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
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: .TF arenas
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.
-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 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 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 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 , linuxswap ) 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 secondary (or extended) partitions, arbitrarily many of which may be chained together in place of a primary partition. Primary partitions are named p n, secondary partitions s n. The number of primary partitions 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 . .TF ". newdot
"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, 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 .LR k , .LR m , .LR g , or .LR 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, .L "a . .+20%" creates a new partition starting at . that takes up a fifth of the disk, .L "a . .+21G" creates a new partition starting at . that takes up 21 gigabytes (21×2\u\s-130\s0\d bytes), and .L "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, 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. .TF "t [ type ]
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.
-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 allocated. 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.
Create a Plan 9 boot floppy on a previously formatted diskette.
.EX disk/format -b /386/pbs -df /dev/fd0disk \e /386/9load /tmp/plan9.ini /386/9pcf.gzInitialize the blank disk /dev/sdC0/data .
.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/386/mbr
/386/mbr.bootmgr self-configuring `smart boot manager'
/n/sources/extra/bootmgr.tgz nasm assembler source for /386/mbr.bootmgr
If .L "prep -p" doesn't find a Plan 9 partition table, it will emit commands to delete all extant partitions. Similarly, .L "fdisk -p" will delete all partitions, including .LR data , if there are no partitions defined in the MBR.