path: root/syslinux.doc

			       SYSLINUX
			     Version 1.43
			    March 19, 1999

              A bootloader for Linux using MS-DOS floppies

		Copyright (C) 1994-1999 H. Peter Anvin

This program is provided under the terms of the GNU General Public
License, version 2 or, at your option, any later version.  There is no
warranty, neither expressed nor implied, to the function of this
program.  Please see the included file COPYING for details.

SYSLINUX is a boot loader for the Linux operating system which
operates off an MS-DOS/Windows FAT filesystem.  It is intended to
simplify first-time installation of Linux, and for creation of rescue-
and other special-purpose boot disks.

SYSLINUX can be used, when properly set up, completely eliminate the
need for distribution of raw diskette images for boot floppies.  A
SYSLINUX floppy can be manipulated using standard MS-DOS (or any other
OS that can access an MS-DOS filesystem) tools once it has been
created.

   ++++ WHAT SYSLINUX IS NOT ++++

SYSLINUX is probably not suitable as a general purpose boot loader.
It can only boot Linux from a FAT filesystem, and not, for example,
ext2.  Since a native Linux implementation will typically use ext2,
another boot loader (e.g. LILO) is probably more suitable.  In a
system which actually contains DOS or Windows, LOADLIN may be simpler
to use.

However, SYSLINUX has shown itself to be quite useful in a number of
special-purpose applications.

   ++++ CREATING A BOOTABLE LINUX FLOPPY +++

In order to create a bootable Linux floppy using SYSLINUX, prepare a
normal MS-DOS formatted floppy.  Copy one or more Linux kernel files to
it, then execute the DOS command:

        syslinux [-s] a:

(or whichever drive letter is appropriate; the [] meaning -s is optional) 

or the Linux command:

	syslinux [-s] /dev/fd0

(or, again, whichever device is the correct one.)

This will alter the boot sector on the disk and copy a file named
LDLINUX.SYS into its root directory.

The -s option, if given, will install a "safe, slow and stupid"
version of SYSLINUX.  This version may work on some very buggy BIOSes
on which SYSLINUX would otherwise fail.

WARNING: There seems to be a bug in some recent experimental Linux
	 kernels that causes floppy disk corruption when using the
	 Linux syslinux installer.  This bug exists in kernels
	 2.1.79-2.1.86; as far as I know the bug is fixed in 2.1.87.

On boot time, by default, the kernel will be loaded from the image named
LINUX on the boot floppy.  This default can be changed, see the section
on the SYSLINUX config file.

If the Shift or Alt keys are held down during boot, or the Caps or Scroll
locks are set, SYSLINUX will display a LILO-style "boot:" prompt.  The
user can then type a kernel file name followed by any kernel parameters.
The SYSLINUX loader does not need to know about the kernel file in
advance; all that is required is that it is a file located in the root
directory on the disk.

   ++++ CONFIGURATION FILE ++++

All the configurable defaults in SYSLINUX can be changed by putting a
file called SYSLINUX.CFG in the root directory of the boot floppy.  This
is a text file in either UNIX or DOS format, containing one or more of
the following items (case is insensitive for keywords; upper case is used
here to indicate that a word should be typed verbatim):

DEFAULT kernel options...
        Sets the default command line.  If SYSLINUX boots automatically,
        it will act just as if the entries after DEFAULT had been typed
        in at the "boot:" prompt, except that the option "auto" is
        automatically added, indicating an automatic boot.

        If no configuration file is present, or no DEFAULT entry is
        present in the config file, the default is kernel name "linux",
        with no options.

APPEND options...
        Add one or more options to the kernel command line.  These are
        added both for automatic and manual boots.  The options are
        added at the very beginning of the kernel command line,
        usually permitting explicitly entered kernel options to override
        them.  This is the equivalent of the LILO "append" option.

LABEL label
  KERNEL image
  APPEND options...
        Indicates that if "label" is entered as the kernel to boot,
        SYSLINUX should instead boot "image", and the specified APPEND
        options should be used instead of the ones specified in the
        global section of the file (before the first LABEL command.)
        The default for "image" is the same as "label", and if no
        APPEND is given the default is to use the global entry (if any).
        Up to 128 LABEL entries are permitted.

        Note that LILO uses the syntax:
        image = mykernel
          label = mylabel
          append = "myoptions"

        corresponding to the SYSLINUX:
        label mylabel
          kernel mykernel
          append myoptions

	Notes:	Labels are mangled as if they were DOS filenames, and must be
		unique after mangling.  For example, two labels
		"v2.1.30" and "v2.1.31" will not be distinguishable.

