3 A bootloader for Linux using MS-DOS floppies
5 Copyright (C) 1994-2003 H. Peter Anvin
7 This program is provided under the terms of the GNU General Public
8 License, version 2 or, at your option, any later version. There is no
9 warranty, neither expressed nor implied, to the function of this
10 program. Please see the included file COPYING for details.
12 ----------------------------------------------------------------------
14 SYSLINUX now has a home page at http://syslinux.zytor.com/
16 ----------------------------------------------------------------------
18 SYSLINUX is a boot loader for the Linux operating system which
19 operates off an MS-DOS/Windows FAT filesystem. It is intended to
20 simplify first-time installation of Linux, and for creation of rescue-
21 and other special-purpose boot disks.
23 SYSLINUX can be used, when properly set up, completely eliminate the
24 need for distribution of raw diskette images for boot floppies. A
25 SYSLINUX floppy can be manipulated using standard MS-DOS (or any other
26 OS that can access an MS-DOS filesystem) tools once it has been
30 ++++ WHAT SYSLINUX IS NOT ++++
32 SYSLINUX is probably not suitable as a general purpose boot loader.
33 It can only boot Linux from a FAT filesystem, and not, for example,
34 ext2. Since a native Linux implementation will typically use ext2,
35 another boot loader (e.g. LILO) is probably more suitable. In a
36 system which actually contains DOS or Windows, LOADLIN may be simpler
39 However, SYSLINUX has shown itself to be quite useful in a number of
40 special-purpose applications.
43 ++++ CREATING A BOOTABLE LINUX FLOPPY +++
45 In order to create a bootable Linux floppy using SYSLINUX, prepare a
46 normal MS-DOS formatted floppy. Copy one or more Linux kernel files to
47 it, then execute the DOS command:
51 (or whichever drive letter is appropriate; the [] meaning -s is optional)
53 If you're running in a Win95/98/ME DOS box, you should execute the
54 command "lock a:" first. If you're running in a WinNT/2K DOS box, you
55 will probably get a dialog box about not getting exclusive access and
56 with Abort/Retry/Ignore buttons; people have reported that selecting
57 "Ignore" makes the command complete correctly.
59 Under Linux, execute the command:
61 syslinux [-s] [-o offset] /dev/fd0
63 (or, again, whichever device is the correct one.)
65 This will alter the boot sector on the disk and copy a file named
66 LDLINUX.SYS into its root directory.
68 The -s option, if given, will install a "safe, slow and stupid"
69 version of SYSLINUX. This version may work on some very buggy BIOSes
70 on which SYSLINUX would otherwise fail. If you find a machine on
71 which the -s option is required to make it boot reliably, please send
72 as much info about your machine as you can, and include the failure
75 The -o option is used with a disk image file and specifies the byte
76 offset of the filesystem image in the file.
78 On boot time, by default, the kernel will be loaded from the image named
79 LINUX on the boot floppy. This default can be changed, see the section
80 on the SYSLINUX config file.
82 If the Shift or Alt keys are held down during boot, or the Caps or Scroll
83 locks are set, SYSLINUX will display a LILO-style "boot:" prompt. The
84 user can then type a kernel file name followed by any kernel parameters.
85 The SYSLINUX loader does not need to know about the kernel file in
86 advance; all that is required is that it is a file located in the root
87 directory on the disk.
90 ++++ CONFIGURATION FILE ++++
92 All the configurable defaults in SYSLINUX can be changed by putting a
93 file called SYSLINUX.CFG in the root directory of the boot floppy. This
94 is a text file in either UNIX or DOS format, containing one or more of
95 the following items (case is insensitive for keywords; upper case is used
96 here to indicate that a word should be typed verbatim):
98 All options here applies to PXELINUX as well as SYSLINUX unless
99 otherwise noted. See pxelinux.doc for additional information on
103 A comment line. The whitespace after the hash mark is mandatory.
105 DEFAULT kernel options...
106 Sets the default command line. If SYSLINUX boots automatically,
107 it will act just as if the entries after DEFAULT had been typed
108 in at the "boot:" prompt.
110 If no configuration file is present, or no DEFAULT entry is
111 present in the config file, the default is "linux auto".
