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

NAME
       sfdisk -	Partition table	manipulator for	Linux

SYNOPSIS
       sfdisk-linux [options] device
       sfdisk-linux -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.

   List	Sizes
       sfdisk-linux  -s	 partition gives the size of partition in blocks. This
       may be useful in	connection with	programs like mkswap or	so. Here  par-
       tition  is  usually  something  like /dev/ad0s1 or /dev/da2s12, but may
       also be an entire disk, like /dev/amrd0.
	      %	sfdisk-linux -s	/dev/ad0s9
	      81599
	      %
       If the partition	argument is omitted, sfdisk will list the sizes	of all
       disks, and the total:
	      %	sfdisk-linux -s
	      /dev/ad0:	208896
	      /dev/ad1:	1025136
	      /dev/ad2:	1031063
	      /dev/da0:	8877895
	      /dev/da1:	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 par-
       titions on all hard disks are listed.
       % sfdisk-linux -l /dev/ad2

       Disk /dev/ad2: 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/ad2s1	   0+	 406	 407-	205096+	 83  Linux native
       /dev/ad2s2	 407	 813	 407	205128	 83  Linux native
       /dev/ad2s3	 814	2044	1231	620424	 83  Linux native
       /dev/ad2s4	   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  val-
       ues, ask	for a listing with sectors as unit.

   Check partitions
       The third type of invocation: sfdisk-linux -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-linux -V -q device  which  only  returns  a
       status.

   Create partitions
       The fourth type of invocation: sfdisk-linux 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 de-
       termines	 that  its  standard input is a	terminal, it will be conversa-
       tional; 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-linux /dev/ad3 -O ad3-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-linux /dev/ad3 -I ad3-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.

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-linux -d /dev/ad0 > ad0.out
		  % sfdisk-linux /dev/ad0 < ad0.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-linux /dev/ad1 -N5
		  ,,,*
		  %
	      will  make  the  fifth partition on /dev/ad1 bootable (`active')
	      and change nothing  else.	 (Probably  this  fifth	 partition  is
	      called  /dev/ad1s5,  but you are free to call it something else,
	      like `/my_equipment/disks/2/5' or	so).

       -Anumber
	      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-linux --print-id /dev/ad1 5
		  6
		  % sfdisk-linux --change-id /dev/ad1 5	83
		  OK
	      first  reports  that  /dev/ad1s5 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 ker-
	      nel 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 cannot contain sector 0, e.g. because that	is the
	      MBR of the device, or contains the partition  table  of  an  ex-
	      tended  partition, then sfdisk would make	it start the next sec-
	      tor. 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.	Sometimes  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 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.

       --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 re-
	      fuses 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.)

       -O file
	      Just before writing the new partition, output the	 sectors  that
	      are  going  to  be overwritten to	file (where hopefully file re-
	      sides 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 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  de-
       tails, see the lilo documentation.

       Each  partition	has a type, its	`Id', and if this type is 5 or f (`ex-
       tended 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  ex-
       tended  partition (or empty).  In this way one gets a chain of extended
       partitions.  Other operating systems have  slightly  different  conven-
       tions.	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  sys-
       tems.)

       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.

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 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 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 EX-
       TENDED_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 de-
       faults 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.

EXAMPLE
       The command
	      sfdisk-linux /dev/ad2 << EOF
	      0,407
	      ,407
	      ;
	      ;
	      EOF
       will partition /dev/ad2 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	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.)

DOS 6.x	WARNING
       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/ad0s1, 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/ad0s1 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  example,	 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  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 re-
       ported to have difficulties with	partition ID codes of 80 or more.  The
       Linux `fdisk' used to set the system type of new	partitions to hexadec-
       imal 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 prob-
       lems 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 it-
       self seems to use the full byte.	I have not been	able to	reproduce  any
       corruption with DRDOS or	its fdisk.

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

       There are too many options.

       There is	no support for non-DOS partition types.

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

SEE ALSO
       cfdisk-linux(8),	fdisk-linux(8),	fdisk(8), newfs(8)

Linux			       1 September 1995			     SFDISK(8)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | THEORY | INPUT FORMAT | EXAMPLE | DOS 6.x WARNING | DRDOS WARNINGS | BUGS | AUTHOR | SEE ALSO

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