.\" $FreeBSD$ .\" .Dd February 26, 2006 .Dt FDISK 8 .Os .Sh NAME .Nm fdisk .Nd NEC PC-98x1 partition table maintenance program .Sh SYNOPSIS .Nm .Op Fl BIaistuv .Op Fl b Ar bootcode .Op Fl 1234 .Op Ar disk .Nm .Fl f Ar configfile .Op Fl itv .Op Ar disk .Sh PROLOGUE In order for the BIOS to boot the kernel, certain conventions must be adhered to. Sector 0 of the disk must contain boot code, a partition table, and a magic number. BIOS partitions can be used to break the disk up into several pieces. The BIOS brings in sector 0 and verifies the magic number. The sector 0 boot code then searches the partition table to determine which partition is marked .Em active . This boot code then brings in the bootstrap from the .Em active partition and, if marked bootable, runs it. Under DOS, you can have one or more partitions with one .Em active . The DOS .Nm utility can be used to divide space on the disk into partitions and set one .Em active . .Sh DESCRIPTION The .Fx .Nm utility serves a similar purpose to the DOS program. The first form is used to display partition information or to interactively edit the partition table. The second is used to write a partition table using a .Ar configfile and is designed to be used by other scripts/programs. .Pp Options are: .Bl -tag -width time .It Fl a Change the active partition only. Ignored if .Fl f is given. .It Fl b Ar bootcode Get the boot code from the file .Ar bootcode . .It Fl B Reinitialize the boot code contained in sector 0 of the disk. Ignored if .Fl f is given. .It Fl I Initialize the partition table. One .Fx slice covering the entire disk will be created. Some space at the start of the disk will reserved for the IPL program and the pc98 partition table itself. .It Fl f Ar configfile Set partition values using the file .Ar configfile . The .Ar configfile always modifies existing partitions, unless .Fl i is also given, in which case all existing partitions are deleted (marked as "unused") before the .Ar configfile is read. The .Ar configfile can be "-", in which case .Ar stdin is read. See .Sx CONFIGURATION FILE , below, for file syntax. .Pp .Em WARNING : when .Fl f is used, you are not asked if you really want to write the partition table (as you are in the interactive mode). Use with caution! .It Fl i Initialize sector 0 of the disk. This implies .Fl u , unless .Fl f is given. .It Fl s Print summary information and exit. .It Fl t Test mode; do not write partition values. Generally used with the .Fl f option to see what would be written to the partition table. Implies .Fl v . .It Fl u Is used for updating (editing) sector 0 of the disk. Ignored if .Fl f is given. .It Fl v Be verbose. Partitions that are unused are suppressed unless this flag is specified. When .Fl f is used, .Nm prints out the partition table that is written to the disk. .It Fl 12345678 Operate on a single fdisk entry only. Ignored if .Fl f is given. .El .Pp The final disk name can be provided as a .Sq bare disk name only, e.g.\& .Ql da0 , or as a fully qualified device node under .Pa /dev . If omitted, the disks .Ql wd0 , .Ql da0 , and .Ql od0 are being searched in that order, until one is being found responding. .Pp When called with no arguments, it prints the sector 0 partition table. An example follows: .Bd -literal ******* Working on device /dev/rda0 ******* parameters extracted from in-core disklabel are: cylinders=33075 heads=8 sectors/track=32 (256 blks/cyl) parameters to be used for BIOS calculations are: cylinders=33075 heads=8 sectors/track=32 (256 blks/cyl) Media sector size is 512 Warning: BIOS sector numbering starts with sector 1 Information from DOS bootblock is: The data for partition 1 is: sysmid 148,(FreeBSD/NetBSD/386BSD) start 256, size 2490112 (1215 Meg), sid 196 beg: cyl 1/ sector 0/ head 0; end: cyl 9727/ sector 0/ head 0 system Name FreeBSD(98) The data for partition 2 is: sysmid 148,(FreeBSD/NetBSD/386BSD) start 2490368, size 5505024 (2688 Meg), sid 196 beg: cyl 9728/ sector 0/ head 0; end: cyl 31231/ sector 0/ head 0 system Name FreeBSD(98) The data for partition 3 is: The data for partition 4 is: The data for partition 5 is: The data for partition 6 is: The data for partition 7 is: The data for partition 8 is: The data for partition 9 is: The data for partition 10 is: The data for partition 11 is: The data for partition 12 is: The data for partition 13 is: The data for partition 14 is: The data for partition 15 is: The data for partition 16 is: .Ed .Pp The disk is divided into three partitions that happen to fill the disk. The second partition overlaps the end of the first. (Used for debugging purposes) .Bl -tag -width "cyl, sector and head" .It Em "sysmid" is used to label the partition. .Fx reserves the magic number 148 decimal (94 in hex). .It Em start No and Em size fields provide the start address and size of a partition in sectors. .\" !PC98 .It Em "flag 80" .\" specifies that this is the active partition. .It Em cyl , sector No and Em head fields are used to specify the beginning address and end address for the partition. .It Em "system Name" is the name of the partition. .It Em Note : these numbers are calculated using BIOS's understanding of the disk geometry and saved in the bootblock. .El .Pp The flags .Fl i or .Fl u are used to indicate that the partition data is to be updated, unless the .Fl f option is used. If the .Fl f option is not used, the .Nm utility will enter a conversational mode. This mode is designed not to change any data unless you explicitly tell it to. The .Nm utility selects defaults for its questions to guarantee the above behavior. .Pp It displays each partition and ask if you want to edit it. If you say yes, it will step through each field showing the old value and asking for a new one. When you are done with a