1.\" $NetBSD: installboot.8,v 1.54 2006/06/20 05:37:24 jdc Exp $ 2.\" 3.\" Copyright (c) 2002-2003 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Luke Mewburn of Wasabi Systems. 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 3. All advertising materials mentioning features or use of this software 18.\" must display the following acknowledgement: 19.\" This product includes software developed by the NetBSD 20.\" Foundation, Inc. and its contributors. 21.\" 4. Neither the name of The NetBSD Foundation nor the names of its 22.\" contributors may be used to endorse or promote products derived 23.\" from this software without specific prior written permission. 24.\" 25.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 26.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 27.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 28.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 29.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 30.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 31.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 32.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 33.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 34.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 35.\" POSSIBILITY OF SUCH DAMAGE. 36.\" 37.Dd May 19, 2006 38.Dt INSTALLBOOT 8 39.Os 40.Sh NAME 41.Nm installboot 42.Nd install disk bootstrap software 43. 44.Sh SYNOPSIS 45.Nm 46.Op Fl nv 47.Op Fl B Ar s2bno 48.Op Fl b Ar s1bno 49.Op Fl m Ar machine 50.Op Fl o Ar options 51.Op Fl t Ar fstype 52.Ar filesystem 53.Ar primary 54.Op Ar secondary 55.Nm 56.Fl c 57.Op Fl nv 58.Op Fl m Ar machine 59.Op Fl o Ar options 60.Op Fl t Ar fstype 61.Ar filesystem 62.Nm 63.Fl e 64.Op Fl nv 65.Op Fl m Ar machine 66.Op Fl o Ar options 67.Ar bootstrap 68. 69.Sh DESCRIPTION 70The 71.Nm 72utility installs and removes 73.Nx 74disk bootstrap software into a file system. 75.Nm 76can install 77.Ar primary 78into 79.Ar filesystem , 80or disable an existing bootstrap in 81.Ar filesystem . 82.Pp 83Generally, 84.Nx 85disk bootstrap software consists of two parts: a 86.Dq primary 87bootstrap program usually written into the disklabel area of the 88file system by 89.Nm , 90and a 91.Dq secondary 92bootstrap program that usually resides as an ordinary file in the file system. 93.Pp 94When booting, the primary bootstrap program is loaded and invoked by 95the machine's PROM or BIOS. 96After receiving control of the system it loads and runs the secondary 97bootstrap program, which in turn loads and runs the kernel. 98The secondary bootstrap may allow control over various boot parameters 99passed to the kernel. 100.Pp 101Perform the following steps to make a file system bootable: 102.Bl -enum 103.It 104Copy the secondary bootstrap (usually 105.Pa /usr/mdec/boot. Ns Sy MACHINE 106or 107.Pa /usr/mdec/boot ) 108to the root directory of the target file system. 109.Pp 110. 111.It 112Use 113.Nm 114to install the primary bootstrap program 115(usually 116.Pa /usr/mdec/bootxx_ Ns Sy FSTYPE ) 117into 118.Ar filesystem . 119.Pp 120The following platforms do not require this step if the primary bootstrap 121already exists and the secondary bootstrap file is just being updated: 122.Sy alpha , 123.Sy amd64 , 124.Sy amiga , 125.Sy i386 , 126.Sy pmax , 127.Sy sparc64 , 128and 129.Sy vax . 