4 :author: H. Peter Anvin
5 :author-email: hpa@zytor.com
7 :editor1-email: gene.cumm@gmail.com
8 :editor1-revlast: 2012-10-28
9 :nbsp8:         
10 :nbsp32: {nbsp8}{nbsp8}{nbsp8}{nbsp8}
14 syslinux.cfg - *Syslinux* configuration file
18 Configuration for the boot behavior and user experience of *Syslinux*
19 boot loaders, the format of display files and the boot prompt behavior.
21 Blank lines are ignored.
23 Note that the configuration file is not completely decoded. Syntax
24 different from the one described above may still work correctly in this
25 version of *Syslinux*, but may break in a future one.
29 *SYSLINUX* (before 4.00) used the configuration filename of
30 syslinux.cfg. *EXTLINUX* (merged into *SYSLINUX* as of 4.00) used the
31 filename extlinux.conf. Both default to searching for the config file
32 in the installed directory (containing ldlinux.sys/extlinux.sys). As of
33 4.00, *SYSLINUX* will search for extlinux.conf then syslinux.cfg in each
34 directory before falling back to the next directory.
36 As of 3.35, *SYSLINUX* also searches /boot/syslinux, /syslinux and /.
38 *ISOLINUX* (before 4.02) used the configuration filename of
39 isolinux.cfg, searching /boot/isolinux (starting 2.00), then /isolinux
40 and /. As of 4.02, *ISOLINUX* will search for isolinux.cfg then
41 syslinux.cfg in /boot/isolinux before searching for the same files in
42 /isolinux, /boot/syslinux, /syslinux, and /.
45 == GLOBAL DIRECTIVES - MAIN ==
47 A line comment. As of version 3.10, the space between the *#* and the
48 comment is no longer required.
51 (3.00+) A directive for the simple menu system, treated as a comment
52 outside the menu. See menu.txt.
54 *INCLUDE* 'filename'::
55 Inserts the contents of another file at this point in the configuration
56 file. Files can currently be nested up to 16 levels deep, but it is not
57 guaranteed that more than 8 levels will be supported in the future.
59 *DEFAULT* 'kernel' 'options...'::
60 Sets the default command line (which often references a LABEL). If
61 *Syslinux* boots automatically, it will act just as if the entries after
62 *DEFAULT* had been typed in at the 'boot:' prompt. Multiple uses will
63 result in an override.
65 If no configuration file is present, or no *DEFAULT* or *UI* entry is
66 present in the config file, an error message is displayed and the
67 'boot:' prompt is shown (3.85+).
69 *UI* 'module' 'options...'::
70 Selects a specific user interface 'module' (typically menu.c32 or
71 vesamenu.c32). The command-line interface treats this as a directive
72 that overrides the *DEFAULT* directive to load this module instead at
73 startup, for an empty command line and at timeout and *PROMPT* directive
74 to not prompt (but these directives may have effects on other
75 configuration parsers). Multiple uses will result in an override.
78 Begin a new *LABEL* clause. If 'mylabel' is entered as the kernel to
79 boot, *Syslinux* should instead boot "image" (specified by a directive
80 from *KERNEL-LIKE DIRECTIVES*) with any specified *DUAL-PURPOSE
81 DIRECTIVES* being used instead of the global instance.
83 'mylabel' must be unique. Currently the first instance is used but may
84 result in an error or undesired behavior. 'mylabel' ends at the first
85 character that is not a non-white-space printable character and should
86 be restricted to non-white-space typeable characters. Prior to version
87 3.32, this would transformed to a DOS compatible format of 8.3 with a
88 restricted character set. A *LABEL* clause must contain exactly 1 of
89 the *KERNEL-LIKE DIRECTIVES* and may contain 1 each of the *LABEL-ONLY
90 DIRECTIVES* or *DUAL-PURPOSE DIRECTIVES*.
92 Within a *LABEL*, using multiple *KERNEL-LIKE DIRECTIVES* or reuse of
93 *LABEL-ONLY DIRECTIVES* or *DUAL-PURPOSE DIRECTIVES* will result in an
94 override. Otherwise, multiple instances of the same directive will
95 result in the last being effective.
98 == DUAL-PURPOSE DIRECTIVES ==
99 Use of any of the *DUAL-PURPOSE DIRECTIVES* as *GLOBAL DIRECTIVES* is
100 discouraged if there will be any non-Linux images loaded as *ALL* images
101 will get these, including those manually entered at the 'boot:' prompt.
103 *APPEND* 'options...'::
104 Add one or more options to the kernel command line. These are added
105 both for automatic and manual boots. The options are added at the very
106 beginning of the kernel command line, usually permitting explicitly
107 entered kernel options to override them. This is the equivalent of the
108 LILO "append" option.
110 Use of the parameter 'initrd=' supports multiple filenames separated by
111 commas (ie 'initrd=initrd_file1,initrd_file2') within a single instance.
112 This is mostly useful for initramfs, which can be composed of multiple
113 separate cpio or cpio.gz archives.
115 Note: all initrd files except the last one are zero-padded to a 4K page
116 boundary. This should not affect initramfs.
118 Note: Only the last effective 'initrd=' parameter is used for loading
122 Append nothing. *APPEND* with a single hyphen as argument in a *LABEL*
123 section can be used to override a global *APPEND*.