113 NOTE: Earlier versions of SYSLINUX used to automatically
114 append the string "auto" to whatever the user specified using
115 the DEFAULT command. As of version 1.54, this is no longer
116 true, as it caused problems when using a shell as a substitute
117 for "init." You may want to include this option manually.
120 Add one or more options to the kernel command line. These are
121 added both for automatic and manual boots. The options are
122 added at the very beginning of the kernel command line,
123 usually permitting explicitly entered kernel options to override
124 them. This is the equivalent of the LILO "append" option.
126 IPAPPEND flag_val [PXELINUX only]
127 The IPAPPEND option is available only on PXELINUX. The
128 flag_val is an OR of the following options:
130 1: indicates that an option of the following format
131 should be generated and added to the kernel command line:
133 ip=<client-ip>:<boot-server-ip>:<gw-ip>:<netmask>
135 ... based on the input from the DHCP/BOOTP or PXE boot server.
137 THE USE OF THIS OPTION IS NOT RECOMMENDED. If you have to use
138 it, it is probably an indication that your network configuration
139 is broken. Using just "ip=dhcp" on the kernel command line
140 is a preferrable option, or, better yet, run dhcpcd/dhclient,
141 from an initrd if necessary.
143 2: indicates that an option of the following format
144 should be generated and added to the kernel command line:
146 BOOTIF=<hardware-address-of-boot-interface>
148 ... in dash-separated hexadecimal with leading hardware type
149 (same as for the configuration file; see pxelinux.doc.)
151 This allows an initrd program to determine from which
152 interface the system booted.
157 IPAPPEND flag_val [PXELINUX only]
158 Indicates that if "label" is entered as the kernel to boot,
159 SYSLINUX should instead boot "image", and the specified APPEND
160 and IPAPPEND options should be used instead of the ones
161 specified in the global section of the file (before the first
162 LABEL command.) The default for "image" is the same as
163 "label", and if no APPEND is given the default is to use the
164 global entry (if any). Up to 64 LABEL entries are permitted
165 (for SYSLINUX, 128 LABEL entries.)
167 Note that LILO uses the syntax:
172 ... whereas SYSLINUX uses the syntax:
177 Notes: Labels are mangled as if they were filenames, and must be
178 unique after mangling. For example, two labels
179 "v2.1.30" and "v2.1.31" will not be distinguishable
180 under SYSLINUX, since both mangle to the same DOS filename.
182 The "kernel" doesn't have to be a Linux kernel; it can
183 be a boot sector or a COMBOOT file (see below.)
186 Append nothing. APPEND with a single hyphen as argument in a
187 LABEL section can be used to override a global APPEND.
189 LOCALBOOT type [ISOLINUX, PXELINUX]
190 On PXELINUX, specifying "LOCALBOOT 0" instead of a "KERNEL"
191 option means invoking this particular label will cause a local
192 disk boot instead of booting a kernel.
194 The argument 0 means perform a normal boot. The argument 4
195 will perform a local boot with the Universal Network Driver
196 Interface (UNDI) driver still resident in memory. Finally,
197 the argument 5 will perform a local boot with the entire PXE
198 stack, including the UNDI driver, still resident in memory.
199 All other values are undefined. If you don't know what the
200 UNDI or PXE stacks are, don't worry -- you don't want them,
203 On ISOLINUX, the "type" specifies the local drive number to
204 boot from; 0x00 is the primary floppy drive and 0x80 is the
205 primary hard drive. The special value -1 causes ISOLINUX to
206 report failure to the BIOS, which, on recent BIOSes, should
207 mean that the next boot device in the boot sequence should be
211 If flag_val is 0, do not load a kernel image unless it has been
212 explicitly named in a LABEL statement. The default is 1.
214 ALLOWOPTIONS flag_val
215 If flag_val is 0, the user is not allowed to specify any
216 arguments on the kernel command line. The only options
217 recognized are those specified in an APPEND statement. The
221 Indicates how long to wait at the boot: prompt until booting
222 automatically, in units of 1/10 s. The timeout is cancelled as
223 soon as the user types anything on the keyboard, the assumption
224 being that the user will complete the command line already
225 begun. A timeout of zero will disable the timeout completely,
226 this is also the default.
