1.\" $FreeBSD$ 2.\" 3.Dd April 30, 2007 4.Dt FDISK 8 5.Os 6.Sh NAME 7.Nm fdisk 8.Nd PC slice table maintenance utility 9.Sh SYNOPSIS 10.Nm 11.Op Fl BIaipqstu 12.Op Fl b Ar bootcode 13.Op Fl 1234 14.Op Ar disk 15.Nm 16.Fl f Ar configfile 17.Op Fl itv 18.Op Ar disk 19.Sh PROLOGUE 20In order for the BIOS to boot the kernel, 21certain conventions must be adhered to. 22Sector 0 of the disk must contain boot code, 23a slice table, 24and a magic number. 25BIOS slices can be used to break the disk up into several pieces. 26The BIOS brings in sector 0 and verifies the magic number. 27The sector 280 boot code then searches the slice table to determine which 29slice is marked 30.Dq active . 31This boot code then brings in the bootstrap from the 32active slice and, if marked bootable, runs it. 33Under 34.Tn DOS , 35you can have one or more slices with one active. 36The 37.Tn DOS 38.Nm 39utility can be used to divide space on the disk into slices and set one 40active. 41.Sh DESCRIPTION 42The 43.Fx 44utility, 45.Nm , 46serves a similar purpose to the 47.Tn DOS 48utility. 49The first form is used to 50display slice information or to interactively edit the slice 51table. 52The second is used to write a slice table using a 53.Ar configfile , 54and is designed to be used by other scripts/programs. 55.Pp 56Options are: 57.Bl -tag -width indent 58.It Fl a 59Change the active slice only. 60Ignored if 61.Fl f 62is given. 63.It Fl b Ar bootcode 64Get the boot code from the file 65.Ar bootcode . 66Default is 67.Pa /boot/mbr . 68.It Fl B 69Reinitialize the boot code contained in sector 0 of the disk. 70Ignored if 71.Fl f 72is given. 73.It Fl f Ar configfile 74Set slice values using the file 75.Ar configfile . 76The 77.Ar configfile 78only modifies explicitly specified slices, unless 79.Fl i 80is also given, in which case all existing slices are deleted (marked 81as 82.Dq unused ) 83before the 84.Ar configfile 85is read. 86The 87.Ar configfile 88can be 89.Sq Fl , 90in which case standard input is read. 91See 92.Sx CONFIGURATION FILE , 93below, for file syntax. 94.Pp 95.Em WARNING : 96when 97.Fl f 98is used, you are not asked if you really want to write the slices 99table (as you are in the interactive mode). 100Use with caution! 101.It Fl i 102Initialize sector 0 of the disk. 103Existing slice entries will be cleared 104(marked as unused) before editing. 105(Compare with 106.Fl u . ) 107.It Fl I 108Initialize sector 0 slice table 109for one 110.Fx 111slice covering the entire disk. 112.It Fl p 113Print a slice table in 114.Nm 115configuration file format and exit; see 116.Sx CONFIGURATION FILE , 117below. 118.It Fl q 119Be quiet. 120Benign warnings (such as "GEOM not found") are suppressed. 121.It Fl s 122Print summary information and exit. 123.It Fl t 124Test mode; do not write slice values. 125Generally used with the 126.Fl f 127option to see what would be written to the slice table. 128Implies 129.Fl v . 130.It Fl u 131Update (edit) the disk's sector 0 slice table. 132Ignored if 133.Fl f 134is given. 135.It Fl v 136Be verbose. 137When 138.Fl f 139is used, 140.Nm 141prints out the slice table that is written to the disk. 142.It Fl 1234 143Operate on a single slice table entry only. 144Ignored if 145.Fl f 146is given. 147.El 148.Pp 149The final disk name can be provided as a 150.Dq bare 151disk name only, e.g.\& 152.Pa da0 , 153or as a full pathname. 154If omitted, 155.Nm 156tries to figure out the default disk device name from the 157mounted root device. 158.Pp 159When called with no arguments, it prints the sector 0 slice table. 