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
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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
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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
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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 (21×28309 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.
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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.
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-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
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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 /386/9pc /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.
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