for a new one.
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When you are done with a partition,
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.Nm
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will display it and ask if it is correct.
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.Nm
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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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Finally,
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when the all the data for the first sector has been accumulated,
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you are asked if you really want to rewrite sector 0.
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Only if you answer yes,
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will the data be written to disk.
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.Pp
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The difference between the
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.Fl u
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flag and
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.Fl i
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flag is that
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the
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.Fl u
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flag just edits the fields as they appear on the disk.
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While the
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.Fl i
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flag is used to "initialize" sector 0;
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it will setup the last BIOS partition to use the whole disk for 386bsd;
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and make it active.
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.Sh NOTES
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.Pp
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The automatic calculation of starting cylinder etc. uses
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a set of figures that represent what the BIOS thinks is the
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geometry of the drive.
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These figures are by default taken from the incore disklabel,
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but the program initially gives you an oportunity 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 386bsd partition starts on a cylinder boundary.
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A number of decisions made later may assume this.
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(This might not be necessary later.)
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.Pp
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Editing an existing partition will most likely cause you to
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lose all the data in that partition.
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.Pp
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You should run this program interactively once or twice to see how it works.
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This is completely safe as long as you answer the last question in the negative.
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There are subtleties
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that the program detects
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that are not fully explained in this manual page.
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.Sh SEE ALSO
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.Xr disklabel 8
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.Sh BUGS
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One less now, but probably more
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