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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
	      Display version information and exit.

       -h, --help
	      Display help text and exit.

       -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[=device_or_number]
	      Switch on the bootable flag.

	      This option takes an optional argument.  When no option argument
	      is given, the command will list the  partitions  that  have  the
	      bootable	flag set for the device specified as command argument.
	      For example:

		  % sfdisk --activate /dev/sda

	      When a device name is given as option argument,  the  partitions
	      specified	 as  command  argument	will  have  the	 bootable flag
	      switched on.  Other partitions for the same device will have the
	      bootable	flag cleared.  For example, with the following command
	      the partitions 1 and 4 are set to be bootable, while 2 and 3 are

		  % sfdisk --activate=/dev/sda 1 4

	      If  only a single partition needs to be activated, then the par‐
	      tition number must be given as option argument, and  the	device
	      as command argument.  For example:

		  % sfdisk --activate=1 /dev/sda

	      The  activate  option is turned by default on when the program's
	      invocation name is activate.

       -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.)

       -U, --unhide device
	      Make various Microsoft partition types unhidden.	For full  list
	      see types output.

		  % sfdisk --list-types | grep Hidden

	      Notice that the Hidden NTFS WinRE (Windows Recovery Environment)
	      does not have non-hidden equivalent.

       --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.)

	      Partitions are in order.	See also warning section.

	      Partitions are not in order.  See also warning section.

	      All logical partitions are inside outermost extended.  See  also
	      warning section and chaining.

	      Some,  or	 none, of the logical partitions are not inside outer‐
	      most extended.  See also warning section and chaining.

	      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.

       -1, --one-only
	      Reserved option that does nothing currently.

       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)

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