PREP(8)                                                   PREP(8)

     NAME
          prep, edisk, fdisk, format, mbr - prepare disks, floppies
          and flashes

     SYNOPSIS
          disk/prep [ -bcfnprw ] [ -a name ]...  [ -s sectorsize ]
          plan9partition

          disk/edisk [ -abfprw ] [ -s sectorsize ] disk

          disk/fdisk [ -abfprw ] [ -s sectorsize ] disk

          disk/format [ -dfvx ] [ -b bootblock ] [ -c csize ] [ -l
          label ] [ -r nresrv ] [ -t type ] disk [ file... ]

          disk/mbr [ -9 ] [ -m mbrfile ] disk

     DESCRIPTION
          A partition table is stored on a hard disk to specify the
          division of the physical disk into a set of logical units.
          On PCs using traditional DOS partition table, the partition
          entries are stored at the end of the master boot record of
          the disk.  Partitions of type 0x39 are Plan 9 partitions.
          EFI systems use GUID partition table (GPT) format where par-
          tition types are identied by a 128-bit long identifiers. The
          randomly generated GUID C91818F9-8025-47AF-89D2-F030D7000C2C
          is used to identify the Plan 9 partition type in this
          scheme.  The names of DOS and GPT partitions are chosen by
          convention from the type: dos, plan9, etc.  Second and sub-
          sequent partitions of the same type on a given disk are
          given unique names by appending a number (or a period and a
          number if the name already ends in a number).

          Plan 9 partitions (and Plan 9 disks on non-PCs) are them-
          selves divided, using a textual partition table, called the
          Plan 9 partition table, in the second sector of the parti-
          tion (the first is left for architecture-specific boot data,
          such as PC boot blocks).  The table is a sequence of lines
          of the format part name start end, where start and end name
          the starting and ending sector.  Sector 0 is the first sec-
          tor of the Plan 9 partition or disk, regardless of its posi-
          tion in a larger disk.  Partition extents do not contain the
          ending sector, so a partition from 0 to 5 and a partition
          from 5 to 10 do not overlap.

          The Plan 9 partition often contains a number of convention-
          ally named subpartitions.  They include:

          9fat    A small FAT file system used to hold configuration
                  information (such as plan9.ini and plan9.nvr) and

     PREP(8)                                                   PREP(8)

                  kernels.  This typically begins in the first sector
                  of the partition, and contains the partition table
                  as a ``reserved'' sector.  See the discussion of the
                  -r option to format.
          arenas  A venti(8) arenas partition.
          bloom   A venti(8) bloom-filter partition.
          cache   A cfs(4) file system cache.
          fscache A cwfs(4) worm cache partition.
          fsworm  A cwfs(4) worm filesystem.
          fs      A kfs file system.
          fscfg   A one-sector partition used to store an fs(3) con-
                  figuration.
          isect   A venti(8) index section.
          nvram   A one-sector partition used to simulate non-volatile
                  RAM on PCs.
          other   A non-archived cwfs(4) file system.
          swap    A swap(8) swap partition.

          Fdisk edits the DOS partition table and is usually invoked
          with a disk like /dev/sdC0/data as its argument, while prep
          edits the Plan 9 partition table and is usually invoked with
          a disk partition like /dev/sdC0/plan9 as its argument.
          Edisk is similar to fdisk but edits the GPT partition table
          on EFI systems.  Fdisk works in units of disk ``cylinders'':
          the cylinder size in bytes is printed when fdisk starts.
          Prep and edisk works in units of disk sectors, which are
          almost always 512 bytes.  Fdisk, edisk and prep share most
          of their options:

          -a  Automatically partition the disk.  Fdisk and edisk will
              create a Plan 9 partition in the largest unused area on
              the disk, doing nothing if a Plan 9 partition already
              exists.  Edisk also adds a EFI system partition (esp)
              when not already exists.  If no other partition on the
              disk is marked active (i.e. marked as the boot parti-
              tion), fdisk will mark the new partition active.  Prep's
              -a flag takes the name of a partition to create.  (See
              the list above for partition names.)  It can be repeated
              to specify a list of partitions to create.  If the disk
              is currently unpartitioned, prep will create the named
              partitions on the disk, attempting to use the entire
              disk in a sensible manner.  The partition names must be
              from the list given above.

          -b  Start with a blank disk, ignoring any extant partition
              table.

          -p  Print a sequence of commands that when sent to the disk
              device's ctl file will bring the partition table infor-
              mation kept by the sd(3) driver up to date.  Then exit.
              Prep will check to see if it is being called with a disk

     PREP(8)                                                   PREP(8)

              partition (rather than an entire disk) as its argument;
              if so, it will translate the printed sectors by the
              partition's offset within the disk.  Since fdisk and
              edisk operate on a table of unnamed partitions, they
              assign names based on the partition type (e.g., plan9,
              dos, ntfs, linux, linuxswap) and resolve collisions by
              appending a numbered suffix.  (e.g., dos, dos.1, dos.2).