130.Pp 131The following platform does not require the first step since a 132single bootstrap file is used. 133The single bootstrap is installed like the primary bootstrap on 134other platforms: 135.Sy next68k . 136.Pp 137.El 138.Pp 139The options and arguments recognized by 140.Nm 141are as follows: 142. 143.Bl -tag -width "optionsxxx" 144. 145.It Fl B Ar s2bno 146When hard-coding the blocks of 147.Ar secondary 148into 149.Ar primary , 150start from block 151.Ar s2bno 152instead of trying to determine the block numbers occupied by 153.Ar secondary 154by examining 155.Ar filesystem . 156If this option is supplied, 157.Ar secondary 158should refer to an actual secondary bootstrap (rather than the 159file name of the one present in 160.Ar filesystem ) 161so that its size can be determined. 162. 163.It Fl b Ar s1bno 164Install 165.Ar primary 166at block number 167.Ar s1bno 168instead of the default location for the machine and file system type. 169.Sy [ alpha , 170.Sy pmax , 171.Sy vax ] 172. 173.It Fl c 174Clear (remove) any existing bootstrap instead of installing one. 175. 176.It Fl e 177Edit the options of an existing bootstrap. 178.Sy [ amd64 , i386 ] 179. 180.It Fl m Ar machine 181Use 182.Ar machine 183as the target machine type. 184The default machine is determined from 185.Xr uname 3 186and then 187.Ev MACHINE . 188The following machines are currently supported by 189.Nm : 190.Bd -ragged -offset indent 191.Sy alpha , 192.Sy amd64 , 193.Sy amiga , 194.Sy ews4800mips , 195.Sy hp300 , 196.Sy hp700 , 197.Sy i386 , 198.Sy macppc , 199.Sy news68k , 200.Sy newsmips , 201.Sy next68k , 202.Sy pmax , 203.Sy sparc , 204.Sy sparc64 , 205.Sy sun2 , 206.Sy sun3 , 207.Sy vax , 208.Sy x68k 209.Ed 210. 211. 212.It Fl n 213Do not write to 214.Ar filesystem . 215. 216.It Fl o Ar options 217Machine specific 218.Nm 219options, comma separated. 220.Pp 221Supported options are (with the machines for they are valid in brackets): 222. 223.Bl -tag -offset indent -width alphasum 224. 225.It Sy alphasum 226.Sy [ alpha ] 227Recalculate and restore the Alpha checksum. 228This is the default for 229.Nx Ns Tn /alpha . 230. 231.It Sy append 232.Sy [ alpha , 233.Sy pmax , 234.Sy vax ] 235Append 236.Ar primary 237to the end of 238.Ar filesystem , 239which must be a regular file in this case. 240. 241.It Sy command=\*[Lt]boot command\*[Gt] 242.Sy [ amiga ] 243Modify the default boot command line. 244. 245.It Sy console=\*[Lt]console name\*[Gt] 246.Sy [ amd64 , 247.Sy i386 ] 248Set the console device, \*[Lt]console name\*[Gt] must be one of: 249pc, com0, com1, com2, com3, com0kbd, com1kbd, com2kbd or com3kbd. 250. 251.It Sy ioaddr=\*[Lt]ioaddr\*[Gt] 252.Sy [ amd64 , 253.Sy i386 ] 254Set the IO address to be used for the console serial port. 255Defaults to the IO address used by the system BIOS for the specified port. 256. 257.It Sy keymap=\*[Lt]keymap\*[Gt] 258.Sy [ amd64 , 259.Sy i386 ] 260Set a boot time keyboard translation map. 261Each character in \*[Lt]keymap\*[Gt] will be replaced by the one following it. 262For example, an argument of 263.Dq zyz 264would swap the lowercase letters 265.Sq y 266and 267.Sq z . 268. 269.It Sy password=\*[Lt]password\*[Gt] 270.Sy [ amd64 , 271.Sy i386 ] 272Set the password which must be entered before the boot menu can be accessed. 