Computer Science
CFDISK(8) Linux Programmer's Manual CFDISK(8)
NAME
cfdisk - Curses based disk partition table manipulator for
Linux
SYNOPSIS
cfdisk [ -avz ] [ -c cylinders ] [ -h heads ] [ -s sec-
tors-per-track ] [ -P opt ] [ device ]
DESCRIPTION
cfdisk is a curses based program for partitioning a hard
disk drive. The device can be any one of the following:
/dev/hda [default]
/dev/hdb
/dev/sda
/dev/sdb
/dev/sdc
/dev/sdd
cfdisk first tries to read the geometry of the hard disk.
If it fails, an error message is displayed and cfdisk
exits. This should only happen when partitioning a SCSI
drive on an adapter without a BIOS. To correct this prob-
lem, you can set the cylinders, heads and sectors-per-
track on the command line. 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 dis-
played and the program will exit. This might also be
caused by incorrect geometry information, and can be over-
ridden on the command line. Another way around this prob-
lem 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 geome-
try. The partitions section always displays the current
partition table. The command line is the place where com-
mands and text are entered. The available commands are
usually displayed in brackets. The warning line is usu-
ally 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 par-
tition.
The format of the partition table in the partitions sec-
tion 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 maxi-
mized. For more information, see the maximize command
below. The partition type can be one of Primary or Logi-
cal. For unallocated space on the drive, the partition
type can also be Pri/Log, or empty (if the space is unus-
able). 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 bound-
aries.
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 informa-
tion in the partition table. DOS FORMAT expects DOS FDISK
to clear the first 512 bytes of the data area of a parti-
tion 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 par-
tition before using DOS FORMAT to format the partition.
For example, if you were using cfdisk to make a DOS parti-
tion 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 sec-
tors-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, sim-
ply 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.
h Print the help screen.
m Maximize disk usage of the current partition. This
command will recover the the unused space between
the partition table and the beginning of the parti-
tion, 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 par-
tition 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 parti-
tion, 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 immedi-
ately followed by one of (M, K, C or S). If the
partition fills the free space available, the par-
tition is created and you are returned to the main
command line. Otherwise, the partition can be cre-
ated 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.
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 writ-
ten 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 associ-
ated 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 sec-
tor, 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 parti-
tion 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 divisi-
ble 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 dif-
ferent 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 begin-
ning 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 (end-
ing) 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 parti-
tion table when it is not in this format. Since
Linux and OS/2 use absolute sector counts, the val-
ues 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 parti-
tions 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 cylin-
ders.
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 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.
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.
-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 parti-
tion 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)
BUGS
The current version does not support multiple disks.
AUTHOR
Kevin E. Martin (martin@cs.unc.edu)
The BOGUS Linux Release 3 June 1995 1
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