Difference between revisions of "SYSLINUX"

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COM32 program (.c32)
COM32 program (.c32)
====CONFIG image ====
====CONFIG file ====
CONFIG will restart the boot loader using a different configuration file.
CONFIG will restart the boot loader using a different configuration file.
Load new config file:
LABEL new_config
CONFIG </path/to/cfg/file>/<configfile.cfg>
Set Syslinux' home dir to </path/to/cfg/file> and load new config file:
LABEL new_config2
CONFIG </path/to/cfg/file>/<configfile.cfg> </path/to/cfg/file>
===APPEND options... ===
===APPEND options... ===

Revision as of 06:55, 19 April 2011

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These are the options common to all versions of the SYSLINUX installer:

	-s	Safe, slow, stupid: uses simpler code that boots better. 
		  If you find a machine on which the -s option is required to make it boot reliably, 
	-f	Force installing.
	-r	Raid mode:
		  (usually the next hard disk), instead of stopping with an error message.
		  This is useful for RAID-1 booting.

These are only available in the Windows version:

	-m	MBR: install a bootable MBR sector to the beginning of the drive.
	-a	Active: marks the partition used active (=bootable)

This is can only be used in the linux version:

	-o      Specifies the byte offset of the filesystem image in the file.
		  It has to be used with a disk image file.

Creating a Bootable Disk

Installing SYSLINUX will alter the boot sector on the disk, and copy a file named LDLINUX.SYS into the root directory.

At boot time, by default, the kernel will be loaded from the image named LINUX on the boot disk. 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 a file in the root directory of the disk.

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


syslinux.exe [-sfmar][-d directory] <drive>: [bootsecfile]
Floppy: (a: in this example)
syslinux.exe a:
HardDrive/FlashDrive/etc: (z: in this example)
syslinux.exe -m -a -d /boot/syslinux z:
* In the above example syslinux.cfg would be expected to be in z:\boot\syslinux
* NOTE: Under NT/2K you may get a dialog box about not getting exclusive access and with Abort/Retry/Ignore buttons; selecting "Ignore" will make the command execute sucessfully.


syslinux.com [-sfmar][-d directory] <drive>: [bootsecfile]
syslinux.com a:


syslinux [-sfr][-d directory][-o offset] <DeviceOrImage>
syslinux /dev/fd0

The -o option (if specified) is used with a disk image file and specifies the byte offset of the filesystem image in the file.

How do I Configure SYSLINUX?

All the configurable defaults in SYSLINUX can be changed by creating a file called syslinux.cfg.

SYSLINUX searches for the SYSLINUX.CFG file in the following order:


All filenames inside the config file are assumed to be relative to the directory SYSLINUX.CFG is in, unless preceded with a slash or backslash.


Here is a simple example syslinux.cfg file, with one entry to boot a Linux kernel:

LABEL linux
  SAY Now booting the kernel from SYSLINUX...
  KERNEL vmlinuz.img
  APPEND ro root=/dev/sda1 initrd=initrd.img

Note that LILO uses the syntax:

image = mykernel
  label = mylabel
  append = "myoptions"

... whereas SYSLINUX uses the syntax:

LABEL mylabel
  KERNEL mykernel
  APPEND myoptions

All options here apply to PXELINUX, ISOLINUX and EXTLINUX as well as SYSLINUX unless otherwise noted.

INCLUDE filename

Inserts the contents of another file at this point in the configuration file. Currently, files can be nested up to 16 levels deep, but it is not guaranteed that more than 8 levels will be supported in future versions.

LABEL command

A human-readable string that describes a kernel and options. The default LABEL is "linux", but you can change this with the "DEFAULT" keyword.

Labels are mangled as if they were filenames, and must be unique after mangling. For example, the labels "v2.1.30" and "v2.1.31" will not be distinguishable under SYSLINUX, since both mangle to the same DOS filename.


Selects the file SYSLINUX will boot. The "kernel" doesn't have to be a Linux kernel, it can be a boot sector or a COMBOOT file.