273. 274.It Sy resetvideo 275.Sy [ amd64 , 276.Sy i386 ] 277Reset the video before booting. 278. 279.It Sy speed=\*[Lt]baud rate\*[Gt] 280.Sy [ amd64 , 281.Sy i386 ] 282Set the baud rate for the serial console. 283If a value of zero is specified, then the current baud rate (set by the 284BIOS) will be used. 285. 286.It Sy sunsum 287.Sy [ alpha , 288.Sy pmax , 289.Sy vax ] 290Recalculate and restore the Sun and 291.Nx Ns Tn /sparc 292compatible checksum. 293.Em Note : 294The existing 295.Nx Ns Tn /sparc 296disklabel should use no more than 4 partitions. 297. 298.It Sy timeout=\*[Lt]seconds\*[Gt] 299.Sy [ amd64 , 300.Sy i386 ] 301Set the timeout before the automatic boot begins to the given number of seconds. 302.El 303. 304.It Fl t Ar fstype 305Use 306.Ar fstype 307as the type of 308.Ar filesystem . 309The default operation is to attempt to auto-detect this setting. 310The following file system types are currently supported by 311.Nm : 312. 313.Bl -tag -offset indent -width raid 314. 315.It Sy ffs 316.Bx 317Fast File System. 318. 319.It Sy raid 320Mirrored RAIDframe File System. 321. 322.It Sy raw 323.Sq Raw 324image. 325Note: if a platform needs to hard-code the block offset of the secondary 326bootstrap, it cannot be searched for on this file system type, and must 327be provided with 328.Fl B Ar s2bno . 329.El 330. 331.It Fl v 332Verbose operation. 333. 334.It Ar filesystem 335The path name of the device or file system image that 336.Nm 337is to operate on. 338It is not necessary for 339.Ar filesystem 340to be a currently mounted file system. 341. 342.It Ar primary 343The path name of the 344.Dq primary 345boot block to install. 346. 347.It Ar secondary 348The path name of the 349.Dq secondary 350boot block, 351relative to the top of 352.Ar filesystem . 353Most systems require 354.Ar secondary 355to be in the 356.Dq root 357directory of the file system, so the leading 358.Dq Pa / 359is not necessary on 360.Ar secondary . 361.Pp 362Only certain combinations of 363platform 364.Pq Fl m Ar machine 365and file system type 366.Pq Fl t Ar fstype 367require that the name of the secondary bootstrap is 368supplied as 369.Ar secondary , 370so that information such as the disk block numbers occupied 371by the secondary bootstrap can be stored in the primary bootstrap. 372These are: 373.Bl -column "Platform" "File systems" -offset indent 374.It Sy "Platform" Ta Sy "File systems" 375.It macppc Ta ffs, raw 376.It news68k Ta ffs, raw 377.It newsmips Ta ffs, raw 378.It sparc Ta ffs, raid, raw 379.It sun2 Ta ffs, raw 380.It sun3 Ta ffs, raw 381.El 382.El 383.Pp 384.Nm 385exits 0 on success, and \*[Gt]0 if an error occurs. 386. 387.Sh ENVIRONMENT 388.Nm 389uses the following environment variables: 390. 391.Bl -tag -width "MACHINE" 392. 393.It Ev MACHINE 394Default value for 395.Ar machine , 396overriding the result from 397.Xr uname 3 . 398. 399.El 400. 401.Sh FILES 402Most 403.Nx 404ports will contain variations of the following files: 405.Pp 406.Bl -tag -width /usr/mdec/bootxx_ustarfs 407. 408.It Pa /usr/mdec/bootxx_ Ns Sy FSTYPE 409Primary bootstrap for file system type 410.Sy FSTYPE . 411Installed into the bootstrap area of the file system by 412.Nm . 413. 414.It Pa /usr/mdec/bootxx_ffsv1 415Primary bootstrap for 416.Sy FFSv1 417file systems 418(the "traditional" 419.Nx 420file system). 