.TH PREP 8
.SH NAME
prep, fdisk, format, mbr \- prepare hard and floppy diskettes, flashes
.SH SYNOPSIS
.B disk/prep
[
.B -bcfnprw
]
[
.B -a
.I name
]...
[
.B -s
.I sectorsize
]
.I plan9partition
.PP
.B disk/fdisk
[
.B -abfprw
]
[
.B -s
.I sectorsize
]
.I disk
.PP
.B disk/format
[
.B -dfvx
]
[
.B -b
.I bootblock
]
[
.B -c
.I csize
]
[
.B -l
.I label
]
[
.B -r
.I nresrv
]
[
.B -t
.I type
]
.I disk
[
.IR file ...
]
.PP
.B disk/mbr
[
.B -9
]
[
.B -m
.I mbrfile
]
.I disk
.SH 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 master boot record
of the disk.
Partitions of type
.B 0x39
are Plan 9 partitions.
The names of PC partitions are chosen by convention from the type:
.BR dos ,
.BR 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).
.PP
Plan 9 partitions (and Plan 9 disks on non-PCs) are
themselves divided, using a textual partition table, called the Plan 9 partition table, in the second
sector of the partition (the first is left for architecture-specific boot data, such as PC boot blocks).
The table is a sequence of lines of the format
.BI part " name start end" \fR,
where
.I start
and
.I end
name the starting and ending sector.
Sector 0 is the first sector of the Plan 9 partition or disk,
regardless of its position 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.
.PP
The Plan 9 partition often contains a number of
conventionally named subpartitions.
They include:
.TF arenas
.TP
.B 9fat
A small FAT file system used to hold
configuration information
(such as
.B plan9.ini
and
.BR 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
.B -r
option to
.IR format .
.TP
.B arenas
A
.IR venti (8)
arenas partition.
.TP
.B cache
A
.IR cfs (4)
file system cache.
.TP
.B fossil
A
.IR fossil (4)
file system.
.TP
.B fs
A
.IR kfs (4)
file system.
.TP
.B fscfg
A one-sector partition used to store an
.IR fs (3)
configuration.
.TP
.B isect
A
.IR venti (8)
index section.
.TP
.B nvram
A one-sector partition used to simulate non-volatile RAM on PCs.
.TP
.B other
A non-archived
.IR fossil (4)
file system.
.TP
.B swap
A
.IR swap (8)
swap partition.
.PD
.PP
.I Fdisk
edits the PC partition table and is usually
invoked with a disk like
.B /dev/sdC0/data
as its argument, while
.I prep
edits the Plan 9 partition table
and is usually invoked with a disk partition
like
.B /dev/sdC0/plan9
as its argument.
.I Fdisk
works in units of disk ``cylinders'': the cylinder
size in bytes is printed when
.I fdisk
starts.
.I Prep
works in units of disk sectors, which are almost always 512 bytes.
.I Fdisk
and
.I prep
share most of their options:
.TP
.B -a
Automatically partition the disk.
.I 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),
.I fdisk
will mark the new partition active.
.IR Prep 's
.B -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,
.I 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.
.TP
.B -b
Start with a blank disk, ignoring any extant partition table.
.TP
.B -p
Print a sequence of commands that when sent to the disk device's
.B ctl
file
will bring the partition
table information kept by
the
.IR sd (3)
driver up to date.
Then exit.
.I 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
.I fdisk
operates on a table of unnamed partitions,
it assigns names based on the partition type
(e.g.,
.BR plan9 ,
.BR dos ,
.BR ntfs ,
.BR linux ,
.BR linuxswap )
and resolves collisions by appending a numbered suffix.
(e.g.,
.BR dos ,
.BR dos.1 ,
.BR dos.2 ).
.TP
.B -r
In the absence of the
.B -p
and
.B -w
flags,
.I prep
and
.I fdisk
enter an interactive partition editor;
the
.B -r
flag runs the editor in read-only mode.
.TP
.BI -s " sectorsize"
Specify the disk's sector size.
