Provided by: util-linux_2.20.1-5.1ubuntu20.9_amd64 
NAME
cfdisk - display or manipulate disk partition table
SYNOPSIS
cfdisk [-agvz] [-c cylinders] [-h heads] [-s sectors-per-track] [-P opt] [device]
DESCRIPTION
cfdisk is a curses/slang based program for partitioning any hard disk drive. Typical values of the
device argument are:
/dev/hda [default]
/dev/hdb
/dev/sda
/dev/sdb
/dev/sdc
/dev/sdd
In order to write the partition table cfdisk needs something called the `geometry' of the disk: the
number of `heads' and the number of `sectors per track'. Linux does not use any geometry, so if the disk
will not be accessed by other operating systems, you can safely accept the defaults that cfdisk chooses
for you. The geometry used by cfdisk is found as follows. First the partition table is examined, to see
what geometry was used by the previous program that changed it. If the partition table is empty, or
contains garbage, or does not point at a consistent geometry, the kernel is asked for advice. If nothing
works 255 heads and 63 sectors/track is assumed. The geometry can be overridden on the command line or by
use of the `g' command. When partitioning an empty large modern disk, picking 255 heads and 63
sectors/track is always a good idea. There is no need to set the number of cylinders, since cfdisk knows
the disk size.
Next, cfdisk tries to read the current partition table from the disk drive. If it is unable to figure
out the partition table, an error is displayed and the program will exit. This might also be caused by
incorrect geometry information, and can be overridden on the command line. Another way around this
problem is with the -z option. This will ignore the partition table on the disk.
The main display is composed of four sections, from top to bottom: the header, the partitions, the
command line and a warning line. The header contains the program name and version number followed by the
disk drive and its geometry. The partitions section always displays the current partition table. The
command line is the place where commands and text are entered. The available commands are usually
displayed in brackets. The warning line is usually empty except when there is important information to
be displayed. The current partition is highlighted with reverse video (or an arrow if the -a option is
given). All partition specific commands apply to the current partition.
The format of the partition table in the partitions section is, from left to right: Name, Flags,
Partition Type, Filesystem Type and Size. The name is the partition device name. The flags can be Boot,
which designates a bootable partition or NC, which stands for "Not Compatible with DOS or OS/2". DOS,
OS/2 and possibly other operating systems require the first sector of the first partition on the disk and
all logical partitions to begin on the second head. This wastes the second through the last sector of
the first track of the first head (the first sector is taken by the partition table itself). cfdisk
allows you to recover these "lost" sectors with the maximize command (m). Note: fdisk(8) and some early
versions of DOS create all partitions with the number of sectors already maximized. For more
information, see the maximize command below. The partition type can be one of Primary or Logical. For
unallocated space on the drive, the partition type can also be Pri/Log, or empty (if the space is
unusable). The filesystem type section displays the name of the filesystem used on the partition, if
known. If it is unknown, then Unknown and the hex value of the filesystem type are displayed. A special
case occurs when there are sections of the disk drive that cannot be used (because all of the primary
partitions are used). When this is detected, the filesystem type is displayed as Unusable. The size
field displays the size of the partition in megabytes (by default). It can also display the size in
sectors and cylinders (see the change units command below). If an asterisk (*) appears after the size,
this means that the partition is not aligned on cylinder boundaries.
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 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. Note:
BE EXTREMELY CAREFUL if you use the dd command, since a small typo can make all of the data on your disk
useless.
For best results, 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.
COMMANDS
cfdisk commands can be entered by pressing the desired key (pressing Enter after the command is not
necessary). Here is a list of the available commands:
b Toggle bootable flag of the current partition. This allows you to select which primary partition
is bootable on the drive.
d Delete the current partition. This will convert the current partition into free space and merge
it with any free space immediately surrounding the current partition. A partition already marked
as free space or marked as unusable cannot be deleted.
g Change the disk geometry (cylinders, heads, or sectors-per-track). WARNING: This option should
only be used by people who know what they are doing. A command line option is also available to
change the disk geometry. While at the change disk geometry command line, you can choose to
change cylinders (c), heads (h), and sectors per track (s). The default value will be printed at
the prompt which you can accept by simply pressing the Enter key, or you can exit without changes
by pressing the ESC key. If you want to change the default value, simply enter the desired value
and press Enter. The altered disk parameter values do not take effect until you return to the
main menu (by pressing Enter or ESC at the change disk geometry command line). If you change the
geometry such that the disk appears larger, the extra sectors are added at the end of the disk as
free space. If the disk appears smaller, the partitions that are beyond the new last sector are
deleted and the last partition on the drive (or the free space at the end of the drive) is made to
end at the new last sector.
h Print the help screen.
m Maximize disk usage of the current partition. This command will recover the unused space between
the partition table and the beginning of the partition, but at the cost of making the partition
incompatible with DOS, OS/2 and possibly other operating systems. This option will toggle between
maximal disk usage and DOS, OS/2, etc. compatible disk usage. The default when creating a
partition is to create DOS, OS/2, etc. compatible partitions.