228 NOTE: The maximum possible timeout value is 35996; corresponding to
231 ONTIMEOUT kernel options...
232 Sets the command line invoked on a timeout. Normally this is
233 the same thing as invoked by "DEFAULT". If this is specified,
234 then "DEFAULT" is used only if the user presses <Enter> to
237 ONERROR kernel options...
238 If a kernel image is not found (either due to it not existing,
239 or because IMPLICIT is set), run the specified command. The
240 faulty command line is appended to the specified options, so
241 if the ONERROR directive reads as:
245 ... and the command line as entered by the user is:
249 ... SYSLINUX will execute the following as if entered by the
252 xyzzy plugh foo bar baz
254 SERIAL port [[baudrate] flowcontrol]
255 Enables a serial port to act as the console. "port" is a
256 number (0 = /dev/ttyS0 = COM1, etc.) or an I/O port address
257 (e.g. 0x3F8); if "baudrate" is omitted, the baud rate defaults
258 to 9600 bps. The serial parameters are hardcoded to be 8
259 bits, no parity, 1 stop bit.
261 "flowcontrol" is a combination of the following bits:
264 0x010 - Wait for CTS assertion
265 0x020 - Wait for DSR assertion
266 0x040 - Wait for RI assertion
267 0x080 - Wait for DCD assertion
268 0x100 - Ignore input unless CTS asserted
269 0x200 - Ignore input unless DSR asserted
270 0x400 - Ignore input unless RI asserted
271 0x800 - Ignore input unless DCD asserted
273 All other bits are reserved.
277 0 - No flow control (default)
278 0x303 - Null modem cable detect
279 0x013 - RTS/CTS flow control
280 0x813 - RTS/CTS flow control, modem input
281 0x023 - DTR/DSR flow control
282 0x083 - DTR/DCD flow control
284 For the SERIAL directive to be guaranteed to work properly, it
285 should be the first directive in the configuration file.
287 NOTE: "port" values from 0 to 3 means the first four serial
288 ports detected by the BIOS. They may or may not correspond to
289 the legacy port values 0x3F8, 0x2F8, 0x3E8, 0x2E8.
292 Load a font in .psf format before displaying any output
293 (except the copyright line, which is output as ldlinux.sys
294 itself is loaded.) SYSLINUX only loads the font onto the
295 video card; if the .psf file contains a Unicode table it is
296 ignored. This only works on EGA and VGA cards; hopefully it
297 should do nothing on others.
300 Install a simple keyboard map. The keyboard remapper used is
301 *very* simplistic (it simply remaps the keycodes received from
302 the BIOS, which means that only the key combinations relevant
303 in the default layout -- usually U.S. English -- can be
304 mapped) but should at least help people with AZERTY keyboard
305 layout and the locations of = and , (two special characters
306 used heavily on the Linux kernel command line.)
308 The included program keytab-lilo.pl from the LILO distribution
309 can be used to create such keymaps. The file keytab-lilo.doc
310 contains the documentation for this program.
313 Displays the indicated file on the screen at boot time (before
314 the boot: prompt, if displayed). Please see the section below
317 NOTE: If the file is missing, this option is simply ignored.
320 Prints the message on the screen.
323 If flag_val is 0, display the boot: prompt only if the Shift or Alt
324 key is pressed, or Caps Lock or Scroll lock is set (this is the
325 default). If flag_val is 1, always display the boot: prompt.
332 Displays the indicated file on the screen when a function key is
333 pressed at the boot: prompt. This can be used to implement
334 pre-boot online help (presumably for the kernel command line
335 options.) Note that F10 MUST be entered in the config file as
336 "F0", not "F10", and that there is currently no way to bind
337 file names to F11 and F12. Please see the section below on
340 When using the serial console, press <Ctrl-F><digit> to get to
341 the help screens, e.g. <Ctrl-F><2> to get to the F2 screen,
342 and <Ctrl-F><0> for the F10 one.
344 Blank lines are ignored.
346 Note that the configuration file is not completely decoded. Syntax
347 different from the one described above may still work correctly in this
348 version of SYSLINUX, but may break in a future one.
