PREP(8) PREP(8)
NAME
prep, fdisk, format, mbr - prepare hard and floppy
diskettes, flashes
SYNOPSIS
disk/prep [ -abcfnprw ] [ -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 [ -m mbrfile ]
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, the partition table is stored at the end of the mas-
ter boot record of the disk. Partitions of type 0x39 are
Plan 9 partitions. The names of PC 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
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.
cache A cfs(4) file system cache.
fs A kfs(4) file system.
swap A swap(8) swap partition.
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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 will create 9fat,
swap, and fs partitions, doing nothing if the disk has
already been partitioned. If the -c option is present,
prep will also create a cache partition. If the -n
option is present, prep will create a one-sector nvram
partition.
-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
operates 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
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
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 and
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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. 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 partition is created, it
is set to the end sector of the new partition. It can
also be explicitly set using the . command. When eval-
uating start, $ is set to one past the last disk sec-
tor. When evaluating end, $ is set to the maximum
value that end can take on without running off the disk
or into another partition. Finally, the expression n%
evaluates to (n×disksize)/100. As an example, a .
.+20% creates a new partition starting at . that takes
up a fifth of the disk, and a 1000 $ creates a new par-
tition 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, beginning 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).
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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 mod-
ified 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 partition
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 creating a new parti-
tion.
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 filesystem 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 a n sd(3) device,
the default is hard.
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-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 filesystem. 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)
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 bfile to make
the disk a boot disk. It gets loaded by the BIOS at 0x7C00,
reads the root directory into address 0x7E00, and looks at
the first root directory entry. If that file is called
9LOAD, 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 all BIOSes), it can access more
than the first 8.5GB of the disk.
Mbr installs a new boot block in sector 0 (the master boot
record) of a disk such as /dev/sdC0/data. This boot block
should not be confused with the boot block used by format,
which goes in sector 0 of a partition. Typically, the boot
block in the master boot record scans the PC partition table
to find an active partition and then executes the boot block
for that partition. The partition boot block then loads a
bootstrap program such as 9load(8), which then loads the
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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 appro-
priate 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 mes-
sage explaining that the disk is not bootable.
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
}
Create a Plan 9 boot floppy on a previously formatted
diskette:
disk/format -b /386/pbs -df /dev/fd0disk /386/9load /tmp/plan9.ini
Initialize the blank hard disk /dev/sdC0/data.
disk/mbr -m /386/mbr /dev/sdC0/data
disk/fdisk -baw /dev/sdC0/data
disk/prep -baw /dev/sdC0/plan9
disk/format -b /386/pbs -d -r 2 /dev/sdC0/9fat 9load 9pcdisk plan9.ini
SOURCE
/sys/src/cmd/disk/prep
/sys/src/boot/pc
SEE ALSO
floppy(3), sd(3), 9load(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.
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