n Create new partition from free space. If the partition type is Primary or Logical, a partition of
that type will be created, but if the partition type is Pri/Log, you will be prompted for the type
you want to create. Be aware that (1) there are only four slots available for primary partitions
and (2) since there can be only one extended partition, which contains all of the logical drives,
all of the logical drives must be contiguous (with no intervening primary partition). cfdisk next
prompts you for the size of the partition you want to create. The default size, equal to the
entire free space of the current partition, is displayed in megabytes. You can either press the
Enter key to accept the default size or enter a different size at the prompt. cfdisk accepts size
entries in megabytes (M) [default], kilobytes (K), cylinders (C) and sectors (S) by entering the
number immediately followed by one of (M, K, C or S). If the partition fills the free space
available, the partition is created and you are returned to the main command line. Otherwise, the
partition can be created at the beginning or the end of the free space, and cfdisk will ask you to
choose where to place the partition. After the partition is created, cfdisk automatically adjusts
the other partitions' partition types if all of the primary partitions are used.
p Print the partition table to the screen or to a file. There are several different formats for the
partition that you can choose from:
r Raw data format (exactly what would be written to disk)
s Partition table in sector order format
t Partition table in raw format
The raw data format will print the sectors that would be written to disk if a write command is
selected. First, the primary partition table is printed, followed by the partition tables
associated with each logical partition. The data is printed in hex byte by byte with 16 bytes per
line.
The partition table in sector order format will print the partition table ordered by sector
number. The fields, from left to right, are the number of the partition, the partition type, the
first sector, the last sector, the offset from the first sector of the partition to the start of
the data, the length of the partition, the filesystem type (with the hex value in parenthesis),
and the flags (with the hex value in parenthesis). In addition to the primary and logical
partitions, free and unusable space is printed and the extended partition is printed before the
first logical partition.
If a partition does not start or end on a cylinder boundary or if the partition length is not
divisible by the cylinder size, an asterisk (*) is printed after the non-aligned sector
number/count. This usually indicates that a partition was created by an operating system that
either does not align partitions to cylinder boundaries or that used different disk geometry
information. If you know the disk geometry of the other operating system, you could enter the
geometry information with the change geometry command (g).
For the first partition on the disk and for all logical partitions, if the offset from the
beginning of the partition is not equal to the number of sectors per track (i.e., the data does
not start on the first head), a number sign (#) is printed after the offset. For the remaining
partitions, if the offset is not zero, a number sign will be printed after the offset. This
corresponds to the NC flag in the partitions section of the main display.
The partition table in raw format will print the partition table ordered by partition number. It
will leave out all free and unusable space. The fields, from left to right, are the number of the
partition, the flags (in hex), the starting head, sector and cylinder, the filesystem ID (in hex),
the ending head, sector and cylinder, the starting sector in the partition and the number of
sectors in the partition. The information in this table can be directly translated to the raw
data format.
The partition table entries only have 10 bits available to represent the starting and ending
cylinders. Thus, when the absolute starting (ending) sector number is on a cylinder greater than
1023, the maximal values for starting (ending) head, sector and cylinder are printed. This is the
method used by OS/2, and thus fixes the problems associated with OS/2's fdisk rewriting the
partition table when it is not in this format. Since Linux and OS/2 use absolute sector counts,
the values in the starting and ending head, sector and cylinder are not used.
q Quit program. This will exit the program without writing any data to disk.
t Change the filesystem type. By default, new partitions are created as Linux partitions, but since
cfdisk can create partitions for other operating systems, change partition type allows you to
enter the hex value of the filesystem you desire. A list of the know filesystem types is
displayed. You can type in the filesystem type at the prompt or accept the default filesystem
type [Linux].
u Change units of the partition size display. It will rotate through megabytes, sectors and
cylinders.
W Write partition table to disk (must enter an upper case W). Since this might destroy data on the
disk, you must either confirm or deny the write by entering `yes' or `no'. If you enter `yes',
cfdisk will write the partition table to disk and the tell the kernel to re-read the partition
table from the disk. The re-reading of the partition table does not work in some cases, for
example for device-mapper devices. In particular case you need to inform kernel about new
partitions by partprobe(8), kpartx(8) or reboot the system.
Up Arrow
Down Arrow
Move cursor to the previous or next partition. If there are more partitions than can be displayed
on a screen, you can display the next (previous) set of partitions by moving down (up) at the last
(first) partition displayed on the screen.
CTRL-L Redraws the screen. In case something goes wrong and you cannot read anything, you can refresh
the screen from the main command line.
? Print the help screen.
All of the commands can be entered with either upper or lower case letters (except for Writes). When in
a sub-menu or at a prompt to enter a filename, you can hit the ESC key to return to the main command
line.
OPTIONS
-a Use an arrow cursor instead of reverse video for highlighting the current partition.
-g Do not use the geometry given by the disk driver, but try to guess a geometry from the partition
table.
-v Print the version number and copyright.
-z Start with zeroed partition table. This option is useful when you want to repartition your entire
disk. Note: this option does not zero the partition table on the disk; rather, it simply starts
the program without reading the existing partition table.
-c cylinders
-h heads
-s sectors-per-track
Override the number of cylinders, heads and sectors per track read from the BIOS. If your BIOS or
adapter does not supply this information or if it supplies incorrect information, use these
options to set the disk geometry values.
-P opt Prints the partition table in specified formats. opt can be one or more of "r", "s" or "t". See
the print command (above) for more information on the print formats.
EXIT STATUS
0: No errors; 1: Invocation error; 2: I/O error; 3: cannot get geometry; 4: bad partition table on disk.
SEE ALSO
fdisk(8), sfdisk(8), mkfs(8), parted(8), partprobe(8), kpartx(8)
BUGS
The current version does not support multiple disks.
AUTHOR
Kevin E. Martin (martin@cs.unc.edu)
AVAILABILITY
The cfdisk command is part of the util-linux package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
util-linux July 2009 CFDISK(8)