fdisk -- Command

Hard-disk partitioning utility
/etc/fdisk [-r] [-c] [-b mboot] xdev ...

The command fdisk  lets you view how a hard  disk is partitioned, alter how
it is partitioned, and mark a partition so that the COHERENT bootstrap will
automatically boot the operating system  it contains.  If you wish, you can
use fdisk  to assign partitions  to different operating  systems, e.g., MS-
DOS, CP/M, Windows NT, COHERENT, and XENIX.

fdisk recognizes the following command-line options:

-b Use  the first  446 bytes  of the  file mboot  to replace  the bootstrap
   information in xdev. Use this option to overwrite the COHERENT bootstrap
   with another bootstrap.

-c Specify the  disk geometry (i.e.,  number of cylinders,  heads, sectors)
   for disk drives that your system's BIOS does not support.

-r Read-only  access.  fdisk  reads the  partition  table and  displays its
   contents, but does  not let you change how a  disk is partitioned.  This
   is the ``safe'' option.

-V Display the version number of fdisk.  PP When you invoke fdisk, it reads
   the  first  block  from   the  special  device  xdev,  which  holds  the
   partitioning information  for that disk.  xdev is  the device whose name
   ends in x; for example, if  you have one SCSI hard disk and one AT-style
   hard disk  installed in your machine, xdev would  be either /dev/sd0x or
   /dev/at0x. If you use fdisk with a device other than the x device (e.g.,
   with device  /dev/at0a), fdisk displays values  for your partitions that
   are totally bogus -- and probably quite alarming.

After you invoke  fdisk, it displays a warning message,  then the layout of
the disk  whose partition-table device you named on  the command line.  The
following gives an example layout, for a 33-megabyte AT disk:

    Drive 0 Currently has the following logical partitions:
                  [In Cylinders] [  In Tracks  ]
    Number  Type  Start End Size Start  End Size Mbyte Blocks Name
    0 Boot MS-DOS    0  149  150     0  899  900  7.83  15300 /dev/at0a
    1     EXT-DOS  150  614  464   900 3684 2784 24.28  47430 /dev/at0b
    2      UNUSED    0    0    0     0    0    0     0      0 /dev/at0c
    3      UNUSED    0    0    0     0    0    0     0      0 /dev/at0d

In this example, partition 1 (which is accessed via device /dev/at0a) holds
an MS-DOS file system.  It is marked as the ``Boot'' partition, which means
that the  COHERENT bootstrap will  boot its operating  system automatically
when you  reboot your computer.   The other columns  show the size  of each
partition, and its beginning and end points in both cylinders and tracks.

If you invoked  fdisk with its option -r, the  program exits at this point.
If you did not invoke it  with option -r, it displays the following menu of
actions:

    Possible actions:
       0 = Quit
       1 = Change active partition (or make no partition active)
       2 = Change one logical partition
       3 = Change all logical partitions
       4 = Delete one logical partition
       5 = Change drive characteristics
       6 = Display drive information
       7 = Proceed to next drive

The following describes each action in detail:

0. Quit fdisk.

1. Change which  partition is the active partition.  You  can also say that
   your  system  has no  active  partition.   If you  do  so, the  COHERENT
   bootstrap  will prompt  you at  boot  time to  enter the  number of  the
   partition whose  operating system you wish to boot.   fdisk will let you
   set only one active partition at a time.

2. Change the dimensions (i.e., the size, beginning point, or end point) of
   one partition.  Doing this destroys the data on that partition.

3. Change the dimensions of  every partition.  Doing this destroys the data
   on your hard disk.

4. Delete a partition.

5. Change the parameters of the drive.  Use this option if COHERENT somehow
   has a faulty  notion of your disk's size.  You  should never have to use
   this option; using it will wipe out all data on your hard disk.

6. Give summary information about the disk -- that is, re-display the table
   shown above.

7. This option appears only if you have more than one hard disk drive.  Use
   this  option to  display  information about  another hard  disk on  your
   system.

Before you change the dimensions of  any partition on your system, read the
warnings given  in the notes below.  When you  have finished modifying your
disk, fdisk then writes your changes into xdev.

Files

<fdisk.h>

See Also

commands,
hard disk,
ideinfo

Notes

If you change a device's  partition table, reboot your system.  Most device
drivers will not recognize the revised partition information until a reboot
occurs.

As the -r and -b options are contradictory, attempting to use them together
triggers an error message.

Note  that many  operating systems  implement a  program named  fdisk. Each
manipulates a  hard disk's  partition table, but  not all respect  the fact
that a  disk may hold more  than one operating system.   In particular, the
MS-DOS edition of fdisk can rearrange the order of entries in the partition
table.  If this happens, you may lose the ability to run COHERENT until the
table is restored to its previous  order.  A sign of this problem is seeing
the prompt AT boot? when you  try to start COHERENT after running any fdisk
program, and not being able to get past it.

Computer systems  that use  older releases of  a BIOS may  report incorrect
disk parameters.  Users of such systems should change the CMOS setup values
if  possible, but  the BIOS  on some  older systems will  not allow  you to
specify arbitrary values for  disk parameters.  Users with such systems can
use the option fdisk -c option instead.

If you plan  to install and run COHERENT and  MS-DOS on the same hard disk,
note the following:

-> If you wish  to install COHERENT and MS-DOS on  the same hard drive, you
   must run the MS-DOS fdisk first!

-> If you  plan on running both operating systems,  you must install MS-DOS
   first and leave some free cylinders  on the disk for COHERENT as well as
   a free partition.  You can have  both primary as well as extended MS-DOS
   partitions on the same drive as COHERENT, but COHERENT cannot use a sub-
   partition of  the MS-DOS extended partition.  COHERENT  must have one of
   the four real partitions.  Failure to observe these rules will result in
   loss of data!  Caveat utilitor.

© 2012 by Stephen A. Ness