= prep, fdisk, format, mbr: prepare hard and floppy diskettes, 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_ ]  A partition table is stored on a hard disk to specify the division ofthe physical disk into a set of logical units. On PCs, the partitiontable is stored at the end of the master boot record of the disk.Partitions of type *0x39* are Plan 9 partitions. Inferno uses the sametype and follows other Plan 9 conventions described here. The names ofPC partitions are chosen by convention from the type: *dos*, *plan9*,etc. Second and subsequent partitions of the same type on a given diskare given unique names by appending a number (or a period and a numberif 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, inthe second sector of the partition (the first is left forarchitecture-specific boot data, such as PC boot blocks). Inferno againuses the same conventions. The table is a sequence of lines of theformat **part**__ name start end__*,* where _start_ and _end_ name thestarting and ending sector. Sector 0 is the first sector of the Plan 9partition or disk, regardless of its position in a larger disk.Partition extents do not contain the ending sector, so a partition from0 to 5 and a partition from 5 to 10 do not overlap. The Plan 9 partition often contains a number of conventionally namedsubpartitions. Only *9fat*, *fs* and *nvram* are currently used byInferno, but the others are included for reference. 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 Plan 9 _venti_ arenas partition.*cache*::  A Plan 9 _cfs_ file system cache.*fossil*::  A Plan 9 _fossil_ file system.*fs*::  A _kfs_(4) file system.*fscfg*::  A one-sector partition used to store a _ds_(3) configuration.*isect*::  A Plan 9 _venti_ index section.*nvram*::  A one-sector partition used to simulate non-volatile RAM on PCs.*other*::  A non-archived Plan 9 _fossil_ file system.*swap*::  A Plan 9 swap partition. _Fdisk_ edits the PC partition table and is usually invoked with a disklike */dev/sdC0/data* as its argument, while _prep_ edits the Plan 9partition table and is usually invoked with a disk partition like*/dev/sdC0/plan9* as its argument. _Fdisk_ works in units of disk``cylinders'': the cylinder size in bytes is printed when _fdisk_starts. _Prep_ works in units of disk sectors, which are almost always512 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 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*, *dos1*,  *dos2*).*-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, whichcan be listed in the boot sector at the beginning of the disk, andsecondary (or extended) partitions, arbitrarily many of which may bechained together in place of a primary partition. Primary partitions arenamed **p**__n__, secondary partitions **s**__n__. The number of primarypartitions plus number of contiguous chains of secondary partitionscannot 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 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_, *$* is set to the maximum value that  _end_ can take on without running off the disk or into another  partition. Finally, the expression __n__**%** evaluates to  (__n__×_disksize_)/100. As an example, *a* *.* *.+20%* creates a new  partition starting at *.* that takes up a fifth of the disk, and *a*  *1000* *$* 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. **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_ prepares for use the floppy diskette or hard disk partition inthe 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 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 rootdirectory 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 willrefuse 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 thedisk 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 */Inferno/386/pbs* is an example of a suitable _bfile_ to makethe disk a boot disk. It gets loaded by the BIOS at 0x7C00, reads theroot directory into address 0x7E00, and looks at the first rootdirectory entry. If that file is called *9LOAD*, it uses single sectorreads to load the file into address 0x10000 and then jumps to the loadedfile image. The file */Inferno/386/pbslba* is similar, but because ituses LBA addressing (not supported by all BIOSes), it can access morethan the first 8.5GB of the disk. _Mbr_ installs a new boot block in sector 0 (the master boot record) ofa disk such as */dev/sdC0/data*. This boot block should not be confusedwith the boot block used by _format_, which goes in sector 0 of apartition. Typically, the boot block in the master boot record scans thePC partition table to find an active partition and then executes theboot block for that partition. The partition boot block then loads abootstrap program such as _9load_(10.8), which then loads the operatingsystem. If MS-DOS or Windows 9[58] is already installed on your harddisk, the master boot record already has a suitable boot block.Otherwise, */Inferno/386/mbr* is an appropriate _mbrfile_. It detectsand uses LBA addressing when available from the BIOS (the same could notbe done in the case of *pbs* due to space considerations). If the_mbrfile_ is not specified, a boot block is installed that prints amessage explaining that the disk is not bootable. The *-9* optioninitialises the partition table to consist of one *plan9* partitionwhich spans the entire disc starting at the end of the first track. == EXAMPLES Initialize the kernel disk driver with the partition information fromthe FAT boot sectors. If Plan 9 partitions exist, pass that partitioninformation as well. ....for(disk in /dev/sd??) {	if(ftest -f $disk/data && ftest -f $disk/ctl){		disk/fdisk -p $disk/data >$disk/ctl	}	for(part in $disk/plan9*){		if(ftest -f $part){			disk/prep -p $part >$disk/ctl		}	}}.... Create a boot floppy on a previously formatted diskette: ....disk/format -b /Inferno/386/pbs -df /dev/fd0disk /Inferno/386/9load /tmp/plan9.ini.... Initialize the blank hard disk */dev/sdC0/data*. ....disk/mbr -m /Inferno/386/mbr /dev/sdC0/datadisk/fdisk -baw /dev/sdC0/datadisk/prep -bw -a^(9fat fs) /dev/sdC0/plan9disk/format -b /Inferno/386/pbslba -d -r 2 /dev/sdC0/9fat 9load 9pcdisk plan9.ini.... == SOURCE */appl/cmd/disk/prep* +*/appl/cmd/disk/format.b* +*/os/boot/pc* == SEE ALSO _floppy_(3), _sd_(3), _9load_(10.8), _plan9.ini_(10.8) == BUGS _Format_ can create FAT12 and FAT16 file systems, but not FAT32 filesystems. The boot block can only read from FAT12 and FAT16 file systems.