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).

   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
       disks, 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 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 or more.  To see the exact  val-
       the  specification for the desired partitioning of device from 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;  oth-
       erwise 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 partitions, 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, --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 disk(s).

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

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

       -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.
              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 disk.)

       --IBM, --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.   Sometimes  the
              last cylinder contains a bad sector table.

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

       -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  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 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.

              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 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 partition. 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  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

       The  <c,h,s>  parts  can (and probably should) be omitted - sfdisk com-
       putes them from <start> and <size> and the disk 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-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.

       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
       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 disk

       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 disk space after
       any DRDOS partition, I don't have any other problems with the two coex-
       isting 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'
       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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