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 kernel boot sector images, nor COMBOOT files have reliable magic numbers, Syslinux will look at the file extension. The following extensions are recognized (case insensitive):

 none or other	Linux kernel image
 .0		PXE bootstrap program (NBP) [PXELINUX only]
 .bin		"CD boot sector" [ISOLINUX only]
 .bs		Boot sector [SYSLINUX only]
 .c32		COM32 image (32-bit COMBOOT)
 .cbt		COMBOOT image (not runnable from DOS)
 .com		COMBOOT image (runnable from DOS)
 .img		Disk image [ISOLINUX only]

Using one of these keywords instead of KERNEL forces the filetype, regardless of the filename:

LINUX image

You can use this, instead of using KERNEL file to boot a linux kernel image.

BOOT image

Bootstrap program (.bs, .bin)

BSS image

BSS image (.bss)

PXE image

PXE Network Bootstrap Program (.0)


Floppy disk image (.img)


COMBOOT program (.com, .cbt)

COM32 image

COM32 program (.c32)


CONFIG will restart the boot loader using a different configuration file.

Load new config file:

LABEL new_config


LABEL new_config2

APPEND options...

Adds one or more options to the kernel command line. These are added to both 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.

The entire APPEND statement must be on a single line. A feature to break up a long line into multiple lines will be added eventually.

If you enter multiple APPEND statements in a single menu entry, only the last one will be used.



IPAPPEND flag_val [PXELINUX only]

The IPAPPEND option is available only on PXELINUX. The flag_val is an OR of the following options:

1: indicates that an option of the following format should be generated and added to the kernel command line:



The use of this option is not recommended. If you have to use it, it is probably an indication that your network configuration is broken. Using just ip=dhcp on the kernel command line is a preferrable option, or, better yet, run dhcpcd/dhclient, from an initrd if necessary.



... in dash-separated hexadecimal with leading hardware type (same as for the configuration file; see PXELINUX documentation).

This allows an initrd program to determine which interface the system booted from.

LABEL label 
KERNEL image
  APPEND options...
  IPAPPEND flag_val [PXELINUX only] 






INITRD initrd_file

Starting with version 3.71, an initrd can be specified in a separate statement (INITRD) instead of as part of the APPEND statement. This functionally appends "initrd=initrd_file" to the kernel command line.

It supports multiple filenames separated by commas. This is mostly useful for initramfs, which can be composed of multiple separate cpio or cpio.gz archives. Note: all files except the last one are zero-padded to a 4K page boundary. This should not affect initramfs.

DEFAULT command

Sets the default command line. If SYSLINUX boots automatically, it will act 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 kernel name is "linux", with no options.

UI module options...


PROMPT flag_val


NOESCAPE flag_val



If flag_val is set to 1, the Tab key does not display labels at the boot: prompt.

IMPLICIT flag_val




TIMEOUT timeout

Indicates how long to pause at the boot: prompt until booting automatically, in units of 1/10 s. The timeout is cancelled when any key is pressed, the assumption being the user will complete the command line. A timeout of zero will disable the timeout completely. The default is 0.

NOTE: The maximum possible timeout value is 35996. (Just under an hour.)


Indicates how long to wait until booting automatically, in units of 1/10 s. This timeout is *not* cancelled by user input, and can thus be used to deal with serial port glitches or "the user walked away" type situations. A timeout of zero will disable the timeout completely. The default is 0.

Both TIMEOUT and TOTALTIMEOUT can be used together, for example:

# Wait 5 seconds unless the user types something, but
# always boot after 15 minutes.

ONTIMEOUT kernel options...

Sets the command line invoked on a timeout. Normally this is the same thing invoked by DEFAULT. If this is specified, then DEFAULT is used only if the user presses <Enter> to boot.

ONERROR kernel options...

If a kernel image is not found (either it doesn't exist, or IMPLICIT is set), run the specified command. The faulty command line is appended to the specified options, so if the ONERROR directive reads:

ONERROR xyzzy plugh 

... and the command line entered by the user is:

foo bar baz 

... SYSLINUX will execute the following as if it were entered by the user:

xyzzy plugh foo bar baz

SERIAL port [[baudrate] flowcontrol]

Enables a serial port to act as the console. "port" is a number (0 = /dev/ttyS0 = COM1, etc.) or an I/O port address (e.g. 0x3F8). If "baudrate" is omitted, the baud rate defaults to 9600 bps. The serial parameters are hardcoded to 8 bits, no parity and 1 stop bit.

