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RedHat 9 (Linux i386) - man page for sfdisk (redhat section 8)

SFDISK(8)			    Linux Programmer's Manual				SFDISK(8)

       sfdisk - Partition table manipulator for Linux

       sfdisk [options] device
       sfdisk -s [partition]

       sfdisk  has  four  (main)  uses:  list  the  size of a partition, list the partitions on a
       device, check the partitions on a device, and - very dangerous - repartition a device.

   List Sizes
       sfdisk -s partition gives the size of partition in blocks. This may be useful  in  connec-
       tion  with  programs like mkswap or so. Here partition is usually something like /dev/hda1
       or /dev/sdb12, but may also be an entire disk, like /dev/xda.
	      % sfdisk -s /dev/hda9
       If the partition argument is omitted, sfdisk will list the sizes of  all  disks,  and  the
	      % sfdisk -s
	      /dev/hda: 208896
	      /dev/hdb: 1025136
	      /dev/hdc: 1031063
	      /dev/sda: 8877895
	      /dev/sdb: 1758927
	      total: 12901917 blocks

   List Partitions
       The second type of invocation: sfdisk -l [options] device will list the partitions on this
       device.	If the device argument is omitted, the partitions on all hard disks are listed.
       % sfdisk -l /dev/hdc

       Disk /dev/hdc: 16 heads, 63 sectors, 2045 cylinders
       Units = cylinders of 516096 bytes, blocks of 1024 bytes, counting from 0

	  Device Boot Start	End   #cyls   #blocks	Id  System
       /dev/hdc1	  0+	406	407-   205096+	83  Linux native
       /dev/hdc2	407	813	407    205128	83  Linux native
       /dev/hdc3	814    2044    1231    620424	83  Linux native
       /dev/hdc4	  0	  -	  0	    0	 0  Empty
       The trailing - and + signs indicate that rounding has taken place,  and	that  the  actual
       value is slightly less (more).  To see the exact values, ask for a listing with sectors as

   Check partitions
       The third type of invocation: sfdisk -V device will apply various  consistency  checks  to
       the  partition  tables  on device.  It prints `OK' or complains. The -V option can be used
       together with -l. In a shell script one might use sfdisk -V -q device which only returns a

   Create partitions
       The  fourth  type of invocation: sfdisk device will cause sfdisk to read the specification
       for the desired partitioning of device from its standard input, and  then  to  change  the
       partition  tables  on  that  disk. Thus, it is possible to use sfdisk from a shell script.
       When sfdisk determines that its standard input is a terminal, it will  be  conversational;
       otherwise it will abort on any error.


       As a precaution, one can save the sectors changed by sfdisk:
	      % sfdisk /dev/hdd -O hdd-partition-sectors.save

       Then,  if you discover that you did something stupid before anything else has been written
       to disk, it may be possible to recover the old situation with
	      % sfdisk /dev/hdd -I hdd-partition-sectors.save

       (This is not the same as saving the old partition table: a readable  version  of  the  old
       partition  table  can  be saved using the -d option. However, if you create logical parti-
       tions, the sectors describing them are located somewhere on disk, possibly on sectors that
       were  not part of the partition table before. Thus, the information the -O option saves is
       not a binary version of the output of -d.)

       There are many options.

       -v or --version
	      Print version number of sfdisk and exit immediately.

       -? or --help
	      Print a usage message and exit immediately.

       -T or --list-types
	      Print the recognized types (system Id's).

       -s or --show-size
	      List the size of a partition.

       -g or --show-geometry
	      List the kernel's idea of the geometry of the indicated disk(s).

       -l or --list
	      List the partitions of a device.

       -d     Dump the partitions of a device in a format useful as input to sfdisk. For example,
		  % sfdisk -d /dev/hda > hda.out
		  % sfdisk /dev/hda < hda.out
	      will correct the bad last extended partition that the OS/2 fdisk creates.

       -V or --verify
	      Test whether partitions seem correct. (See above.)

       -i or --increment
	      Number cylinders etc. starting from 1 instead of 0.

       -N number
	      Change only the single partition indicated. For example:
		  % sfdisk /dev/hdb -N5
	      will make the fifth partition on /dev/hdb bootable (`active')  and  change  nothing
	      else.  (Probably this fifth partition is called /dev/hdb5, but you are free to call
	      it something else, like `/my_equipment/disks/2/5' or so).

	      Make the indicated partition(s) active, and all others inactive.

       -c or --id number [Id]
	      If no Id argument given: print the partition Id of the indicated partition.  If  an
	      Id  argument  is	present:  change  the type (Id) of the indicated partition to the
	      given value.  This option has the two very long forms --print-id	and  --change-id.
	      For example:
		  % sfdisk --print-id /dev/hdb 5
		  % sfdisk --change-id /dev/hdb 5 83
	      first reports that /dev/hdb5 has Id 6, and then changes that into 83.