In the absence of this flag,
.I prep
and
.I fdisk
look for a disk
.B ctl
file and read it to find the disk's sector size.
If the
.B ctl
file cannot be found, a message is printed and
a sector size of 512 bytes is assumed.
.TP
.B -w
Write the partition table to the disk and exit.
This is useful when used in conjunction with
.B -a
or
.BR -b .
.PP
If neither the
.B -p
flag nor the
.B -w
flag is given,
.I prep
and
.I 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
.BR p \fIn\fR,
secondary partitions
.BR s \fIn\fR.
The number of primary partitions plus number of contiguous chains of
secondary partitions cannot exceed four.
.PP
The commands are as follows.
In the descriptions, read ``sector'' as ``cylinder'' when using
.IR fdisk .
.TP
.B "a\fR \fIname\fR [ \fIstart\fR [ \fIend\fR ] ]"
Create a partition named
.I name
starting at sector offset
.I start
and ending at offset
.IR end .
The new partition will not be created if
it overlaps an extant partition.
If
.I start
or
.I end
are omitted,
.I prep
and
.I fdisk
will prompt for them.
In
.IR fdisk ,
the newly created partition has type
.RB `` PLAN9 ;''
to set a different type, use the
.B t
command (q.v.).
.I Start
and
.I end
may be expressions using the operators
.BR + ,
.BR - ,
.BR * ,
and
.BR / ,
numeric constants, and the
pseudovariables
.B .
and
.BR $ .
At the start of the program,
.B .
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
.B .
command.
When evaluating
.IR start ,
.B $
is set to one past the last disk sector.
When evaluating
.IR end ,
.B $
is set to the maximum value that
.I end
can take on without running off the disk
or into another partition.
Finally, the expression
.IB n %
evaluates to
.RI ( n × disksize )/100.
As an example,
.B a
.B .
.B .+20%
creates a new partition starting at
.B .
that takes up a fifth of the disk,
and
.B a
.B 1000
.B $
creates a new partition starting at
sector 1000 and
extending as far as possible.
.TP
.B ".\fR \fInewdot"
Set the value of the variable
.B .
to
.IR newdot ,
which is an arithmetic expression as described
in the discussion of the
.B a
command.
.TP
.BI d " name"
Delete the named partition.
.TP
.B h
Print a help message listing command synopses.
.TP
.B 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
.B '
is prefixed to the names of partitions
whose entries have been modified but not written to disk.
.I Fdisk
adds to the end of each line a textual partition type,
and places a
.B *
next to the name of the active partition
(see the
.B A
command below).
.TP
.B P
Print the partition table in the format accepted by the disk's
.B ctl
file, which is also the format of the output of the
.B -p
option.
.TP
.B w
Write the partition table to disk.
.I 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),
.I prep
and
.I fdisk
will attempt to restore the partition table to
its former state.
.TP
.B q
Quit the program.
If the partition table has been modified but not written,
a warning is printed.
Typing
.B q
again will quit the program.
.PP
.I Fdisk
also has the following commands.
.TP
.BI A " name
Set the named partition active.
The active partition is the one whose boot block is used
when booting a PC from disk.
.TP
.B e
Print the names of empty slots in the partition table, i.e., the
valid names to use when creating a new partition.
.TP
.BI t " \fR[\fI type \fR]
Set the partition type.  If it is not given,
.I fdisk
will display a list of choices and then prompt for it.
.PD
.PP
.I Format
prepares for use the floppy diskette or hard disk partition in the file named
.IR disk ,
for example
.B /dev/fd0disk
or
.BR /dev/sdC0/9fat .
The options are:
.TP
.B -f
Do not physically format the disc. Used
to install a FAT file system on a
previously formatted disc. If
.I disk
is not a floppy device, this flag is a no-op.
.TP
.B -t
specify a density and type of disk to be prepared.
