path: root/disk-utils/fdisk.8

.\" Copyright 1992, 1993 Rickard E. Faith (faith@cs.unc.edu)
.\" May be distributed under the GNU General Public License
.TH FDISK 8 "Tue Mar 22 01:00:00 1994" "Linux 1.0" "Linux Programmer's Manual"
.SH NAME
fdisk \- Partition table manipulator for Linux
.SH SYNOPSIS
.B fdisk
.B "[ \-l ] [ \-v ] [ \-s partition] ["
device
.B ]
.SH DESCRIPTION
.B fdisk
is a menu driven program for manipulation of the hard disk partition table.
The
.I device
is usually one of the following:
.sp
.nf
.RS
/dev/hda
/dev/hdb
/dev/sda
/dev/sdb
.RE
.fi
The
.I partition
is a
.I device
name followed by a partition number.  For example,
.B /dev/hda1
is the first partition on the first hard disk in the system.

If possible,
.B fdisk
will obtain the disk geometry automatically.  This is
.I not
necessarily the
.I physical
disk geometry, but is the disk geometry that MS-DOS uses for the partition
table.  If
.B fdisk
warns you that you need to set the disk geometry, please believe this
statement, and set the geometry.  This should only be necessary with
certain SCSI host adapters (the drivers for which are rapidly being
modified to provide geometry information automatically).

Whenever a partition table is printed out, a consistency check is performed
on the partition table entries.  This check verifies that the physical and
logical start and end points are identical, and that the partition starts
and ends on a cylinder boundary (except for the first partition).

Old versions of fdisk (all versions prior to 1.1r [including 0.93])
incorrectly mapped the cylinder/head/sector specification onto absolute
sectors.  This may result in the first partition on a drive failing the
consistency check.  If you use LILO to boot, this situation can be ignored.
However, there are reports that the OS/2 boot manager will not boot a
partition with inconsistent data.

Some versions of MS-DOS create a first partition which does not begin
on a cylinder boundary, but on sector 2 of the first cylinder.
Partitions beginning in cylinder 1 cannot begin on a cylinder boundary, but
this is unlikely to cause difficulty unless you have OS/2 on your machine.

In version 1.1r, a BLKRRPART ioctl() is performed before exiting when the
partition table is updated.  This is primarily to ensure that removable
SCSI disks have their partition table information updated.  If the kernel
does not update its partition table information, fdisk warns you to
reboot.  If you do not reboot your system after receiving such a warning,
you may lose or corrupt the data on the disk.  Sometimes BLKRRPART fails
silently, when installing Linux, you should
.I always
reboot after editing the partition table.

.SH "DOS 6.x WARNING"

The DOS 6.x FORMAT command looks for some information in the first
sector of the data area of the partition, and treats this information
as more reliable than the information in the partition table.  DOS
FORMAT expects DOS FDISK to clear the first 512 bytes of the data area
of a partition whenever a size change occurs.  DOS FORMAT will look at
this extra information even if the /U flag is given -- we consider
this a bug in DOS FORMAT and DOS FDISK.

The bottom line is that if you use cfdisk or fdisk to change the size of a
DOS partition table entry, then you must also use
.B dd
to zero the first 512 bytes of that partition before using DOS FORMAT to
format the partition.  For example, if you were using cfdisk to make a DOS
partition table entry for /dev/hda1, then (after exiting fdisk or cfdisk
and rebooting Linux so that the partition table information is valid) you
would use the command "dd if=/dev/zero of=/dev/hda1 bs=512 count=1" to zero
the first 512 bytes of the partition.
.B BE EXTREMELY CAREFUL
if you use the
.B dd
command, since a small typo can make all of the data on your disk useless.

.B BE EXTREMELY CAREFUL
if you use the
.B dd
command, since a small typo can make all of the data on your disk useless.

For best resutls, you should always use an OS-specific partition table
program.  For example, you should make DOS partitions with the DOS FDISK
program and Linux partitions with the Linux fdisk or Linux cfdisk program.

.SH OPTIONS
.TP
.B \-v
Prints version number of
.B fdisk
program.
.TP
.B \-l
Lists the partition tables for
.BR /dev/hda ,
.BR /dev/hdb ,
.BR /dev/sda ,
.BR /dev/sdb ,
.BR /dev/sdc ,
.BR /dev/sdd ,
.BR /dev/sde ,
.BR /dev/sdf ,
.BR /dev/sdg ,
.BR /dev/sdh ,
and then exits.
.TP
.BI \-s partition
If the
.I partition
is not a DOS partition (i.e., the partition id is greater than 10), then
the
.I size
of that partition is printed on the standard output.  This value is
normally used as an argument to the
.BR mkfs (8)
program to specify the size of the partition which will be formatted.
.SH BUGS
Although this man page (written by faith@cs.unc.edu) is poor, there is
.I excellent
documentation in the README.fdisk file (written by LeBlanc@mcc.ac.uk) that
should always be with the fdisk distribution.  If you cannot find this file
in the
.I util-linux-*
directory or with the
.I fdisk.c
source file, then you should write to the distributor of your version of
.B fdisk
and complain that you do not have all of the available documentation.
.SH AUTHOR
A. V. Le Blanc (LeBlanc@mcc.ac.uk)
.br
v1.0r: SCSI and extfs support added by Rik Faith (faith@cs.unc.edu)
.br
v1.1r: Bug fixes and enhancements by Rik Faith (faith@cs.unc.edu), with
special thanks to Michael Bischoff (i1041905@ws.rz.tu-bs.de or
mbi@mo.math.nat.tu-bs.de).
.br
v1.3: Latest enhancements and bug fixes by A. V. Le Blanc, including the
addition of the
.B \-s
option.
.bt
v2.0: Disks larger than 2GB are now fully supported, thanks to Remy Card's
llseek support.