       -uS or -uB or -uC or -uM
	      Accept  or report in units of sectors (blocks, cylinders, megabytes, respectively).
	      The default is cylinders, at least when the geometry is known.

       -x or --show-extended
	      Also list non-primary extended partitions on output,  and  expect  descriptors  for
	      them on input.

       -C cylinders
	      Specify the number of cylinders, possibly overriding what the kernel thinks.

       -H heads
	      Specify the number of heads, possibly overriding what the kernel thinks.

       -S sectors
	      Specify the number of sectors, possibly overriding what the kernel thinks.

       -f or --force
	      Do what I say, even if it is stupid.

       -q or --quiet
	      Suppress warning messages.

       -L or --Linux
	      Do not complain about things irrelevant for Linux.

       -D or --DOS
	      For  DOS-compatibility: waste a little space.  (More precisely: if a partition can-
	      not contain sector 0, e.g. because that is the MBR of the device, or  contains  the
	      partition  table of an extended partition, then sfdisk would make it start the next
	      sector. However, when this option is given it skips to the start of the next track,
	      wasting  for  example  33  sectors (in case of 34 sectors/track), just like certain
	      versions of DOS do.)  Certain Disk Managers and boot loaders (such as OSBS, but not
	      LILO  or	the  OS/2  Boot Manager) also live in this empty space, so maybe you want
	      this option if you use one.

       -E or --DOS-extended
	      Take the starting sector numbers of "inner" extended partitions to be  relative  to
	      the  starting  cylinder  boundary  of the outer one, (like some versions of DOS do)
	      rather than to the starting sector (like Linux does).  (The fact that  there  is	a
	      difference  here	means  that  one  should  always let extended partitions start at
	      cylinder boundaries if DOS and Linux should interpret the partition  table  in  the
	      same way.  Of course one can only know where cylinder boundaries are when one knows
	      what geometry DOS will use for this disk.)

       --IBM or --leave-last
	      Certain IBM diagnostic programs assume that they can use the  last  cylinder  on	a
	      disk  for disk-testing purposes. If you think you might ever run such programs, use
	      this option to tell sfdisk that it should not allocate the  last	cylinder.   Some-
	      times the last cylinder contains a bad sector table.

       -n     Go through all the motions, but do not actually write to disk.

       -R     Only  execute the BLKRRPART ioctl (to make the kernel re-read the partition table).
	      This can be useful for checking in advance that the final BLKRRPART  will  be  suc-
	      cessful,	and  also  when you changed the partition table `by hand' (e.g., using dd
	      from a backup).  If the kernel complains (`device busy for  revalidation	(usage	=
	      2)')  then something still uses the device, and you still have to unmount some file
	      system, or say swapoff to some swap partition.

	      When starting a repartitioning of a disk, sfdisk	checks	that  this  disk  is  not
	      mounted,	or in use as a swap device, and refuses to continue if it is. This option
	      suppresses the test. (On the other hand, the -f option would force sfdisk  to  con-
	      tinue even when this test fails.)

       -O file
	      Just  before  writing  the  new  partition, output the sectors that are going to be
	      overwritten to file (where hopefully file resides on another disk, or on a floppy).

       -I file
	      After destroying your filesystems with an unfortunate  sfdisk  command,  you  would
	      have  been able to restore the old situation if only you had preserved it using the
	      -O flag.

       Block 0 of a disk (the Master Boot Record) contains  among  other  things  four	partition
       descriptors. The partitions described here are called primary partitions.

       A partition descriptor has 6 fields:
	      struct partition {
		  unsigned char bootable;	 /* 0 or 0x80 */
		  hsc begin_hsc;
		  unsigned char id;
		  hsc end_hsc;
		  unsigned int starting_sector;
		  unsigned int nr_of_sectors;

       The two hsc fields indicate head, sector and cylinder of the begin and the end of the par-
       tition. Since each hsc field only takes 3 bytes, only 24 bits are  available,  which  does
       not  suffice  for big disks (say > 8GB). In fact, due to the wasteful representation (that
       uses a byte for the number of heads, which is typically 16), problems already  start  with
       0.5GB.  However Linux does not use these fields, and problems can arise only at boot time,
       before Linux has been started. For more details, see the lilo documentation.

       Each partition has a type, its `Id', and if this type is 5 or f (`extended partition') the
       starting  sector  of the partition again contains 4 partition descriptors. MSDOS only uses
       the first two of these: the first one an actual data partition, and the second  one  again
       an  extended  partition	(or empty).  In this way one gets a chain of extended partitions.
       Other operating systems have slightly different conventions.  Linux also accepts  type  85
       as  equivalent  to  5  and f - this can be useful if one wants to have extended partitions
       under Linux past the 1024 cylinder boundary, without DOS FDISK hanging.	(If there  is  no
       good reason, you should just use 5, which is understood by other systems.)