160An example follows: 161.Bd -literal 162 ******* Working on device /dev/ad0 ******* 163 parameters extracted from in-core disklabel are: 164 cylinders=769 heads=15 sectors/track=33 (495 blks/cyl) 165 166 parameters to be used for BIOS calculations are: 167 cylinders=769 heads=15 sectors/track=33 (495 blks/cyl) 168 169 Warning: BIOS sector numbering starts with sector 1 170 Information from DOS bootblock is: 171 The data for partition 1 is: 172 sysid 165,(FreeBSD/NetBSD/386BSD) 173 start 495, size 380160 (185 Meg), flag 0 174 beg: cyl 1/ sector 1/ head 0; 175 end: cyl 768/ sector 33/ head 14 176 The data for partition 2 is: 177 sysid 164,(unknown) 178 start 378180, size 2475 (1 Meg), flag 0 179 beg: cyl 764/ sector 1/ head 0; 180 end: cyl 768/ sector 33/ head 14 181 The data for partition 3 is: 182 <UNUSED> 183 The data for partition 4 is: 184 sysid 99,(ISC UNIX, other System V/386, GNU HURD or Mach) 185 start 380656, size 224234 (109 Meg), flag 80 186 beg: cyl 769/ sector 2/ head 0; 187 end: cyl 197/ sector 33/ head 14 188.Ed 189.Pp 190The disk is divided into three slices that happen to fill the disk. 191The second slice overlaps the end of the first. 192(Used for debugging purposes.) 193.Bl -tag -width ".Em cyl , sector No and Em head" 194.It Em sysid 195is used to label the slice. 196.Fx 197reserves the 198magic number 165 decimal (A5 in hex). 199.It Xo 200.Em start 201and 202.Em size 203.Xc 204fields provide the start address 205and size of a slice in sectors. 206.It Em "flag 80" 207specifies that this is the active slice. 208.It Xo 209.Em cyl , sector 210and 211.Em head 212.Xc 213fields are used to specify the beginning and end addresses of the slice. 214.El 215.Pp 216.Em Note : 217these numbers are calculated using BIOS's understanding of the disk geometry 218and saved in the bootblock. 219.Pp 220The 221.Fl i 222and 223.Fl u 224flags are used to indicate that the slice data is to be updated. 225Unless the 226.Fl f 227option is also given, 228.Nm 229will enter a conversational mode. 230In this mode, no changes will be written to disk unless you explicitly tell 231.Nm 232to. 233.Pp 234The 235.Nm 236utility will display each slice and ask whether you want to edit it. 237If you say yes, 238.Nm 239will step through each field, show you the old value, 240and ask you for a new one. 241When you are done with the slice, 242.Nm 243will display it and ask you whether it is correct. 244It will then proceed to the next entry. 245.Pp 246Getting the 247.Em cyl , sector , 248and 249.Em head 250fields correct is tricky, so by default, 251they will be calculated for you; 252you can specify them if you choose to though. 253.Pp 254After all the slices are processed, 255you are given the option to change the 256.Dq active 257slice. 258Finally, when all the new data for sector 0 has been accumulated, 259you are asked to confirm whether you really want to rewrite it. 260.Pp 261The difference between the 262.Fl u 263and 264.Fl i 265flags is that 266the 267.Fl u 268flag edits (updates) the existing slice parameters 269while the 270.Fl i 271flag is used to 272.Dq initialize 273them (old values will be ignored); 274if you edit the first slice, 275.Fl i 276will also set it up to use the whole disk for 277.Fx 278and make it active. 279.Sh NOTES 280The automatic calculation of starting cylinder etc.\& uses 281a set of figures that represent what the BIOS thinks the 282geometry of the drive is. 283These figures are taken from the in-core disklabel by default, 284but 285.Nm 286initially gives you an opportunity to change them. 287This allows you to create a bootblock that can work with drives 288that use geometry translation under the BIOS. 289.Pp 290If you hand craft your disk layout, 291please make sure that the 292.Fx 293slice starts on a cylinder boundary. 294.Pp 295Editing an existing slice will most likely result in the loss of 296all data in that slice. 297.Pp 298You should run 299.Nm 300interactively once or twice to see how it works. 301This is completely safe as long as you answer the last question 302in the negative. 303There are subtleties that 304.Nm 305detects that are not fully explained in this manual page. 306.Sh CONFIGURATION FILE 307When the 308.Fl f 309option is given, a disk's slice table can be written using values 310from a 311.Ar configfile . 312The syntax of this file is very simple; 313each line is either a comment or a specification, as follows: 314.Bl -tag -width indent 315.It Ic # Ar comment ... 