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 divi‐
sion 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 chosen 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 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 part name start end, where start and 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.
The Plan 9 partition often contains a number of conventionally 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.
fossil A fossil(4) file system.
fs A kfs(4) file system.
fscfg A few-sector partition used to store an fs(3) configuration.
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 parti‐
tion table and is usually invoked with a disk partition like
/dev/sdC0/plan9 as its argument. Fdisk works in units of disk ``cylin‐
ders'': 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 par‐
tition names.) It can be repeated to specify a list of parti‐
tions 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 information 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 sec‐
tors 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, lin‐
uxswap) 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 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 sec‐
ondary (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 number of primary parti‐
tions 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 omit‐
ted, 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 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 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 or (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, creates a new par‐
tition starting at . that takes up a fifth of the disk, creates
a new partition starting at . that takes up 21 gigabytes
(21×230 bytes), and 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 arith‐
metic expression as described in the discussion of the a com‐
mand.
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 par‐
tition 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).
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 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 partition.
t [ type ]
Set the partition type. If it is not given, fdisk will display
a list of choices and then 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 contiguously allo‐
cated. 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 particular, 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 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 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 executes the boot block for
that partition. The partition boot block then loads a bootstrap pro‐
gram such as 9load (see 9boot(8)), which then loads the operating sys‐
tem. If MS-DOS or Windows is already installed on your disk, the mas‐
ter 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 information 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 /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 ALSOfloppy(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 sys‐
tems. The boot block can only read from FAT12 and FAT16 file systems.
If doesn't find a Plan 9 partition table, it will emit commands to
delete all extant partitions. Similarly, will delete all partitions,
including if there are no partitions defined in the MBR.
PREP(8)