          -r  In the absence of the -p and -w flags, prep, edisk and
              fdisk enter an interactive partition editor; the -r flag
              runs the editor in read-only mode.

          -s sectorsize
              Specify the disk's sector size.  In the absence of this
              flag, prep, edisk and fdisk look for a disk ctl file and
              read it to find the disk's sector size.  If the ctl file
              cannot be found, a message is printed and a sector size
              of 512 bytes is assumed.

          -w  Write the partition table to the disk and exit.  This is
              useful when used in conjunction with -a or -b.

          If neither the -p flag nor the -w flag is given, prep, edisk
          and fdisk enter an interactive partition editor that oper-
          ates on named partitions.  The DOS partition table distin-
          guishes between primary partitions, which can be listed in
          the boot sector at the beginning of the disk, and secondary
          (or extended) partitions, arbitrarily many of which may be
          chained together in place of a primary partition.  Primary
          partitions are named pn, secondary partitions sn.  The num-
          ber of primary partitions plus number of contiguous chains
          of secondary partitions cannot exceed four.  The GPT parti-
          tion table is a fixed array of partition entries (usually
          128). Partitions are named pn, where n indexes the entry in
          array starting from 1 for the first entry.

          The commands are as follows.  In the descriptions, read
          ``sector'' as ``cylinder'' when using fdisk.

          a name [ start [ end ] ]
                    Create a partition named name starting at sector
                    offset start and ending at offset end. The new
                    partition will not be created if it overlaps an
                    extant partition.  If start or end are omitted,
                    the editor will prompt for them.  In fdisk and
                    edisk the newly created partition is of the Plan 9
                    type; to set a different type, use the t command
                    (q.v.).  Start and end may be expressions using
                    the operators +, -, *, and /, numeric constants,
                    and the pseudovariables . and $.  At the start of
                    the program, . is set to zero; each time a

     PREP(8)                                                   PREP(8)

                    partition is created, it is set to the end sector
                    of the new partition.  It can also be explicitly
                    set using the . command.  When evaluating start, $
                    is set to one past the last disk sector.  When
                    evaluating end, $ is set to the maximum value that
                    end can take on without running off the disk or
                    into another partition.  Numeric constants fol-
                    lowed by `k', `m', `g', or `t' (or upper-case
                    equivalents) are scaled to the respective size in
                    kilo-, mega-, giga-, or tera-bytes.  Finally, the
                    expression n% evaluates to (n×disksize)/100.  As
                    examples, `a . .+20%' creates a new partition
                    starting at . that takes up a fifth of the disk,
                    `a . .+21G' creates a new partition starting at .
                    that takes up 21 gigabytes (21×230 bytes), and `a
                    1000 $' creates a new partition starting at sector
                    1000 and extending as far as possible.

          . newdot  Set the value of the variable . to newdot, which
                    is an arithmetic expression as described in the
                    discussion of the a command.

          d name    Delete the named partition.

          h         Print a help message listing command synopses.

          p         Print the disk partition table.  Unpartitioned
                    regions are also listed.  The table consists of a
                    number of lines containing partition name, begin-
                    ning and ending sectors, and total size.  A ' is
                    prefixed to the names of partitions whose entries
                    have been modified but not written to disk.  Fdisk
                    adds to the end of each line a textual partition
                    type, and places a * next to the name of the
                    active partition (see the A command below).

          P         Print the partition table in the format accepted
                    by the disk's ctl file, which is also the format
                    of the output of the -p option.

          w         Write the partition table to disk.  Prep will also
                    inform the kernel of the changed partition table.
                    The write will fail if any programs have any of
                    the disk's partitions open.  If the write fails
                    (for this or any other reason), the program will
                    attempt to restore the partition table to its for-
                    mer state.

          q         Quit the program.  If the partition table has been
                    modified but not written, a warning is printed.
                    Typing q again will quit the program.

     PREP(8)                                                   PREP(8)

          Fdisk also has the following commands.

          A name      Set the named partition active.  The active par-
                      tition is the one whose boot block is used when
                      booting a PC from disk.

          t name [ type ]
                      Set the partition type.  If it is not given,
                      fdisk will display a list of choices and then
                      prompt for it.

          Edisk also has the following commands.

          t name [ type ]
                      Set the partition type; like fdisk above.

          f name [ +-attr ]
                      Set or clear partition attributes.

          l name [ label ]
                      Set the partition label.

