Section: User Commands (1)
Updated: 18 December 2007
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syslinux - install the SYSLINUX bootloader on a FAT filesystem
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.
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
-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.
Syslinux supports the loading of initial ramdisks (initrd) and the
bzImage kernel format.
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.
Force install even if it appears unsafe.
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 booting.
- -d subdirectory
Install the SYSLINUX control files in a subdirectory with the
specified name (relative to the root directory on the device).
- -o offset
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
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 permitting explicitly entered kernel options
to override them. This is the equivalent of the
- 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).
Use "append -" to use no options at all. Up to 128 "label" entries are
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
The "image" doesn't have to be a Linux kernel; it can be a boot sector or a
COMBOOT file (see below.)
- 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. 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
- 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
distribution can be used to create such keymaps.
- 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. 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.
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.)
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. For
f10-f12, hit <Ctrl-F>A, <Ctrl-F>B, <Ctrl-F>C. For
compatiblity 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 <CR>). In addition, the following special codes
- <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
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.
- <CAN>filename<newline>, <CAN> = <Ctrl-X> = ASCII 24
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
"ppmtolss16" can be used to produce these images. This Perl
program also includes the file format specification.
The image is displayed in 640x480 16-color mode. Once in
graphics mode, the display attributes (set by <SI> code
sequences) 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 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.
- <EM>, <EM> = <Ctrl-U> = ASCII 25
If we are currently in graphics mode, return to text mode.
- <DLE>..<ETB>, <Ctrl-P>..<Ctrl-W> = ASCII 16-23
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
Character Text Graph Serial
<DLE> = <Ctrl-P> = ASCII 16 No No No
<DC1> = <Ctrl-Q> = ASCII 17 Yes No No
<DC2> = <Ctrl-R> = ASCII 18 No Yes No
<DC3> = <Ctrl-S> = ASCII 19 Yes Yes No
<DC4> = <Ctrl-T> = ASCII 20 No No Yes
<NAK> = <Ctrl-U> = ASCII 21 Yes No Yes
<SYN> = <Ctrl-V> = ASCII 22 No Yes Yes
<ETB> = <Ctrl-W> = ASCII 23 Yes Yes Yes
<DC1>Text mode<DC2>Graphics mode<DC4>Serial port<ETB>
... will actually print out which mode the console is in!
- <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 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
filename is not found. Filenames in KERNEL statements must be fully
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 fields pspInt20 at offset 00h, pspNextParagraph at offset 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 segment if it
returns to syslinux via INT 20h.
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.
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.
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
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
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. 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 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
firstname.lastname@example.org with the line:
in the body of the message. The submission address is email@example.com.
This manual page is a modified version of the original syslinux
documentation by H. Peter Anvin <firstname.lastname@example.org>. The conversion to a manpage
was made by Arthur Korn <email@example.com>.
- Configuration file
- Display file format
- Comboot Images and other operating systems
- Novice protection
- Bootable CD-ROMs
- Booting from a FAT partition on a hard disk
- SEE ALSO
linux.jgfs.net manual pages