The possible
.I types
are:
.RS
.TP
.B 3½DD
3½" double density, 737280 bytes
.TP
.B 3½HD
3½" high density, 1474560 bytes
.TP
.B 5¼DD
5¼" double density, 368640 bytes
.TP
.B 5¼HD
5¼"  high density, 1146880 bytes
.TP
.B hard
fixed disk
.PD
.PP
The default when
.I disk
is a floppy drive is the highest possible on the device.
When
.I disk
is a regular file, the default is
.BR 3½HD .
When
.I disk
is an
.IR sd (3)
device, the default is
.BR hard .
.RE
.TP
.B -d
initialize a FAT file system on the
.IR disk .
.TP
.B -b
use the contents of
.I bootblock
as a bootstrap block
to be installed in sector 0.
.PD
.PP
The remaining options have effect only when
.B -d
is specified:
.TP
.B -c
use a FAT cluster size of
.I csize
sectors when creating the FAT.
.TP
.B -l
add a
.I label
when creating the FAT file system.
.TP
.BI -r
mark the first
.I nresrv
sectors of the partition as ``reserved''.
Since the first sector always contains the
FAT parameter block, this really marks
the
.IR nresrv -1
sectors starting at sector 1 as ``reserved''.
When formatting the
.B 9fat
partition,
.B -r
.B 2
should be used to jump over the partition table sector.
.PD
.PP
Again under
.BR -d ,
any
.I files
listed are added, in order,
to the root
directory of the FAT file system.  The files are
contiguously allocated.
If a file is named
.BR 9load ,
it will be created with the
.B SYSTEM
attribute set so that
.IR dossrv (4)
keeps it contiguous when modifying it.
.PP
.I Format
checks for a number of common mistakes; in particular,
it will refuse to format a
.B 9fat
partition unless
.B -r
is specified with
.I nresrv
larger than two.
It also refuses to format a raw
.IR sd (3)
partition that begins at offset zero in the disk.
(The beginning of the disk should contain an
.I fdisk
partition table with master boot record,
not a FAT file system or boot block.)
Both checks are disabled by the
.B -x
option.
The
.B -v
option prints debugging information.
.PP
The file
.B /386/pbs
is an example of a suitable
.I 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
.BR 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
.B /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.
.PP
.I Mbr
installs a new boot block in sector 0 (the master boot record)
of a disk such as
.BR /dev/sdC0/data .
If
.I mbrfile
contains 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
.IR 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
.IR 9load (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,
.B /386/mbr
is an appropriate
.IR mbrfile .
It detects and uses LBA addressing when available
from the BIOS (the same could not
be done in the case of
.B pbs
due to space considerations).
If the
.I mbrfile
is not specified, a boot block is installed that
prints a message explaining that the disk is not bootable.
The
.B -9
option initialises the partition table to consist of one
.BR plan9
partition which spans the entire disc starting at the end of the
first track.
.SH EXAMPLES
Initialize the kernel disk driver with the partition information
from the FAT boot sectors.
If Plan 9 partitions exist, pass that partition information as well.
.IP
.EX
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
}
.EE
.PP
Create a Plan 9 boot floppy on a previously formatted diskette:
.IP
.EX
disk/format -b /386/pbs -df /dev/fd0disk \e
	/386/9load /tmp/plan9.ini /386/9pcf.gz
.EE
.PP
Initialize the blank hard disk
.BR /dev/sdC0/data .
.IP
.EX
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 \e
	/386/9load /386/9pcf /tmp/plan9.ini
.EE
.PP
Create a bootable USB disk or flash-memory device to be booted
via the BIOS and with no partitions:
.IP
.EX
usb/disk
disk/format -b /386/pbslba -df /n/disk/0/data \e
	/386/9load /386/9pcf.gz /tmp/plan9.ini
.EE
.SH SOURCE
.B /sys/src/cmd/disk/prep
.br
.B /sys/src/boot/pc
.SH SEE ALSO
.IR floppy (3),
.IR sd (3),
.IR 9load (8),
.IR partfs (8)
.SH BUGS
.I 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.