316Lines beginning with a 317.Ic # 318are comments and are ignored. 319.It Ic g Ar spec1 spec2 spec3 320Set the BIOS geometry used in slice calculations. 321There must be 322three values specified, with a letter preceding each number: 323.Bl -tag -width indent 324.It Cm c Ns Ar num 325Set the number of cylinders to 326.Ar num . 327.It Cm h Ns Ar num 328Set the number of heads to 329.Ar num . 330.It Cm s Ns Ar num 331Set the number of sectors/track to 332.Ar num . 333.El 334.Pp 335These specs can occur in any order, as the leading letter determines 336which value is which; however, all three must be specified. 337.Pp 338This line must occur before any lines that specify slice 339information. 340.Pp 341It is an error if the following is not true: 342.Bd -literal -offset indent 3431 <= number of cylinders 3441 <= number of heads <= 256 3451 <= number of sectors/track < 64 346.Ed 347.Pp 348The number of cylinders should be less than or equal to 1024, but this 349is not enforced, although a warning will be printed. 350Note that bootable 351.Fx 352slices (the 353.Dq Pa / 354file system) must lie completely within the 355first 1024 cylinders; if this is not true, booting may fail. 356Non-bootable slices do not have this restriction. 357.Pp 358Example (all of these are equivalent), for a disk with 1019 cylinders, 35939 heads, and 63 sectors: 360.Bd -literal -offset indent 361g c1019 h39 s63 362g h39 c1019 s63 363g s63 h39 c1019 364.Ed 365.It Ic p Ar slice type start length 366Set the slice given by 367.Ar slice 368(1-4) to type 369.Ar type , 370starting at sector 371.Ar start 372for 373.Ar length 374sectors. 375.Pp 376Only those slices explicitly mentioned by these lines are modified; 377any slice not referenced by a 378.Ic p 379line will not be modified. 380However, if an invalid slice table is present, or the 381.Fl i 382option is specified, all existing slice entries will be cleared 383(marked as unused), and these 384.Ic p 385lines will have to be used to 386explicitly set slice information. 387If multiple slices need to be 388set, multiple 389.Ic p 390lines must be specified; one for each slice. 391.Pp 392These slice lines must occur after any geometry specification lines, 393if one is present. 394.Pp 395The 396.Ar type 397is 165 for 398.Fx 399slices. 400Specifying a slice type of zero is 401the same as clearing the slice and marking it as unused; however, 402dummy values (such as 403.Dq 0 ) 404must still be specified for 405.Ar start 406and 407.Ar length . 408.Pp 409Note: the start offset will be rounded upwards to a head boundary if 410necessary, and the end offset will be rounded downwards to a cylinder 411boundary if necessary. 412.Pp 413Example: to clear slice 4 and mark it as unused: 414.Pp 415.Dl "p 4 0 0 0" 416.Pp 417Example: to set slice 1 to a 418.Fx 419slice, starting at sector 1 420for 2503871 sectors (note: these numbers will be rounded upwards and 421downwards to correspond to head and cylinder boundaries): 422.Pp 423.Dl "p 1 165 1 2503871" 424.It Ic a Ar slice 425Make 426.Ar slice 427the active slice. 428Can occur anywhere in the config file, but only 429one must be present. 430.Pp 431Example: to make slice 1 the active slice: 432.Pp 433.Dl "a 1" 434.El 435.Sh FILES 436.Bl -tag -width ".Pa /boot/mbr" -compact 437.It Pa /boot/mbr 438The default boot code. 439.El 440.Sh SEE ALSO 441.Xr boot0cfg 8 , 442.Xr bsdlabel 8 , 443.Xr newfs 8 444.Sh BUGS 445The default boot code will not necessarily handle all slice types 446correctly, in particular those introduced since 447.Tn MS-DOS 4486.x. 449.Pp 450The entire utility should be made more user-friendly. 451.Pp 452Most users new to 453.Fx 454do not understand the difference between 455.Dq slice 456and 457.Dq partition , 458causing difficulty to adjust. 459.Pp 460You cannot use this command to completely dedicate a disk to 461.Fx . 462The 463.Xr bsdlabel 8 464command must be used for this. 465