		The "image" doesn't have to be a Linux kernel; it can
		be a boot sector or a COMBOOT file (see below.)

  APPEND -
        Append nothing.  APPEND with a single hyphen as argument in a
        LABEL section can be used to override a global APPEND.

IMPLICIT flag_val
        If flag_val is 0, do not load a kernel image unless it has been
        explicitly named in a LABEL statement.  The default is 1.

TIMEOUT timeout
        Indicates how long to wait at the boot: prompt until booting
        automatically, in units of 1/10 s.  The timeout is cancelled as
        soon as the user types anything on the keyboard, the assumption
        being that the user will complete the command line already
        begun.  A timeout of zero will disable the timeout completely,
        this is also the default.

        NOTE: The maximum possible timeout value is 35996; corresponding to
        just below one hour.

FONT filename
	Load a font in .psf format before displaying any output
	(except the copyright line, which is output as ldlinux.sys
	itself is loaded.)  SYSLINUX only loads the font onto the
	video card; if the .psf file contains a Unicode table it is
	ignored.  This only works on EGA and VGA cards; hopefully it
	should do nothing on others.

KBDMAP keymap
	Install a simple keyboard map.  The keyboard remapper used is
	*very* simplistic (it simply remaps the keycodes received from
	the BIOS, which means that only the key combinations relevant
	in the default layout -- usually U.S. English -- can be
	mapped) but should at least help people with AZERTY keyboard
	layout and the locations of = and , (two special characters
	used heavily on the Linux kernel command line.)

	The included program keytab-lilo.pl from the LILO distribution
	can be used to create such keymaps.  The file keytab-lilo.doc
	contains the documentation for this program.

DISPLAY filename
        Displays the indicated file on the screen at boot time (before
        the boot: prompt, if displayed).  This option takes the place of
        the LINUXMSG.TXT and BOOTMSG.TXT files in SYSLINUX 1.0.  Please
        see the section below on DISPLAY files.

        NOTE: If the file is missing, this option is simply ignored.

PROMPT flag_val
        If flag_val is 0, display the boot: prompt only if the Shift or Alt
        key is pressed, or Caps Lock or Scroll lock is set (this is the
        default).  If flag_val is 1, always display the boot: prompt.  This
        option takes the place of testing for the LINUXMSG.TXT file in
        SYSLINUX 1.0.

F1 filename
F2 filename
   ...etc...
F9 filename
F0 filename
        Displays the indicated file on the screen when a function key is
        pressed at the boot: prompt.  This can be used to implement
        pre-boot online help (presumably for the kernel command line
        options.)  Note that F10 MUST be entered in the config file as
        "F0", not "F10", and that there is currently no way to bind
        file names to F11 and F12.  Please see the section below on
        DISPLAY files.

Blank lines, and comment lines beginning with a hash mark (#) are ignored.

Note that the configuration file is not completely decoded.  Syntax
different from the one described above may still work correctly in this
version of SYSLINUX, but may break in a future one.

   ++++ LARGE KERNELS AND INITIAL RAMDISK SUPPORT ++++

This version of SYSLINUX supports large kernels (bzImage format),
eliminating the 500K size limit of the zImage kernel format.  bzImage
format kernels are detected automatically and handled transparently to
the user.

This version of SYSLINUX also supports a boot-time-loaded ramdisk
(initrd).  An initrd is loaded from a DOS file if the option
"initrd=filename" (where filename is the filename of the initrd image;
the file must be located in the root directory on the boot floppy) is
present on the processed command line (after APPEND's have been added,
etc.).  If several initrd options are present, the last one has
precedence; this permits user-entered options to override a config
file APPEND.  Specifying "initrd=" without a filename inhibits initrd
loading.  The file specified by the initrd= option will typically be a
gzipped filesystem image.

NOTE: One of the main advantages with SYSLINUX is that it makes it
very easy to support users with new or unexpected configurations,
especially in a distribution setting.  If initrd is used to
extensively modularize the distribution kernel, it is strongly
recommended that a simple way of adding drivers to the boot floppy be
provided.  The suggested manner is to let the initrd system mount the
boot floppy and look for additional drivers in a predetermined
location.

To bzImage and recent zImage kernels, SYSLINUX 1.30 and higher will
identify using the ID byte 0x31.  The ID range 0x32-0x3f is reserved
for future versions of SYSLINUX.

