path: root/syslinux.doc

			       SYSLINUX
			     Version 1.35
			    April 13, 1998

              A bootloader for Linux using MS-DOS floppies

		Copyright (C) 1994-1998 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 MS-DOS floppies.  It is intended to simplify first-time
installation of Linux, and for creation of rescue- and other
special-purpose boot floppies.  It is *not* intended to be used as a
general purpose boot loader; once the operating system is installed I
recommend LILO as the boot loader, except for people whose root
filesystem is a UMSDOS filesystem (where a DOS defragmenter could
wreck havoc with LILO's carefully set up block tables) -- for them I
recommend Loadlin (which loads Linux from the DOS command line).

SYSLINUX could, however, in conjunction with the UMSDOS filesystem,
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.

   ++++ 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) 

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 will install a "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 kernel
  APPEND options...
        Indicates that if "label" is entered as the kernel to boot,
        SYSLINUX should instead boot "kernel", 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 "kernel" is the same as "label", and if no
        APPEND is given the default is to use the global entry (if any).
        Up to 16 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

	Note:	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.

  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.

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

   ++++ 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 boottime-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).

   ++++ 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 (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 ++++

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.

SYSLINUX, like DOS, requires that the partition which contains it
lives entirely below cylinder 1024 for proper operation.

   ++++ 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.

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.