syslinux – install the SYSLINUX bootloader on a FAT filesystem
syslinux [-sfr] [-d directory] [-o offset] device
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 spe‐
cial-purpose boot disks.
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 command:
This will alter the boot sector on the disk and copy a file named
LDLINUX.SYS into its root directory.
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 configuration 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(8) -style “boot:”
prompt. The user can then type a kernel file name followed by any ker‐
nel 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.
Syslinux supports the loading of initial ramdisks (initrd) and the
bzImage kernel format.
-s Install a “safe, slow and stupid” version of syslinux. This ver‐
sion 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.
-f Force install even if it appears unsafe.
-r RAID mode. If boot fails, tell the BIOS to boot the next device
in the boot sequence (usually the next hard disk) instead of
stopping with an error message. This is useful for RAID-1 boot‐
Install the SYSLINUX control files in a subdirectory with the
specified name (relative to the root directory on the device).
Indicates that the filesystem is at an offset from the base of
the device or 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).
In the configuration file blank lines and comment lines beginning with
a hash mark (#) are ignored.
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.
If no configuration file is present, or no “default” entry is
present in the configuration file, the default is “linux auto”.
NOTE: Earlier versions of SYSLINUX used to automatically
append the string “auto” to whatever the user specified using
the DEFAULT command. As of version 1.54, this is no longer
true, as it caused problems when using a shell as a substitute
for “init.” You may want to include this option manually.
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 per‐
mitting explicitly entered kernel options to override them. This
is the equivalent of the lilo(8)
append options …
Indicates that if label is entered as the kernel to boot, sys‐
linux 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). Use
“append -” to use no options at all. Up to 128 “label” entries
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.)
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.
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. 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 hard‐
coded 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.
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
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(8) from the lilo(8)
distribution can be used to create such keymaps.
Displays the indicated file on the screen at boot time (before
the boot: prompt, if displayed). Please see the section below on
DISPLAY files. If the file is missing, this option is simply
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:”
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
When using the serial console, press
the help screens, e.g.
with earlier versions, f10 can also be entered as
Display file format
DISPLAY and function-key help files are text files in either DOS or
UNIX format (with or without
codes are interpreted:
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 fore‐
ground colors, where
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.
If a VGA display is present, enter graphics mode and display the
graphic included in the specified file. The file format is an
ad hoc format called LSS16; the included Perl program “ppm‐
tolss16” can be used to produce these images. This Perl program
also includes the file format specification.
The image is displayed in 640×480 16-color mode. Once in graph‐
ics mode, the display attributes (set by
work slightly differently: the background color is ignored, and
the foreground colors are the 16 colors specified in the image
file. For that reason, ppmtolss16 allows you to specify that
certain colors should be assigned to specific color indicies.
Color indicies 0 and 7, in particular, should be chosen with
care: 0 is the background color, and 7 is the color used for the
text printed by SYSLINUX itself.
If we are currently in graphics mode, return to text mode.
These codes can be used to select which modes to print a certain
part of the message file in. Each of these control characters
select a specific set of modes (text screen, graphics screen,
serial port) for which the output is actually displayed:
Character Text Graph Serial
… will actually print out which mode the console is in!
End of file (DOS convention).
Comboot Images and other operating systems
This version of syslinux supports chain loading of other operating sys‐
tems (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 recognised:
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 file‐
name is not found. Filenames in KERNEL statements must be fully quali‐
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
· 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 fields pspInt20 at offset 00h, pspNextParagraph at off‐
set 02h and pspCommandTail at offset 80h (contains the arguments
from the syslinux command line) in the PSP are supported. All
other fields will contain zero.
· The program must not modify any main memory outside its 64K seg‐
ment if it returns to syslinux via INT 20h.
Syslinux currently doesn’t provide any form of API for the use of COM‐
BOOT 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.
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 sec‐
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.
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:
· Use the -s (safe, slow and stupid) option to SYSLINUX
· 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.
Of course, you probably want to use ISOLINUX instead. See the documen‐
tation file isolinux.doc.
Booting from a FAT partition on a hard disk
SYSLINUX can boot from a FAT filesystem partition on a hard disk
(including FAT32). The installation procedure is identical to the pro‐
cedure 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. A sample master boot sector (mbr.bin) is included with SYSLINUX.
I would appreciate hearing of any problems you have with SYSLINUX. I
would also like to hear from you if you have successfully used SYS‐
LINUX, 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
firstname.lastname@example.org with the line:
in the body of the message. The submission address is sys‐
lilo(8), keytab-lilo.pl(8), fdisk(8), mkfs(8), superformat(1).
This manual page is a modified version of the original syslinux docu‐
mentation by H. Peter Anvin
page was made by Arthur Korn
SYSLINUX 18 December 2007 SYSLINUX