421. 422.It Pa /usr/mdec/bootxx_ffsv2 423Primary bootstrap for 424.Sy FFSv2 425file systems. 426. 427.It Pa /usr/mdec/bootxx_lfsv1 428Primary bootstrap for 429.Sy LFSv1 430file systems. 431. 432.It Pa /usr/mdec/bootxx_lfsv2 433Primary bootstrap for 434.Sy LFSv2 435file systems 436(the default LFS version). 437. 438.It Pa /usr/mdec/bootxx_msdos 439Primary bootstrap for 440.Tn MS-DOS 441.Sy FAT 442file systems. 443. 444.It Pa /usr/mdec/bootxx_ustarfs 445Primary bootstrap for 446.Sy TARFS 447boot images. 448This is used by various install media. 449. 450.It Pa /usr/mdec/boot. Ns Sy MACHINE 451Secondary bootstrap for machine type 452.Sy MACHINE . 453This should be installed into the file system before 454.Nm 455is run. 456. 457.It Pa /usr/mdec/boot 458Synonym for 459.Pa /usr/mdec/boot. Ns Sy MACHINE 460. 461.It Pa /boot. Ns Sy MACHINE 462Installed copy of secondary bootstrap for machine type 463.Sy MACHINE . 464. 465.It Pa /boot 466Installed copy of secondary bootstrap. 467Searched for by the primary bootstrap if 468.Pa /boot. Ns Sy MACHINE 469is not found. 470. 471.El 472. 473.Ss Nx Ns Tn /next68k files 474. 475.Bl -tag -width /usr/mdec/bootxx_ustarfs 476. 477.It Pa /usr/mdec/boot 478.Nx Ns Tn /next68k 479bootstrap. 480. 481.El 482. 483.Ss Nx Ns Tn /sparc64 files 484. 485.Bl -tag -width /usr/mdec/bootxx_ustarfs 486. 487.It Pa /usr/mdec/bootblk 488.Nx Ns Tn /sparc64 489primary bootstrap. 490. 491.It Pa /usr/mdec/ofwboot 492.Nx Ns Tn /sparc64 493secondary bootstrap. 494. 495.It Pa /ofwboot 496Installed copy of 497.Nx Ns Tn /sparc64 498secondary bootstrap. 499. 500.El 501. 502.Sh EXAMPLES 503. 504.Ss common 505Verbosely install the Berkeley Fast File System primary bootstrap on to disk 506.Sq sd0 : 507.Dl Ic installboot -v /dev/rsd0c /usr/mdec/bootxx_ffs 508.Pp 509Remove the primary bootstrap from disk 510.Sq sd1 : 511.Dl Ic installboot -c /dev/rsd1c 512. 513.Ss Nx Ns Tn /amiga 514Modify the command line to change the default from "netbsd -ASn2" to 515"netbsd -S": 516.Dl Ic installboot -m amiga -o command="netbsd -S" /dev/rsd0a /usr/mdec/bootxx_ffs 517. 518.Ss Nx Ns Tn /ews4800mips 519Install the System V Boot File System primary bootstrap on to disk 520.Sq sd0 , 521with the secondary bootstrap 522.Sq Pa /boot 523already present in the SysVBFS partition on the disk: 524.Dl Ic installboot /dev/rsd0c /usr/mdec/bootxx_bfs 525. 526.Ss Nx Ns Tn /i386 and Nx Ns Tn /amd64 527Install new boot blocks on an existing mounted root file system on 528.Sq wd0 , 529setting the timeout to five seconds, after copying a new secondary 530bootstrap: 531.Dl Ic cp /usr/mdec/boot /boot 532.Dl Ic installboot -v -o timeout=5 /dev/rwd0a /usr/mdec/bootxx_ffsv1 533. 534.Pp 535Create a bootable CD-ROM with an ISO9660 536file system for a system with a serial console: 537.Dl Ic mkdir cdrom 538.Dl Ic cp sys/arch/i386/compile/mykernel/netbsd cdrom/netbsd 539.Dl Ic cp /usr/mdec/boot cdrom/boot 540.Dl Ic cp /usr/mdec/bootxx_cd9660 bootxx 541.Dl Ic installboot -t raw -o console=com0,speed=19200 bootxx \ 542 /usr/mdec/bootxx_cd9660 543.Dl Ic makefs -t cd9660 -o 'bootimage=i386;bootxx,no-emul-boot' boot.iso \ 544 cdrom 545. 