   ++++ DISPLAY FILE FORMAT ++++

DISPLAY and function-key help files are text files in either DOS or UNIX
format (with or without <CR>).  In addition, the following special codes
are interpreted:

<FF>                                    <FF> = <Ctrl-L> = ASCII 12
        Clear the screen, home the cursor.  Note that the screen is
        filled with the current display color.

<SI><bg><fg>                            <SI> = <Ctrl-O> = ASCII 15
        Set the display colors to the specified background and
        foreground colors, where <bg> and <fg> are hex digits,
        corresponding to the standard PC display attributes:

        0 = black               8 = dark grey
        1 = dark blue           9 = bright blue
        2 = dark green          a = bright green
        3 = dark cyan           b = bright cyan
        4 = dark red            c = bright red
        5 = dark purple         d = bright purple
        6 = brown               e = yellow
        7 = light grey          f = white

        Picking a bright color (8-f) for the background results in the
        corresponding dark color (0-7), with the foreground flashing.

<SUB>                                   <SUB> = <Ctrl-Z> = ASCII 26
        End of file (DOS convention).

   ++++ COMBOOT IMAGES AND OTHER OPERATING SYSTEMS ++++

This version of SYSLINUX supports chain loading of other operating
systems (such as MS-DOS and its derivatives, including Windows 95/98),
as well as COMBOOT-style standalone executables (a subset of DOS .COM
files; see separate section below.)

Chain loading requires the boot sector of the foreign operating system
to be stored in a file in the root directory of the filesystem.
Because neither Linux kernels, boot sector images, nor COMBOOT files
have reliable magic numbers, SYSLINUX will look at the file
extension.  The following extensions are recognized:

	none or other	Linux kernel image
	.CBT		COMBOOT image (not runnable from DOS)
	.BSS		Boot sector (DOS superblock will be patched in)
	.BS		Boot sector
	.COM		COMBOOT image (runnable from DOS)

For filenames given on the command line, SYSLINUX will search for the
file by adding extensions in the order listed above if the plain
filename is not found.  Filenames in KERNEL statements must be fully
qualified.

   ++++ BOOTING DOS ++++

This is the recommended procedure for creating a SYSLINUX disk that
can boot either DOS or Linux.  This example assumes the drive is A: in
DOS and /dev/fd0 in Linux; for other drives, substitute the
appropriate drive designator.

   ---- Linux procedure ----

1. Make a DOS bootable disk.  This can be done either by specifying
   the /s option when formatting the disk in DOS, or by running the
   DOS command SYS (this can be done under DOSEMU if DOSEMU has
   direct device access to the relevant drive):

	format a: /s
   or
	sys a:

2. Boot Linux.  Copy the DOS boot sector from the disk into a file:

	dd if=/dev/fd0 of=dos.bss bs=512 count=1

3. Run SYSLINUX on the disk:

	syslinux /dev/fd0

4. Mount the disk and copy the DOS boot sector file to it.  The file
   *must* have extension .bss:

	mount -t msdos /dev/fd0 /mnt
	cp dos.bss /mnt

5. Copy the Linux kernel image(s), initrd(s), etc to the disk, and
   create/edit syslinux.cfg and help files if desired:

	cp vmlinux /mnt
	cp initrd.gz /mnt

6. Unmount the disk (if applicable.)

	umount /mnt
 
   ---- DOS procedure ----

To make this installation in DOS only, you need the utility copybs.com
(included with SYSLINUX) as well as the syslinux.com installer.

1. Make a DOS bootable disk.  This can be done either by specifying
   the /s option when formatting the disk in DOS, or by running the
   DOS command SYS:

	format a: /s
   or
	sys a:

2. Copy the DOS boot sector from the disk into a file.  The file
   *must* have extension .bss:

	copybs a: a:dos.bss

3. Run SYSLINUX on the disk:

	syslinux a:

4. Copy the Linux kernel image(s), initrd(s), etc to the disk, and
   create/edit syslinux.cfg and help files if desired:

	copy vmlinux a:
	copy initrd.gz a:
 
   ++++ COMBOOT EXECUTABLES ++++

A COMBOOT file is a standalone executable in DOS .COM format.  They
can, among other things, be produced by the Etherboot package by
Markus Gutschke and Ken Yap.  The following requirements apply for
these files to be sufficiently "standalone" for SYSLINUX to be able to
load and run them:

  * The program must not execute any DOS calls (since there is no
    DOS), although it may call the BIOS.  The only exception is that
    the program may execute INT 20h (Terminate Program) to return to
    the SYSLINUX prompt.  Note especially that INT 21h AH=4Ch, INT 21h
    AH=31h or INT 27h are *not* supported.
  * Only the following fields in the PSP are supported:
    - pspInt20 at offset 00h;
    - pspNextParagraph at offset 02h;
    - pspCommandTail at offset 80h (contains the arguments from the
      SYSLINUX command line).