"flowcontrol" is a combination of the following bits:

0x001 - Assert DTR
0x002 - Assert RTS
0x010 - Wait for CTS assertion
0x020 - Wait for DSR assertion
0x040 - Wait for RI assertion
0x080 - Wait for DCD assertion
0x100 - Ignore input unless CTS asserted
0x200 - Ignore input unless DSR asserted
0x400 - Ignore input unless RI asserted
0x800 - Ignore input unless DCD asserted

All other bits are reserved.

Typical values are:

    0 - No flow control (default)
0x303 - Null modem cable detect
0x013 - RTS/CTS flow control
0x813 - RTS/CTS flow control, modem input
0x023 - DTR/DSR flow control
0x083 - DTR/DCD flow control

For the SERIAL directive to work properly, it must be the first directive in the configuration file.

NOTE: "port" values from 0 to 3 mean the first four serial ports detected by the BIOS. They may or may not correspond to the legacy port values 0x3F8, 0x2F8, 0x3E8, 0x2E8.

CONSOLE flag_val

If flag_val is 0, disable output to the normal video console. If flag_val is 1, enable output to the video console (this is the default.) Some BIOSes try to forward this to the serial console which can make a total mess of things, so this option lets you disable the video console on these systems.

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 does nothing on others.

KBDMAP keymap


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.

Syslinux also ships a comboot module named kbdmap.c32 which allows changing the keyboard mapping on the fly, making it possible to add a keyboard-selection menu and/or keyboard-selection labels from within the syslinux config file.

SAY message

Prints the message on the screen.

DISPLAY filename

Displays the indicated file on the screen at boot time (before the boot: prompt, if displayed). Please see the section below on DISPLAY files.

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

F[1-12] filename

F1 filename
F2 filename
F9 filename
F10 filename
F11 filename
F12 filename 


Please see the section below on DISPLAY files.


<Ctrl-F><1>			to get the F1 screen
<Ctrl-F><2>			to get the F2 screen
<Ctrl-F><9>			to get the F9 screen
<Ctrl-F><A> (or <Ctrl-F><0>)	to get the F10 screen
<Ctrl-F><B>			to get the F11 screen
<Ctrl-F><C>			to get the F12 screen

In the configuration file, blank lines and comment lines beginning with a hash mark (#) are ignored.


Is There A Way To Define Constants Or Variables?

At present, there is no way to define constants or variables in the configuration file. That feature will be added eventually.

Can SYSLINUX Handle Large Kernels?



EXAMPLE (extlinux):

 APPEND ro root=/dev/hda1 initrd=/boot/initrd.img


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, ISOLINUX 0x33, and EXTLINUX 0x34. The ID range 0x35-0x3f is reserved for future versions of derivatives of SYSLINUX.

What is the DISPLAY File Format?


Clear the screen, home the cursor:


Note that the screen is filled with the current display color.

Set the display colors to the specified background and foreground colors:



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


Colors are not visible over the serial console.

Example: color.txt file:

^O9eBlinking Yellow on Blue Background
# xxd color.txt
0000000: 0f39 6542 6c69 6e6b 696e 6720 5965 6c6c  .9eBlinking Yell
0000010: 6f77 206f 6e20 426c 7565 2042 6163 6b67  ow on Blue Backg
0000020: 726f 756e 640a                           round.

Display graphic from filename:





Return to text mode:


If we are currently in graphics mode, return to text mode. Select to which modes to print a certain part of the message:



Character                       Text    Graph   Serial

For example:


will actually print out which mode the console is in!

End of file:


End of file (DOS convention).



Beep the speaker.

Write DISPLAY file with IsoLinux Mate

IsoLinux Mate (ILM) is a Windows 32-bit executable that makes it easier to write a DISPLAY file.

With ILM you can insert color commands, insert ASCII graphics with "not a real on-screen keyboard", preview your work, ...