546.Pp 547Create a bootable floppy disk with an FFSv1 548file system for a small custom kernel (note: bigger kernels needing 549multiple disks are handled with the ustarfs file system): 550.Dl Ic newfs -s 1440k /dev/rfd0a 551.Bd -ragged -offset indent-two -compact 552.Em Note : 553Ignore the warnings that 554.Xr newfs 8 555displays; it can not write a disklabel, 556which is not a problem for a floppy disk. 557.Ed 558.Dl Ic mount /dev/fd0a /mnt 559.Dl Ic cp /usr/mdec/boot /mnt/boot 560.Dl Ic gzip -9 \*[Lt] sys/arch/i386/compile/mykernel/netbsd \*[Gt] /mnt/netbsd.gz 561.Dl Ic umount /mnt 562.Dl Ic installboot -v /dev/rfd0a /usr/mdec/bootxx_ffsv1 563. 564.Pp 565Create a bootable FAT file system on 566.Sq wd1a , 567which should have the same offset and size as a FAT primary partition 568in the Master Boot Record (MBR): 569.Dl Ic newfs_msdos -r 16 /dev/rwd1a 570.Bd -ragged -offset indent-two -compact 571.Em Notes : 572The 573.Fl r Ar 16 574is to reserve space for the primary bootstrap. 575.Xr newfs_msdos 8 576will display an 577.Dq MBR type 578such as 579.Ql 1 , 580.Ql 4 , 581or 582.Ql 6 ; 583the MBR partition type of the appropriate primary partition should be 584changed to this value. 585.Ed 586.Dl Ic mount -t msdos /dev/wd1a /mnt 587.Dl Ic cp /usr/mdec/boot /mnt/boot 588.Dl Ic cp path/to/kernel /mnt/netbsd 589.Dl Ic umount /mnt 590.Dl Ic installboot -t raw /dev/rwd1a /usr/mdec/bootxx_msdos 591.Bd -ragged -offset indent-two -compact 592.Em Note : 593It may be necessary to ensure that there is a valid 594.Nx 595disklabel on 596.Sq wd1 597for the primary bootstrap to function correctly. 598.Ed 599. 600.Ss Nx Ns Tn /next68k 601Install the bootstrap on to disk 602.Sq sd0 : 603.Dl Ic installboot /dev/rsd0c /usr/mdec/boot 604.Pp 605. 606.Ss Nx Ns Tn /pmax 607Install the Berkeley Fast File System primary bootstrap on to disk 608.Sq sd0 : 609.Dl Ic installboot /dev/rsd0c /usr/mdec/bootxx_ffs 610.Pp 611.Nx Ns Tn /pmax 612requires that this file system starts at block 0 of the disk. 613.Pp 614Install the ISO 9660 primary bootstrap in the file 615.Pa /tmp/cd-image : 616.Dl Ic installboot -m pmax /tmp/cd-image /usr/mdec/bootxx_cd9660 617.Pp 618Make an ISO 9660 filesystem in the file 619.Pa /tmp/cd-image 620and install the ISO 9660 primary bootstrap in the filesystem, where the 621source directory for the ISO 9660 filesystem contains a kernel, the 622primary bootstrap 623.Pa bootxx_cd9660 624and the secondary bootstrap 625.Pa boot.pmax : 626.Dl Ic mkisofs -o /tmp/cd-image -a -l -v iso-source-dir 627.Dl ... 628.Dl 48 51 iso-source-dir/bootxx_cd9660 629.Dl ... 630.Dl Ic installboot -b `expr 48 \e* 4` /tmp/cd-image /usr/mdec/bootxx_cd9660 631. 632.Ss Nx Ns Tn /sparc 633Install the Berkeley Fast File System primary bootstrap on to disk 634.Sq sd0 , 635with the secondary bootstrap 636.Sq Pa /boot 637already present: 638.Dl Ic installboot /dev/rsd0c /usr/mdec/bootxx /boot 639. 640.Ss Nx Ns Tn /sparc64 641Install the Berkeley Fast File System primary bootstrap on to disk 642.Sq wd0 : 643.Dl Ic installboot /dev/rwd0c /usr/mdec/bootblk 644.Pp 645The secondary 646.Nx Ns Tn /sparc64 647bootstrap is located in 648.Pa /usr/mdec/ofwboot . 649. 650.Ss Nx Ns Tn /sun2 and Nx Ns Tn /sun3 651Install the Berkeley Fast File System primary bootstrap on to disk 652.Sq sd0 , 653with the secondary bootstrap 654.Sq Pa /boot 655already present: 656.Dl Ic installboot /dev/rsd0c /usr/mdec/bootxx /boot 657. 