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    Command:

    sfdisk

    
    
    

    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 partitions. In particular case use more advanced GNU
           parted(8).
    
           Note  that sfdisk does not align partitions to block device I/O limits.
           This functionality is provided by fdisk(8).
    
       List Sizes
           sfdisk -s partition gives the size of partition in blocks. This may  be
           useful in connection 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
           block devices, 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 par-
           titions on all hard block devices 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 specification for the desired partitioning of device from its stan-
           dard  input,  and  then  to  change  the partition tables on that block
           device. 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 block device, 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 block device 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 block
                  device(s)
    
           -G or --show-pt-geometry
                  List the geometry of the  indicated  block  devices  guessed  by
                  looking at the partition table.
    
           -l or --list
                  List the partitions of a device.
    
           -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 ker-
                  nel thinks.
    
           -f or --force
                  Do what I say, even if it is stupid.
    
           -q or --quiet
                  Suppress warning messages.
    
    
           -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 block device.)
    
           --IBM or --leave-last
                  Certain IBM diagnostic programs assume that  they  can  use  the
                  last  cylinder  on  a block device 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  block
                  device.
    
           -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 block device, sfdisk  checks
                  that this device 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 block device, 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 block device (the Master Boot Record) contains among other
           things  four  partition  descriptors. The partitions described here are
           24 bits are available, which does not suffice  for  big  block  devices
           (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 prob-
           lems 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
           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  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  block  device  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).
    
                  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  cylin-
           ders,  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 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/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 block
           device useless.
           partition.   Mind  you,  as  long  as I keep a little free device 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 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 hex-
           adecimal 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

           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-ng package and is avail-
           able from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
    
    
    

    Linux 1 September 1995 SFDISK(8)

    
    
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