partition, .Nm will display it and ask if it is correct. The .Nm utility will then proceed to the next entry. .Pp Getting the .Em cyl , sector , and .Em head fields correct is tricky. So by default, they will be calculated for you; you can specify them if you choose. .Pp After all the partitions are processed, you are given the option to change the .Em active partition. Finally, when the all the data for the first sector has been accumulated, you are asked if you really want to rewrite sector 0. Only if you answer yes, will the data be written to disk. .Pp The difference between the .Fl u flag and .Fl i flag is that the .Fl u flag just edits the fields as they appear on the disk. While the .Fl i flag is used to "initialize" sector 0; it will setup the last BIOS partition to use the whole disk for .Fx ; and make it active. .Sh NOTES The automatic calculation of starting cylinder etc.\& uses a set of figures that represent what the BIOS thinks is the geometry of the drive. These figures are by default taken from the incore disklabel, but the program initially gives you an opportunity to change them. This allows the user to create a bootblock that can work with drives that use geometry translation under the BIOS. .Pp If you hand craft your disk layout, please make sure that the .Fx partition starts on a cylinder boundary. A number of decisions made later may assume this. (This might not be necessary later.) .Pp Editing an existing partition will most likely cause you to lose all the data in that partition. .Pp You should run this program interactively once or twice to see how it works. This is completely safe as long as you answer the last question in the negative. There are subtleties that the program detects that are not fully explained in this manual page. .Sh CONFIGURATION FILE When the .Fl f option is given, a disk's partition table can be written using values from a .Ar configfile . The syntax of this file is very simple. Each line is either a comment or a specification, and whitespace (except for newlines) are ignored: .Bl -tag -width Ds .It Xo .Ic # .Ar comment ... .Xc Lines beginning with a "#" are comments and are ignored. .It Xo .Ic g .Ar spec1 .Ar spec2 .Ar spec3 .Xc Set the BIOS geometry used in partition calculations. There must be three values specified, with a letter preceding each number: .Bl -tag -width Ds .Sm off .It Cm c Ar num .Sm on Set the number of cylinders to .Ar num . .Sm off .It Cm h Ar num .Sm on Set the number of heads to .Ar num . .Sm off .It Cm s Ar num .Sm on Set the number of sectors/track to .Ar num . .El .Pp These specs can occur in any order, as the leading letter determines which value is which; however, all three must be specified. .Pp This line must occur before any lines that specify partition information. .Pp It is an error if the following is not true: .Bd -literal -offset indent 1 <= number of cylinders 1 <= number of heads <= 256 1 <= number of sectors/track < 64 .Ed .Pp The number of cylinders should be less than or equal to 1024, but this is not enforced, although a warning will be output. Note that bootable .Fx partitions (the "/" file system) must lie completely within the first 1024 cylinders; if this is not true, booting may fail. Non-bootable partitions do not have this restriction. .Pp Example (all of these are equivalent), for a disk with 1019 cylinders, 39 heads, and 63 sectors: .Bd -literal -offset indent g c1019 h39 s63 g h39 c1019 s63 g s63 h39 c1019 .Ed .It Xo .Ic p .Ar partition .Ar type .Ar start .Ar length .Xc Set the partition given by .Ar partition (1-4) to type .Ar type , starting at sector .Ar start for .Ar length sectors. .Pp Only those partitions explicitly mentioned by these lines are modified; any partition not referenced by a "p" line will not be modified. However, if an invalid partition table is present, or the .Fl i option is specified, all existing partition entries will be cleared (marked as unused), and these "p" lines will have to be used to explicitly set partition information. If multiple partitions need to be set, multiple "p" lines must be specified; one for each partition. .Pp These partition lines must occur after any geometry specification lines, if one is present. .Pp The .Ar type is 165 for .Fx partitions. Specifying a partition type of zero is the same as clearing the partition and marking it as unused; however, dummy values (such as "0") must still be specified for .Ar start and .Ar length . .Pp Note: the start offset will be rounded upwards to a head boundary if necessary, and the end offset will be rounded downwards to a cylinder boundary if necessary. .Pp Example: to clear partition 4 and mark it as unused: .Bd -literal -offset indent p 4 0 0 0 .Ed .Pp Example: to set partition 1 to a .Fx partition, starting at sector 1 for 2503871 sectors (note: these numbers will be rounded upwards and downwards to correspond to head and cylinder boundaries): .Bd -literal -offset indent p 1 165 1 2503871 .Ed .It Xo .Ic a .Ar partition .Xc Make .Ar partition the active partition. Can occur anywhere in the config file, but only one must be present. .Pp Example: to make partition 1 the active partition: .Bd -literal -offset indent a 1 .Ed .El .Sh FILES .Bl -tag -width /boot/mbr -compact .It Pa /boot/mbr The default boot code .El .Sh SEE ALSO .Xr disklabel 8 .Sh BUGS The default boot code will not necessarily handle all partition types correctly, in particular those introduced since MS-DOS 6.x. .Pp The entire program should be made more user-friendly. .Pp Throughout this man page, the term .Sq partition is used where it should actually be .Sq slice , in order to conform with the terms used elsewhere. .Pp You cannot use this command to completely dedicate a disk to .Fx . The .Xr disklabel 8 command must be used for this.