351 ++++ LARGE KERNELS AND INITIAL RAMDISK SUPPORT ++++
353 This version of SYSLINUX supports large kernels (bzImage format),
354 eliminating the 500K size limit of the zImage kernel format. bzImage
355 format kernels are detected automatically and handled transparently to
358 This version of SYSLINUX also supports a boot-time-loaded ramdisk
359 (initrd). An initrd is loaded from a DOS file if the option
360 "initrd=filename" (where filename is the filename of the initrd image;
361 the file must be located in the root directory on the boot floppy) is
362 present on the processed command line (after APPEND's have been added,
363 etc.). If several initrd options are present, the last one has
364 precedence; this permits user-entered options to override a config
365 file APPEND. Specifying "initrd=" without a filename inhibits initrd
366 loading. The file specified by the initrd= option will typically be a
367 gzipped filesystem image.
369 NOTE: One of the main advantages with SYSLINUX is that it makes it
370 very easy to support users with new or unexpected configurations,
371 especially in a distribution setting. If initrd is used to
372 extensively modularize the distribution kernel, it is strongly
373 recommended that a simple way of adding drivers to the boot floppy be
374 provided. The suggested manner is to let the initrd system mount the
375 boot floppy and look for additional drivers in a predetermined
378 To bzImage and recent zImage kernels, SYSLINUX 1.30 and higher will
379 identify using the ID byte 0x31. PXELINUX identifies using the ID
380 byte 0x32, and ISOLINUX 0x33. The ID range 0x34-0x3f is reserved for
381 future versions or derivatives of SYSLINUX.
384 ++++ DISPLAY FILE FORMAT ++++
386 DISPLAY and function-key help files are text files in either DOS or UNIX
387 format (with or without <CR>). In addition, the following special codes
390 <FF> <FF> = <Ctrl-L> = ASCII 12
391 Clear the screen, home the cursor. Note that the screen is
392 filled with the current display color.
394 <SI><bg><fg> <SI> = <Ctrl-O> = ASCII 15
395 Set the display colors to the specified background and
396 foreground colors, where <bg> and <fg> are hex digits,
397 corresponding to the standard PC display attributes:
399 0 = black 8 = dark grey
400 1 = dark blue 9 = bright blue
401 2 = dark green a = bright green
402 3 = dark cyan b = bright cyan
403 4 = dark red c = bright red
404 5 = dark purple d = bright purple
406 7 = light grey f = white
408 Picking a bright color (8-f) for the background results in the
409 corresponding dark color (0-7), with the foreground flashing.
411 Colors are not visible over the serial console.
413 <CAN>filename<newline> <CAN> = <Ctrl-X> = ASCII 24
414 If a VGA display is present, enter graphics mode and display
415 the graphic included in the specified file. The file format
416 is an ad hoc format called LSS16; the included Perl program
417 "ppmtolss16" can be used to produce these images. This Perl
418 program also includes the file format specification.
420 The image is displayed in 640x480 16-color mode. Once in
421 graphics mode, the display attributes (set by <SI> code
422 sequences) work slightly differently: the background color is
423 ignored, and the foreground colors are the 16 colors specified
424 in the image file. For that reason, ppmtolss16 allows you to
425 specify that certain colors should be assigned to specific
428 Color indicies 0 and 7, in particular, should be chosen with
429 care: 0 is the background color, and 7 is the color used for
430 the text printed by SYSLINUX itself.
432 <EM> <EM> = <Ctrl-Y> = ASCII 25
433 If we are currently in graphics mode, return to text mode.
435 <DLE>..<ETB> <Ctrl-P>..<Ctrl-W> = ASCII 16-23
436 These codes can be used to select which modes to print a
437 certain part of the message file in. Each of these control
438 characters select a specific set of modes (text screen,
439 graphics screen, serial port) for which the output is actually
442 Character Text Graph Serial
443 ------------------------------------------------------
444 <DLE> = <Ctrl-P> = ASCII 16 No No No
445 <DC1> = <Ctrl-Q> = ASCII 17 Yes No No
446 <DC2> = <Ctrl-R> = ASCII 18 No Yes No
447 <DC3> = <Ctrl-S> = ASCII 19 Yes Yes No
448 <DC4> = <Ctrl-T> = ASCII 20 No No Yes
449 <NAK> = <Ctrl-U> = ASCII 21 Yes No Yes
450 <SYN> = <Ctrl-V> = ASCII 22 No Yes Yes
451 <ETB> = <Ctrl-W> = ASCII 23 Yes Yes Yes
455 <DC1>Text mode<DC2>Graphics mode<DC4>Serial port<ETB>
457 ... will actually print out which mode the console is in!
