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CFDISK(8) System Administration CFDISK(8)

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-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


Note that cfdisk does not align partitions to block device
    I/O limits. This functionality is provided by fdisk(8).


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:



  

  
Toggle bootable flag of the current partition. This allows you to select
      which primary partition is bootable on the drive.

  

  
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.

  

  
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.

  

  
Print the help screen.

  

  
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.

  

  
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.

  

  
Print the partition table to the screen or to a file. There are several
      different formats for the partition that you can choose from:
    

  







  

  
Raw data format (exactly what would be written to disk)

  

  
Partition table in sector order format

  

  
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.





  

  
Quit program. This will exit the program without writing any data to
    disk.

  

  
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].

  

  
Change units of the partition size display. It will rotate through
      megabytes, sectors and cylinders.

  

  
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.

  

  

  

  
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.

  

  
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



  

  
Use an arrow cursor instead of reverse video for highlighting the current
      partition.

  

  
Do not use the geometry given by the disk driver, but try to guess a
      geometry from the partition table.

  

  
Print the version number and copyright.

  

  
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.

  

  

  

  

  

  
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.

  

  
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/.







  

    July 2009
    util-linux