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Linux 2.6 - man page for sfdisk (linux section 8)

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

NAME
       sfdisk - Partition table manipulator for Linux

SYNOPSIS
       sfdisk [options] device
       sfdisk -s [partition]

DESCRIPTION
       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 GUID Partition Table (GPT) and it is not designed for large par-
       titions. In particular case use more advanced GNU parted(8).

   List Sizes
       sfdisk  -s  partition gives the size of partition in blocks. This may be useful in connec-
       tion with programs like	mkswap(8)  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
	      81599
	      %
       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 [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
       unit.

   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
       status.

   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.

       BE EXTREMELY CAREFUL - ONE TYPING MISTAKE AND ALL YOUR DATA IS LOST

       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.

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).

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

       -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).

       -A number
	      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
		  6
		  % sfdisk --change-id /dev/hdb 5 83
		  OK
	      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.

       --no-reread
	      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.

THEORY
       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.

INPUT FORMAT
       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
       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 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
       (85).

       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.

EXAMPLE
       The command
	      sfdisk /dev/hdc << EOF
	      0,407
	      ,407
	      ;
	      ;
	      EOF
       will partition /dev/hdc just as indicated above.

       The command
	      sfdisk /dev/hdb << EOF
	      ,3,L
	      ,60,L
	      ,19,S
	      ,,E
	      ,130,L
	      ,130,L
	      ,130,L
	      ,,L
	      EOF
       will partition /dev/hdb into two Linux partitions of 3 and 60 cylinders, 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 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.)

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 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 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.

DRDOS WARNINGS
       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.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 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
       moment.'

       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.

BUGS
       There are too many options.

       There is no support for non-DOS partition types.

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

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

Linux					 1 September 1995				SFDISK(8)


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