658.Sh SEE ALSO 659.Xr uname 3 , 660.Xr boot 8 , 661.Xr disklabel 8 662. 663.Sh HISTORY 664This implementation of 665.Nm 666appeared in 667.Nx 1.6 . 668. 669.Sh AUTHORS 670The machine independent portion of this implementation of 671.Nm 672was written by Luke Mewburn. 673The following people contributed to the various machine dependent 674back-ends: 675Simon Burge (pmax), 676Chris Demetriou (alpha), 677Matthew Fredette (sun2, sun3), 678Matthew Green (sparc64), 679Ross Harvey (alpha), 680Michael Hitch (amiga), 681Paul Kranenburg (sparc), 682David Laight (i386), 683Christian Limpach (next68k), 684Luke Mewburn (macppc), 685Matt Thomas (vax), 686Izumi Tsutsui (news68k, newsmips), 687and 688UCHIYAMA Yasushi (ews4800mips). 689. 690.Sh BUGS 691There are not currently primary bootstraps to support all file systems 692types which are capable of being the root file system. 693.Pp 694If a disk has been converted from 695.Sy FFS 696to 697.Sy RAID 698without the contents of the disk erased, then the original 699.Sy FFS 700installation may be auto-detected instead of the 701.Sy RAID 702installation. In this case, the 703.Fl t Ar raid 704option must be provided. 705. 706.Ss Nx Ns Tn /alpha 707The 708.Nx Ns Tn /alpha 709primary bootstrap program can only load the secondary bootstrap program 710from file systems starting at the beginning (block 0) of disks. 711Similarly, the secondary bootstrap program can only load kernels from 712file systems starting at the beginning of disks. 713.Pp 714The size of primary bootstrap programs is restricted to 7.5KB, even 715though some file systems (e.g., ISO 9660) are able to accommodate larger 716ones. 717. 718.Ss Nx Ns Tn /hp300 719The disk must have a boot partition large enough to hold the bootstrap code. 720Currently the primary bootstrap must be a LIF format file. 721. 722.Ss Nx Ns Tn /i386 and Nx Ns Tn /amd64 723The bootstrap must be installed in the 724.Nx 725partition that starts at the beginning of the mbr partition. 726If that is a valid filesystem and contains the 727.Pa /boot 728program then it will be used as the root filesystem, otherwise the 729.Sq a 730partition will be booted. 731.Pp 732The size of primary bootstrap programs is restricted to 8KB, even 733though some file systems (e.g., ISO 9660) are able to accommodate larger 734ones. 735. 736.Ss Nx Ns Tn /next68k 737The size of bootstrap programs is restricted to the free space before 738the file system at the beginning of the disk minus 8KB. 739. 740.Ss Nx Ns Tn /pmax 741The 742.Nx Ns Tn /pmax 743secondary bootstrap program can only load kernels from file 744systems starting at the beginning of disks. 745.Pp 746The size of primary bootstrap programs is restricted to 7.5KB, even 747though some file systems (e.g., ISO 9660) are able to accommodate larger 748ones. 749. 750.Ss Nx Ns Tn /sun2 and Nx Ns Tn /sun3 751The 752.Nx Ns Tn /sun2 753and 754.Nx Ns Tn /sun3 755secondary bootstrap program can only load kernels from file 756systems starting at the beginning of disks. 757. 758.Ss Nx Ns Tn /vax 759The 760.Nx Ns Tn /vax 761secondary bootstrap program can only load kernels from file systems 762starting at the beginning of disks. 763.Pp 764The size of primary bootstrap programs is restricted to 7.5KB, even 765though some file systems (e.g., ISO 9660) are able to accommodate larger 766ones. 767