          Format prepares for use the floppy diskette or hard disk
          partition in the file named disk, for example /dev/fd0disk
          or /dev/sdC0/9fat.  The options are:

          -f   Do not physically format the disc. Used to install a
               FAT file system on a previously formatted disc. If disk
               is not a floppy device, this flag is a no-op.

          -t   specify a density and type of disk to be prepared.  The
               possible types are:

               3½DD 3½" double density, 737280 bytes

               3½HD 3½" high density, 1474560 bytes

               5¼DD 5¼" double density, 368640 bytes

               5¼HD 5¼"  high density, 1146880 bytes

               hard fixed disk

               The default when disk is a floppy drive is the highest
               possible on the device.  When disk is a regular file,
               the default is 3½HD.  When disk is an sd(3) device, the
               default is hard.

          -d   initialize a FAT file system on the disk.

     PREP(8)                                                   PREP(8)

          -b   use the contents of bootblock as a bootstrap block to
               be installed in sector 0.

          The remaining options have effect only when -d is specified:

          -c   use a FAT cluster size of csize sectors when creating
               the FAT.

          -l   add a label when creating the FAT file system.

          -r   mark the first nresrv sectors of the partition as
               ``reserved''.  Since the first sector always contains
               the FAT parameter block, this really marks the nresrv-1
               sectors starting at sector 1 as ``reserved''.  When
               formatting the 9fat partition, -r 2 should be used to
               jump over the partition table sector.

          Again under -d, any files listed are added, in order, to the
          root directory of the FAT file system.  The files are con-
          tiguously allocated.

          Format checks for a number of common mistakes; in particu-
          lar, it will refuse to format a 9fat partition unless -r is
          specified with nresrv larger than two.  It also refuses to
          format a raw sd(3) partition that begins at offset zero in
          the disk.  (The beginning of the disk should contain an
          fdisk partition table with master boot record, not a FAT
          file system or boot block.)  Both checks are disabled by the
          -x option.  The -v option prints debugging information.

          The file /386/pbs is an example of a suitable bfile to make
          the disk a boot disk.  It gets loaded by the BIOS at 0x7C00,
          reads the first sector of the root directory into address
          0x7E00, and looks for a directory entry named 9BOOTFAT.  If
          it finds such an entry, it uses single sector reads to load
          the file into address 0x7C00 and then jumps to the loaded
          file image.

          Mbr installs a new boot block in sector 0 (the master boot
          record) of a disk such as /dev/sdC0/data.  If mbrfile con-
          tains more than one sector of `boot block', the rest will be
          copied into the first track of the disk, if it fits.  This
          boot block should not be confused with the boot block used
          by format, which goes in sector 0 of a partition.  Typi-
          cally, the boot block in the master boot record scans the PC
          partition table to find an active partition and then exe-
          cutes the boot block for that partition.  The partition boot
          block then loads a bootstrap program such as 9boot(8), which
          then loads the operating system.  If MS-DOS or Windows 9[58]
          is already installed on your hard disk, the master boot
          record already has a suitable boot block.  Otherwise,
          /386/mbr is an appropriate mbrfile. It detects and uses LBA

     PREP(8)                                                   PREP(8)

          addressing when available from the BIOS (the same could not
          be done in the case of pbs due to space considerations).  If
          the mbrfile is not specified, a boot block is installed that
          prints a message explaining that the disk is not bootable.
          The -9 option initialises the partition table to consist of
          one plan9 partition which spans the entire disc starting at
          the end of the first track.

     EXAMPLES
          Initialize the kernel disk driver with the partition infor-
          mation from the FAT boot sectors.  If Plan 9 partitions
          exist, pass that partition information as well.

               for(disk in /dev/sd??) {
                    if(test -f $disk/data && test -f $disk/ctl)
                         disk/fdisk -p $disk/data >$disk/ctl
                    for(part in $disk/plan9*)
                         if(test -f $part)
                              disk/prep -p $part >$disk/ctl
               }

          Initialize the blank hard disk /dev/sdC0/data.

               disk/mbr -m /386/mbr /dev/sdC0/data
               disk/fdisk -baw /dev/sdC0/data
               disk/prep -bw -a^(9fat nvram fscache fsworm other swap) /dev/sdC0/plan9
               disk/format -b /386/pbs -d -r 2 /dev/sdC0/9fat \
                    /386/9bootfat /386/9pcf /tmp/plan9.ini

     FILES
          /386/mbr

          /386/pbs

     SOURCE
          /sys/src/cmd/disk/prep
          /sys/src/boot/pc

     SEE ALSO
          floppy(3), sd(3), nusb(4), 9boot(8), partfs(8), diskparts(8)

     BUGS
          If `prep -p' doesn't find a Plan 9 partition table, it will
          emit commands to delete all extant partitions.  Similarly,
          `fdisk -p' will delete all partitions, including `data', if
          there are no partitions defined in the MBR.