SYSLINUX

A bootloader for Linux using MS-DOS floppies

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.

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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] [-o offset] /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. If you find a machine on

which the -s option is required to make it boot reliably, please send

as much info about your machine as you can, and include the failure

mode.

The -o option is used with a disk image file and specifies the byte

offset of the filesystem image in the file.

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):

All options here applies to PXELINUX as well as SYSLINUX unless

otherwise noted. See pxelinux.doc for additional information on

PXELINUX.

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.

IPAPPEND flag_val

The IPAPPEND option is available only on PXELINUX, and

indicates (if the flag value is 1) that an option of the

following format should be generated and added:

ip=<client-ip>:<boot-server-ip>:<gw-ip>:<netmask>

... based on the input from the DHCP/BOOTP or PXE boot server.

LABEL label

KERNEL image

APPEND options...

IPAPPEND flag_val

Indicates that if "label" is entered as the kernel to boot,

SYSLINUX should instead boot "image", and the specified APPEND

and IPAPPEND 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"

... whereas SYSLINUX uses the syntax:

label mylabel

kernel mykernel

append myoptions

Notes: Labels are mangled as if they were 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.

LOCALBOOT type

On PXELINUX, specifying "LOCALBOOT 0" instead of a "KERNEL"

option means invoking this particular label will cause a local

disk boot instead of booting a kernel.

The argument 0 means perform a normal boot. The argument 4

will perform a local boot with the Universal Network Driver

Interface (UNDI) driver still resident in memory. Finally,

the argument 5 will perform a local boot with the entire PXE

stack, including the UNDI driver, still resident in memory.

All other values are undefined. If you don't know what the

UNDI or PXE stacks are, don't worry -- you don't want them,

just specify 0.

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.

SERIAL port [baudrate]

Enables a serial port to act as the console. "port" is a

number (0 = /dev/ttyS0 = COM1, etc.); if "baudrate" is

omitted, the baud rate defaults to 9600 bps. The serial

parameters are hardcoded to be 8 bits, no parity, 1 stop bit.

For this directive to be guaranteed to work properly, it

should be the first directive in the configuration file.

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.

When using the serial console, press <Ctrl-F><digit> to get to

the help screens, e.g. <Ctrl-F><2> to get to the F2 screen,

and <Ctrl-F><0> for the F10 one.

In the configuration file 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. PXELINUX identifies using the ID

byte 0x32. The ID range 0x33-0x3f 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.

Colors are not visible over the serial console.

<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 (OR OTHER SIMILAR OPERATING SYSTEMS) ++++

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

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

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