term% cat index.txt PREP(8) System Manager's Manual PREP(8)
NAME
prep, 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 tradi‐
tional 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 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:
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.
fscache
A cwfs(4) worm cache partition.
fsworm A cwfs(4) worm filesystem.
fs A kfs(4) file system.
fscfg A one-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 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 parti‐
tion 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
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 partition names.) It can be repeated to specify a
list of partitions to create. If the disk is currently unparti‐
tioned, prep will create the named partitions on the disk, at‐
tempting to use the entire disk in a sensible manner. The par‐
tition 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 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 en‐
ter 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 operates on named parti‐
tions. The DOS partition table distinguishes between primary parti‐
tions, 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 par‐
titions 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 parti‐
tion 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 omit‐
ted, the editor will prompt for them. In fdisk and edisk the
newly created partition is of the Plan 9 type; to set a differ‐
ent type, use the t command (q.v.). Start and end may be ex‐
pressions 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 explic‐
itly 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 ex‐
pression n% evaluates to (nÃdisksize)/100. As examples, creates
a new partition starting at . that takes up a fifth of the
disk, creates a new partition starting at . that takes up 21
gigabytes (21Ã230 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 op‐
tion.
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 at‐
tempt 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.
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.
-b use the contents of bootblock as a bootstrap block to be in‐
stalled 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 di‐
rectory 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 sec‐
tor of the root directory into address 0x7E00, and looks for a direc‐
tory 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. 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 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 addressing when avail‐
able 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
}
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 /386/9pcf /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)
BUGS
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)