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.

   List Sizes
       sfdisk -s partition gives the size of partition in blocks. This may be useful in connection with programs like mkswap 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 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 -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).

       -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 --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 geom-
	      etry 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 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 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 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.)

       -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 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 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 con-
       ventions.  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.

EXAMPLE

       The command
	      sfdisk /dev/hdc << EOF
	      0,407
	      ,407
	      ;
	      ;
	      EOF
       will partition /dev/hdc 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 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 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 corruption 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  immedi-
       ately  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.esfdisk: `Dr. DOS 5.0 and 6.0 has been reported to have problems cooperating with Linux, and with this ver-
       sion of efdisk in particular.  This efdisk sets the system type to hexadecimal 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  hexadeci-
       mal 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.

BUGS

       A corresponding interactive cfdisk (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(8), fdisk(8), mkfs(8), parted(8)

Linux 1.3.23							 1 September 1995							 SFDISK(8)