PREP(8)                                                   PREP(8)

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

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

          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 non-floppy disk to specify
          the division of the physical disk into a set of logical
          units.  On PCs, the partition table is stored at the end of
          the master boot record of the disk.  Partitions of type 0x39
          are Plan 9 partitions.  The names of PC partitions are cho-
          sen by convention from the type: dos, plan9, etc.  Second
          and subsequent 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
                  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.

     PREP(8)                                                   PREP(8)

          fossil  A fossil(4) file system.
          fs      A kfs(4) file system.
          fscfg   A few-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 fossil(4) file system.
          swap    A swap(8) swap partition.

        fdisk and prep
          Fdisk edits the PC 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.
          Fdisk works in units of disk ``cylinders'': the cylinder
          size in bytes is printed when fdisk starts.  Prep works in
          units of disk sectors, which are almost always 512 bytes.
          Fdisk and prep share most of their options:

          -a  Automatically partition the disk.  Fdisk will create a
              Plan 9 partition in the largest unused area on the disk,
              doing nothing if a Plan 9 partition already exists.  If
              no other partition on the disk is marked active (i.e.
              marked as the boot partition), 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 parti-
              tions to create.  If the disk is currently unparti-
              tioned, 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
              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 oper-
              ates on a table of unnamed partitions, it assigns names
              based on the partition type (e.g., plan9, dos, ntfs,
              linux, linuxswap) and resolves collisions by appending a
              numbered suffix.  (e.g., dos, dos.1, dos.2).

          -r  In the absence of the -p and -w flags, prep and fdisk
              enter an interactive partition editor; the -r flag runs

     PREP(8)                                                   PREP(8)

              the editor in read-only mode.

          -s sectorsize
              Specify the disk's sector size.  In the absence of this
              flag, prep and fdisk look for a disk ctl file and read
              it to find the disk's sector size.  If the ctl file can-
              not 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 and
          fdisk enter an interactive partition editor that operates on
          named partitions.  The PC partition table distinguishes
          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 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,
                    prep and fdisk will prompt for them.  In fdisk,
                    the newly created partition has type ``PLAN9;'' to
                    set a different type, use the t command (q.v.).
                    Start and end may be expressions using the opera-
                    tors +, -, *, and /, numeric constants, and the
                    pseudovariables . and $.  At the start of the pro-
                    gram, . is set to zero; each time a 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 followed 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

     PREP(8)                                                   PREP(8)

                    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 extend-
                    ing 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), prep and fdisk
                    will attempt to restore the partition table to its
                    former 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.

          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.

          e           Print the names of empty slots in the partition
                      table, i.e., the valid names to use when creat-
                      ing a new partition.

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

     PREP(8)                                                   PREP(8)

                      prompt for it.

        format and pbs
          Format prepares for use the disk partition or the floppy
          diskette in the file named disk, for example /dev/sdC0/9fat
          or /dev/fd0disk.  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.

          -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.  If a file is named 9load, it will be
          created with the SYSTEM attribute set so that dossrv(4)

     PREP(8)                                                   PREP(8)

          keeps it contiguous when modifying it.

          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 bootblock 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 9LOAD.
          If it finds such an entry, it uses single sector reads to
          load the file into address 0x10000 and then jumps to the
          loaded file image.  The file /386/pbslba is similar, but
          because it uses LBA addressing (not supported by older
          BIOSes), it can access more than the first 8.5GB of the
          disk.  /386/pbsraw is suitable for CDs.

        mbr
          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 9load (see
          9boot(8)), which then loads the operating system.  If MS-DOS
          or Windows is already installed on your disk, the master
          boot record already has a suitable boot block.  Otherwise,
          /386/mbr is an appropriate mbrfile. It detects and uses LBA
          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)

     PREP(8)                                                   PREP(8)

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

          Create a Plan 9 boot floppy on a previously formatted
          diskette.

               disk/format -b /386/pbs -df /dev/fd0disk \
                    /386/9load /tmp/plan9.ini /386/9pcf.gz

          Initialize the blank disk /dev/sdC0/data.

               disk/mbr -m /386/mbr /dev/sdC0/data
               disk/fdisk -baw /dev/sdC0/data
               disk/prep -bw -a^(9fat nvram fossil cache swap) /dev/sdC0/plan9
               disk/format -b /386/pbslba -d -r 2 /dev/sdC0/9fat \
                    /386/9load /386/9pcf /tmp/plan9.ini

     FILES
          /386/mbr
          /386/mbr.bootmgr  self-configuring `smart boot manager'

     SOURCE
          /sys/src/cmd/disk/prep
          /sys/src/boot/pc
          /n/sources/extra/bootmgr.tgz  nasm assembler source for
                                        /386/mbr.bootmgr

     SEE ALSO
          floppy(3), sd(3), usb(4), 9boot(8), mk9660(8), mkusbboot(8),
          partfs(8)

     BUGS
          Format can create FAT12 and FAT16 file systems, but not
          FAT32 file systems.  The boot block can only read from FAT12
          and FAT16 file systems.

          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.