459 <SUB> <SUB> = <Ctrl-Z> = ASCII 26
460 End of file (DOS convention).
463 ++++ COMBOOT IMAGES AND OTHER OPERATING SYSTEMS ++++
465 This version of SYSLINUX supports chain loading of other operating
466 systems (such as MS-DOS and its derivatives, including Windows 95/98),
467 as well as COMBOOT-style standalone executables (a subset of DOS .COM
468 files; see separate section below.)
470 Chain loading requires the boot sector of the foreign operating system
471 to be stored in a file in the root directory of the filesystem.
472 Because neither Linux kernels, boot sector images, nor COMBOOT files
473 have reliable magic numbers, SYSLINUX will look at the file extension.
474 The following extensions are recognized (case insensitive):
476 none or other Linux kernel image
477 .0 PXE bootstrap program (NBP) [PXELINUX only]
478 .bin "CD boot sector" [ISOLINUX only]
479 .bs Boot sector [SYSLINUX only]
480 .bss Boot sector, DOS superblock will be patched in [SYSLINUX only]
481 .c32 COM32 image (32-bit COMBOOT)
482 .cbt COMBOOT image (not runnable from DOS)
483 .com COMBOOT image (runnable from DOS)
484 .img Disk image [ISOLINUX only]
486 For filenames given on the command line, SYSLINUX will search for the
487 file by adding extensions in the order listed above if the plain
488 filename is not found. Filenames in KERNEL statements must be fully
492 ++++ BOOTING DOS (OR OTHER SIMILAR OPERATING SYSTEMS) ++++
494 This section applies to SYSLINUX only, not to PXELINUX or ISOLINUX.
495 See isolinux.doc for an equivalent procedure for ISOLINUX.
497 This is the recommended procedure for creating a SYSLINUX disk that
498 can boot either DOS or Linux. This example assumes the drive is A: in
499 DOS and /dev/fd0 in Linux; for other drives, substitute the
500 appropriate drive designator.
502 ---- Linux procedure ----
504 1. Make a DOS bootable disk. This can be done either by specifying
505 the /s option when formatting the disk in DOS, or by running the
506 DOS command SYS (this can be done under DOSEMU if DOSEMU has
507 direct device access to the relevant drive):
513 2. Boot Linux. Copy the DOS boot sector from the disk into a file:
515 dd if=/dev/fd0 of=dos.bss bs=512 count=1
517 3. Run SYSLINUX on the disk:
521 4. Mount the disk and copy the DOS boot sector file to it. The file
522 *must* have extension .bss:
524 mount -t msdos /dev/fd0 /mnt
527 5. Copy the Linux kernel image(s), initrd(s), etc to the disk, and
528 create/edit syslinux.cfg and help files if desired:
533 6. Unmount the disk (if applicable.)
537 ---- DOS/Windows procedure ----
539 To make this installation in DOS only, you need the utility copybs.com
540 (included with SYSLINUX) as well as the syslinux.com installer. If
541 you are on an WinNT-based system (WinNT, Win2k, WinXP or later), use
542 syslinux.exe instead.
544 1. Make a DOS bootable disk. This can be done either by specifying
545 the /s option when formatting the disk in DOS, or by running the
552 2. Copy the DOS boot sector from the disk into a file. The file
553 *must* have extension .bss:
557 3. Run SYSLINUX on the disk:
561 4. Copy the Linux kernel image(s), initrd(s), etc to the disk, and
562 create/edit syslinux.cfg and help files if desired:
568 ++++ COMBOOT EXECUTABLES ++++
570 SYSLINUX supports simple standalone programs, using a file format
571 similar to DOS ".com" files. A 32-bit version, called COM32, is also
572 provided. A simple API provides access to a limited set of filesystem
573 and console functions.
