cfdisk — Curses based disk partition table manipulator for Linux
cfdisk [−agvz] [ −c cylinders ] [ −h heads ] [ −s sectors−per−track ] [
−P opt ] [device]
cfdisk is a
curses 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
asterisks (*) appears after the
size, this means that the partition is not aligned on
cylinder boundaries.
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.
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:
bToggle bootable flag of the current partition. This allows you to select which primary partition is bootable on the drive.
dDelete 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.
gChange 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 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.
hPrint the help screen.
mMaximize disk usage of the current partition. This command will recover the 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.
nCreate 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 display 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 partition's partition types if all of
the primary partitions are used.
pPrint the partition table to the screen or to a file. There are several different formats for the partition that you can choose from:
rRaw data format (exactly what would be written to disk)
sPartition table in sector order format
tPartition 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 asterisks (
*) 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 theNCflag 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.
qQuit program. This will exit the program without writing any data to disk.
tChange 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].
uChange units of the partition size display. It will rotate through megabytes, sectors and cylinders.
WWrite 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 works is most cases, but I have seen it fail. Don't panic. It will be correct after you reboot the system. In all cases, I still recommend rebooting the system--just to be safe.
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-LRedraws 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.
−aUse an arrow cursor instead of reverse video for highlighting the current partition.
−gDo not use the geometry given by the disk driver, but try to guess a geometry from the partition table.
−vPrint the version number and copyright.
−zStart 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−trackOverride 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
optPrints 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.
0: No errors; 1: Invocation error; 2: I/O error; 3: cannot get geometry; 4: bad partition table on disk.
Kevin E. Martin (martin@cs.unc.edu)
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cfdisk.8 -- man page for cfdisk Copyright 1994 Kevin E. Martin (martincs.unc.edu) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. " for hilit mode |