Yolinux.com

sfdisk manpage

Search topic Section
Get manual page for the search topic
List all commands matching the search topic
List all topics in the manpage index

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 partitions. 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 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 par-
       titions 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  val-
       ues, ask for a listing with sectors as unit.


   Check partitions
       The  third type of invocation: sfdisk -V device will apply various con-
       sistency 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 stan-
       dard input, and then to change the partition tables on that disk. Thus,
       it  is  possible	 to use sfdisk from a shell script. When sfdisk deter-
       mines 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 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
	      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  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 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	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 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
       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
       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)



Linux			       1 September 1995			     SFDISK(8)
YoLinux.com Home Page
YoLinux Tutorial Index
Privacy Policy | Advertise with us | Feedback Form |
Unauthorized copying or redistribution prohibited.
    Bookmark and Share