575 See the file comboot.doc for more information on COMBOOT and COM32
579 ++++ NOVICE PROTECTION ++++
581 SYSLINUX will attempt to detect if the user is trying to boot on a 286
582 or lower class machine, or a machine with less than 608K of low ("DOS")
583 RAM (which means the Linux boot sequence cannot complete). If so, a
584 message is displayed and the boot sequence aborted. Holding down the
585 Ctrl key while booting disables this feature.
587 The compile time and date of a specific SYSLINUX version can be obtained
588 by the DOS command "type ldlinux.sys". This is also used as the
589 signature for the LDLINUX.SYS file, which must match the boot sector.
591 Any file that SYSLINUX uses can be marked hidden, system or readonly if
592 so is convenient; SYSLINUX ignores all file attributes. The SYSLINUX
593 installed automatically sets the readonly attribute on LDLINUX.SYS.
596 ++++ NOTES ON BOOTABLE CD-ROMS ++++
598 SYSLINUX can be used to create bootdisk images for El
599 Torito-compatible bootable CD-ROMs. However, it appears that many
600 BIOSes are very buggy when it comes to booting CD-ROMs. Some users
601 have reported that the following steps are helpful in making a CD-ROM
602 that is bootable on the largest possible number of machines:
604 a) Use the -s (safe, slow and stupid) option to SYSLINUX;
605 b) Put the boot image as close to the beginning of the
606 ISO 9660 filesystem as possible.
608 A CD-ROM is so much faster than a floppy that the -s option shouldn't
609 matter from a speed perspective.
611 Of course, you may want to use ISOLINUX instead. See isolinux.doc.
614 ++++ BOOTING FROM A FAT FILESYSTEM PARTITION ON A HARD DISK ++++
616 SYSLINUX can boot from a FAT12 or FAT16 filesystem partition on a hard
617 disk (FAT32, introduced in Windows 95 OSR-2, is not supported,
618 however.) The installation procedure is identical to the procedure
619 for installing it on a floppy, and should work under either DOS or
620 Linux. To boot from a partition, SYSLINUX needs to be launched from a
621 Master Boot Record or another boot loader, just like DOS itself would.
623 Under DOS, you can install a standard simple MBR on the primary hard
624 disk by running the command:
628 Then use the FDISK command to mark the appropriate partition active.
630 A simple MBR, roughly on par with the one installed by DOS (but
631 unencumbered), is included in the SYSLINUX distribution
636 SYSLINUX is unsafe to use on any filesystem that extends past cylinder
637 1024. This is a fundamental limitation of the standard BIOS API. The
638 "extended" BIOS API can *sometimes* be used to work around it, but
639 there simply is not enough space in the SYSLINUX boot sector to
642 SYSLINUX will not work (and will refuse to install) on filesystems
643 with a cluster size of more than 16K (typically means a filesystem of
647 ++++ HARDWARE INFORMATION +++
649 I have started to maintain a web page of hardware with known
650 problems. There are, unfortunately, lots of broken hardware out
651 there; especially early PXE stacks (for PXELINUX) have lots of
654 A list of problems, and workarounds (if known), is maintained at:
656 http://syslinux.zytor.com/hardware.php
659 ++++ BUG REPORTS ++++
661 I would appreciate hearing of any problems you have with SYSLINUX. I
662 would also like to hear from you if you have successfully used SYSLINUX,
663 *especially* if you are using it for a distribution.
665 If you are reporting problems, please include all possible information
666 about your system and your BIOS; the vast majority of all problems
667 reported turn out to be BIOS or hardware bugs, and I need as much
668 information as possible in order to diagnose the problems.
670 There is a mailing list for discussion among SYSLINUX users and for
671 announcements of new and test versions. To join, or to browse the
674 http://www.zytor.com/mailman/listinfo/syslinux
676 Please DO NOT send HTML messages or attachments to the mailing list
677 (including multipart/alternative or similar.) All such messages will