Provided by: util-linux_2.12r-4ubuntu6_i386 bug

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).

       -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).

       -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 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 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
       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.

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  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
       overrunning 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 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  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.

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.

SEE ALSO

       cfdisk(8), fdisk(8), mkfs(8), parted(8)