prep, edisk, fdisk, format, mbr – prepare disks, floppies and flashes|
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
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
(GPT) format where partition 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 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:
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:
–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 sectors by
If neither the –p flag nor the –w flag is given, prep, edisk and fdisk enter an interactive partition editor that operates on named partitions. The DOS 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 number of primary partitions plus number of contiguous chains of secondary partitions cannot exceed four. The GPT partition 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.
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
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 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.
t name [ type ]
–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:
–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:
Again under –d, any files listed are added, in order, to the root directory of the FAT file system. The files are contiguously allocated.
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 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 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. 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 9boot(8), which
then loads the operating system. If MS–DOS or Windows
9 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 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.
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.|
floppy(3), sd(3), nusb(4), 9boot(8), partfs(8), diskparts(8)|
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.|