    All other fields will contain zero.
  * The program must not modify any main memory outside its 64K
    segment if it returns to SYSLINUX via INT 20h.

SYSLINUX requires that COMBOOT files end in ".COM" or ".CBT".  Files
ending in .COM can be run from the DOS command line, files ending in
.CBT cannot, otherwise there is no difference.  SYSLINUX will prefer a
.CBT file over a similarly named .COM.

SYSLINUX currently doesn't provide any form of API for the use of
COMBOOT files.  If there is need, a future version may contain an INT
interface to some SYSLINUX functions; please contact me if you have a
need or ideas for such an API.

   ++++ NOVICE PROTECTION ++++

SYSLINUX will attempt to detect if the user is trying to boot on a 286
or lower class machine, or a machine with less than 608K of low ("DOS")
RAM (which means the Linux boot sequence cannot complete).  If so, a
message is displayed and the boot sequence aborted.  Holding down the
Ctrl key while booting disables this feature.

The compile time and date of a specific SYSLINUX version can be obtained
by the DOS command "type ldlinux.sys".  This is also used as the
signature for the LDLINUX.SYS file, which must match the boot sector.

Any file that SYSLINUX uses can be marked hidden, system or readonly if
so is convenient; SYSLINUX ignores all file attributes.  The SYSLINUX
installed automatically sets the readonly attribute on LDLINUX.SYS.

   ++++ NOTES ON BOOTABLE CD-ROMS ++++

SYSLINUX can be used to create bootdisk images for El
Torito-compatible bootable CD-ROMs.  However, it appears that many
BIOSes are very buggy when it comes to booting CD-ROMs.  Some users
have reported that the following steps are helpful in making a CD-ROM
that is bootable on the largest possible number of machines:

	a) Use the -s (safe, slow and stupid) option to SYSLINUX;
	b) Put the boot image as close to the beginning of the
	   ISO 9660 filesystem as possible.

A CD-ROM is so much faster than a floppy that the -s option shouldn't
matter from a speed perspective.

   ++++ BOOTING FROM A FAT FILESYSTEM PARTITION ON A HARD DISK ++++

SYSLINUX can boot from a FAT12 or FAT16 filesystem partition on a hard
disk (FAT32, introduced in Windows 95 OSR-2, is not supported,
however.)  The installation procedure is identical to the procedure
for installing it on a floppy, and should work under either DOS or
Linux.  To boot from a partition, SYSLINUX needs to be launched from a
Master Boot Record or another boot loader, just like DOS itself would.

Under DOS, you can install a standard simple MBR on the primary hard
disk by running the command:

	FDISK /MBR

Then use the FDISK command to mark the appropriate partition active.

   ++++ KNOWN BUGS ++++

SYSLINUX is unsafe to use on any filesystem that extends past cylinder
1024.  This is a fundamental limitation of the standard BIOS API.

SYSLINUX will not work (and will refuse to install) on filesystems
with a cluster size of more than 16K (typically means a filesystem of
more than 1 GB.)

   ++++ COMPATIBILITY WITH SYSLINUX 1.0 ++++

The following combinations of options can be used to mimic the behaviour
of SYSLINUX 1.0 with LINUXMSG.TXT or BOOTMSG.TXT present, respectively:

# Mimic SYSLINUX 1.0 with LINUXMSG.TXT file present:
display linuxmsg.txt
prompt 1

# Mimic SYSLINUX 1.0 with BOOTMSG.TXT file present:
display bootmsg.txt

   ++++ BUG REPORTS ++++

I would appreciate hearing of any problems you have with SYSLINUX.  I
would also like to hear from you if you have successfully used SYSLINUX,
*especially* if you are using it for a distribution.

If you are reporting problems, please include all possible information
about your system and your BIOS; the vast majority of all problems
reported turn out to be BIOS or hardware bugs, and I need as much
information as possible in order to diagnose the problems.

There is a mailing list for discussion among SYSLINUX users and for
announcements of new and test versions.  To join, send a message to
majordomo@linux.kernel.org with the line:

subscribe syslinux

in the body of the message.  The submission address is
syslinux@linux.kernel.org.