       Partitions  that  are  not primary or extended are called logical.  Often, one cannot boot
       from logical partitions (because the process of finding them is more  involved  than  just
       looking	at  the  MBR).	 Note that of an extended partition only the Id and the start are
       used. There are various conventions about what to write in the other  fields.  One  should
       not try to use extended partitions for data storage or swap.

       sfdisk reads lines of the form
	      <start> <size> <id> <bootable> <c,h,s> <c,h,s>
       where each line fills one partition descriptor.

       Fields are separated by whitespace, or comma or semicolon possibly followed by whitespace;
       initial and trailing whitespace is ignored.  Numbers can be octal, decimal or hexadecimal,
       decimal is default.  When a field is absent or empty, a default value is used.

       The <c,h,s> parts can (and probably should) be omitted - sfdisk computes them from <start>
       and <size> and the disk geometry as given by the kernel or specified using the -H, -S,  -C

       Bootable is specified as [*|-], with as default not-bootable.  (The value of this field is
       irrelevant for Linux - when Linux runs it has been booted already - but might play a  role
       for  certain  boot  loaders  and for other operating systems.  For example, when there are
       several primary DOS partitions, DOS assigns C: to the first among these that is bootable.)

       Id is given in hex, without the 0x prefix, or is [E|S|L|X], where L (LINUX_NATIVE (83)) is
       the  default,  S  is LINUX_SWAP (82), E is EXTENDED_PARTITION (5), and X is LINUX_EXTENDED

       The default value of start is the first nonassigned sector/cylinder/...

       The default value of size is as much as possible (until next partition or end-of-disk).

       However, for the four partitions inside an extended partition,  the  defaults  are:  Linux
       partition, Extended partition, Empty, Empty.

       But  when  the  -N  option (change a single partition only) is given, the default for each
       field is its previous value.

       The command
	      sfdisk /dev/hdc << EOF
       will partition /dev/hdc just as indicated above.

       With the -x option, the number of input lines must be a multiple of 4: you  have  to  list
       the two empty partitions that you never want using two blank lines. Without the -x option,
       you give one line for the partitions inside a extended partition,  instead  of  four,  and
       terminate  with end-of-file (^D).  (And sfdisk will assume that your input line represents
       the first of four, that the second one is extended, and the 3rd and 4th are empty.)

       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

       The  bottom  line  is  that  if you use sfdisk 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 sfdisk to make a
       DOS partition table entry for /dev/hda1, then (after exiting sfdisk 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.   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 exam-
       ple,  you  should make DOS partitions with the DOS FDISK program and Linux partitions with
       the Linux sfdisk program.

       Stephen Tweedie reported (930515): `Most reports of superblock corruption turn out  to  be
       due  to	bad  partitioning, with one filesystem overrunning the start of the next and cor-
       rupting its superblock.	I have even had this problem with the supposedly-reliable  DRDOS.
       This  was quite possibly due to DRDOS-6.0's FDISK command.  Unless I created a blank track
       or cylinder between the DRDOS partition and the immediately  following  one,  DRDOS  would
       happily	stamp  all  over  the start of the next partition.  Mind you, as long as I keep a
       little free disk space after any DRDOS partition, I don't have any other problems with the
       two coexisting on the one drive.'

       A.  V.  Le  Blanc writes in README.esfdisk: `Dr. DOS 5.0 and 6.0 has been reported to have
       problems cooperating with Linux, and with this version  of  efdisk  in  particular.   This
       efdisk  sets  the system type to hexadecimal 81.  Dr. DOS seems to confuse this with hexa-
       decimal 1, a DOS code.  If you use Dr. DOS, use the efdisk command 't' to change the  sys-
       tem code of any Linux partitions to some number less than hexadecimal 80; I suggest 41 and
       42 for the moment.'

       A. V. Le Blanc writes in his README.fdisk: `DR-DOS 5.0 and 6.0 are reported to have diffi-
       culties	with  partition ID codes of 80 or more.  The Linux `fdisk' used to set the system
       type of new partitions to hexadecimal 81.  DR-DOS seems to confuse this	with  hexadecimal
       1,  a  DOS code.  The values 82 for swap and 83 for file systems should not cause problems
       with DR-DOS.  If they do, you may use the `fdisk' command `t' to change the system code of
       any  Linux partitions to some number less than hexadecimal 80; I suggest 42 and 43 for the

       In fact, it seems that only 4 bits are significant for the DRDOS FDISK, so that for  exam-
       ple  11	and 21 are listed as DOS 2.0. However, DRDOS itself seems to use the full byte. I
       have not been able to reproduce any corruption with DRDOS or its fdisk.

       A corresponding interactive cfdisk (with curses interface) is still lacking.

       There are too many options.

       There is no support for non-DOS partition types.

       A. E. Brouwer (aeb@cwi.nl)

       cfdisk(8), fdisk(8), mkfs(8), parted(8)

Linux 1.3.23				 1 September 1995				SFDISK(8)

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