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SFDISK(8)		     System Administration		     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.

       sfdisk  doesn't understand the GUID Partition Table (GPT) format and it
       is not designed for large partitions.  In  these	 cases	use  the  more
       advanced GNU parted(8).

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

   List sizes
       sfdisk -s partition gives the size of partition in blocks.  This may be
       useful  in  connection with programs like mkswap(8).  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
       block devices, and the total:

	      % 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 device will  list  the	parti-
       tions  on the specified device.	If the device argument is omitted, the
       partitions on all block devices 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 or more.	 To see the exact val-
       ues, ask for a listing with sectors as unit (-u S).

   Check partitions
       The third type of invocation: sfdisk -V device will apply various  con-
       sistency	 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 status.

   Create partitions
       The  fourth type of invocation: sfdisk device will cause sfdisk to read
       the specification for the desired partitioning of device from  standard
       input,  and  then  to change the partition tables on that block device.
       Thus it is possible to use sfdisk from a	 shell	script.	  When	sfdisk
       determines  that its standard input is a terminal, it will be conversa-
       tional; 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  the  block	 device, 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 partitions, the sectors describing  them
       are  located  somewhere	on block device, 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, --version
	      Print version number of sfdisk and exit immediately.

       -h, --help
	      Print a usage message and exit immediately.

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

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

       -g, --show-geometry
	      List  the	 kernel's  idea of the geometry of the indicated block

       -G, --show-pt-geometry
	      List the geometry of the	indicated  block  devices  guessed  by
	      looking at the partition table.

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

       -d, --dump
	      Dump  the	 partitions  of a device in a format that is usable 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

       -V, --verify
	      Test whether partitions seem correct.  (See the third invocation
	      type above.)

       -i, --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).

       -A, --activate number
	      Make the indicated partition(s) active, and all others inactive.

       -c, --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
	      two longer 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.

       -u, --unit letter
	      Interpret	 the  input and show the output in the units specified
	      by letter.  This letter can be one of S, C, B or M, meaning Sec-
	      tors,   Cylinders,  Blocks  and  Megabytes,  respectively.   The
	      default is cylinders, at least when the geometry is known.

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

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

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

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

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

       -q, --quiet
	      Suppress warning messages.

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

       -D, --DOS
	      For DOS-compatibility: waste a little space.   (More  precisely:
	      if a partition cannot 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, --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 relative to the
	      actual 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 block device.)

       --IBM, --leave-last
	      Certain  IBM  diagnostic	programs  assume that they can use the
	      last cylinder on a device 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.  Sometimes
	      the last cylinder contains a bad sector table.

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

       -R, --re-read
	      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 successful, 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 block device, sfdisk checks
	      that this device 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 continue
	      even when this test fails.)

	      Caution, see warning section.  To be documented.

	      Caution, see warning section.  To be documented.

	      Caution, see warning section.  Chaining order.

	      Caution, see warning section.  Chaining order.

	      Caution,	see  warning section.  Every partition is contained in
	      the surrounding partitions and is disjoint from all others.

	      Caution, see warning section.  Every data partition is contained
	      in  the surrounding partitions and disjoint from all others, but
	      extended partitions may  lie  outside  (insofar  as  allowed  by

	      Caution,	see warning section.  All data partitions are mutually
	      disjoint; extended partitions each use one sector	 only  (except
	      perhaps for the outermost one).

       -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 block device, 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 block device (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 partition. Since each hsc field only takes 3 bytes, only
       24  bits	 are  available,  which does not suffice for big block devices
       (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	 prob-
       lems  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 con-
       tains 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

       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 vari-
       ous 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 fol-
       lowed by whitespace; initial and trailing whitespace is ignored.	  Num-
       bers  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  com-
       putes  them  from  <start>  and <size> and the block device geometry as
       given by the kernel or specified using the -H, -S, -C flags.

       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

       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

       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-device).

       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.

       A '+' can be specified instead of a number for  size,  which  means  as
       much as possible. This is useful with the -N option.

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

       The command
	      sfdisk /dev/hdb << EOF
       will  partition	/dev/hdb  into two Linux partitions of 3 and 60 cylin-
       ders, a swap space of 19 cylinders, and an extended partition  covering
       the  rest.  Inside  the extended partition there are four Linux logical
       partitions, three of 130 cylinders and one covering the rest.

       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	parti-
       tions  inside a extended partition, instead of four, and terminate with
       end-of-file (^D).  (And sfdisk will assume that your input line	repre-
       sents  the  first of four, that the second one is extended, and the 3rd
       and 4th are empty.)

       The options marked with caution in the manual page are dangerous.   For
       example not all functionality is completely implemented, which can be a
       reason for unexpected results.

       The DOS 6.x FORMAT command looks for some information in the first sec-
       tor  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 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	parti-
       tion.   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	 block
       device 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 sfdisk program.

       Stephen	Tweedie reported (930515): `Most reports of superblock corrup-
       tion turn out to be due to bad partitioning, with one filesystem	 over-
       running	the  start  of the next and corrupting 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	 device	 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.efdisk: `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 hexadeci-
       mal  81.	 Dr. DOS seems to confuse this with hexadecimal 1, a DOS code.
       If you use Dr. DOS, use the efdisk command 't'  to  change  the	system
       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  difficulties 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 moment.'

       In fact, it seems that only 4 bits are significant for the DRDOS FDISK,
       so that for example 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.

       There are too many options.

       There is no support for non-DOS partition types.

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

       The sfdisk command is part of the util-linux package and	 is  available
       from ftp://ftp.kernel.org/pub/linux/utils/util-linux/.

util-linux			  August 2011			     SFDISK(8)