125 //[FIXME: Shorten subdefinitions]
126 *SYSAPPEND* 'bitmask'::
127 *IPAPPEND* 'bitmask'::
128 (*SYSAPPEND*: 5.10+; *IPAPPEND*: *PXELINUX* only)
129 The *SYSAPPEND* option was introduced in *Syslinux* 5.10; it is an
130 enhancement of a previous option *IPAPPEND* which was only available on
131 *PXELINUX*. 'bitmask' is interpreted as decimal format unless prefixed
132 with "0x" for hexadecimal or "0" (zero) for octal. The 'bitmask' is an
133 OR (sum) of the following integer options:
135 ifndef::doctype-manpage[[horizontal]]
136 *1*::: An option of the following format should be generated, based on
137 the input from the DHCP/BOOTP or PXE boot server and added to the kernel
138 command line(see note below; empty for non-PXELINUX variants):
141 ip=<client-ip>:<boot-server-ip>:<gw-ip>:<netmask>
144 NOTE: The use of option 1 is no substitute for running a DHCP client in
145 the booted system and should instead only be used to seed the client for
146 a request. Without regular renewals, the lease acquired by the PXE BIOS
147 will expire, making the IP address available for reuse by the DHCP
150 *2*::: An option of the following format should be generated, in
151 dash-separated hexadecimal with leading hardware type (same as for the
152 configuration file; see pxelinux.txt.) and added to the kernel command
153 line, allowing an initrd program to determine from which interface the
154 system booted(empty for non-PXELINUX variants):
157 BOOTIF=<hardware-address-of-boot-interface>
160 *4*::: An option of the following format should be generated, in lower
161 case hexadecimal in the format normally used for UUIDs (same as for the
162 configuration file; see pxelinux.txt.) and added to the kernel command
166 SYSUUID=<system uuid>
169 *8*::: (5.10+) indicate the CPU family and certain particularly
170 significant CPU feature bits:
173 CPU=<family><features>
176 The <family> is a single digit from 3 (i386) to 6 (i686 or higher.) The
177 following CPU features are currently reported; additional flags may be
181 P Physical Address Extension (PAE)
182 V Intel Virtualization Technology (VT/VMX)
183 T Intel Trusted Exection Technology (TXT/SMX)
184 X Execution Disable (XD/NX)
186 S AMD SMX virtualization
189 *DMI*::: (5.10+) The following strings are derived from DMI/SMBIOS
190 information if available:
192 Bit String Significance
193 -------------------------------------------------------------
194 0x00010 SYSVENDOR= System vendor name
195 0x00020 SYSPRODUCT= System product name
196 0x00040 SYSVERSION= System version
197 0x00080 SYSSERIAL= System serial number
198 0x00100 SYSSKU= System SKU
199 0x00200 SYSFAMILY= System family
200 0x00400 MBVENDOR= Motherboard vendor name
201 0x00800 MBVERSION= Motherboard version
202 0x01000 MBSERIAL= Motherboard serial number
203 0x02000 MBASSET= Motherboard asset tag
204 0x04000 BIOSVENDOR= BIOS vendor name
205 0x08000 BIOSVERSION= BIOS version
206 0x10000 SYSFF= System form factor
208 If these strings contain white-space characters, they are replaced with
211 The system form factor value is a number defined in the SMBIOS
212 specification, available at http://www.dmtf.org/. As of version 2.7.1
213 of the specification, the following values are defined:
218 4 Low profile desktop
231 17 Main server chassis
234 20 Bus expansion chassis
235 21 Peripheral chassis
239 25 Multi-system chassis
247 == KERNEL-LIKE DIRECTIVES ==
248 // Alpha sort after KERNEL and LINUX
250 Load a kernel-like file 'image' with automatic filetype detection based
251 on file extension, listed under the non-auto-detecting directives,
252 defaulting to *LINUX*.
254 //[FIXME: Should "'image' as " be removed entirely or added to all?
255 *LINUX* is used as an example]
257 Load 'image' as a Linux-like kernel. MEMDISK is an example of a
258 non-Linux kernel loaded in a Linux-like fashion.
261 (*ISOLINUX* only: .bin; *SYSLINUX* only: .bs) Load a boot sector. .bin
262 is a "CD boot sector" and .bs is a regular disk boot sector.
265 (*SYSLINUX* only: .bss) Load a BSS image, a .bs image with the DOS
266 superblock patched in.
269 (.com, .cbt; Removed as of 5.00) Load a *Syslinux* COMBOOT image. .com
270 images may also be runnable from DOS while .cbt images are not. See
274 (.c32) Load a *Syslinux* COM32 (32-bit *COMBOOT*) image. See also
278 Load a new configuration file. The configuration file is read, the
279 working directory is changed (if specified via an *APPEND*), then the
280 configuration file is parsed.
283 (Removed as of 4.05, added 1.65; *ISOLINUX* only: .img) Load a disk
287 (*PXELINUX* 1.53+; *ISOLINUX* ??3.10+; *SYSLINUX* 3.70+)Attempt a
288 different local boot method. The special value -1 causes the boot
289 loader to report failure to the BIOS, which, on recent BIOSes, should
290 mean that the next boot device in the boot sequence should be activated.
291 Values other than those documented may produce undesired results.
293 On *PXELINUX*, 'type' 0 means perform a normal boot. 'type' 4 will
294 perform a local boot with the Universal Network Driver Interface (UNDI)
295 driver still resident in memory. Finally, 'type' 5 will perform a local
296 boot with the entire PXE stack, including the UNDI driver, still
297 resident in memory. All other values are undefined. If you don't know
298 what the UNDI or PXE stacks are, don't worry -- you don't want them,
301 On *ISOLINUX*/*SYSLINUX*, the 'type' specifies the local drive number to
302 boot from; 0x00 is the primary floppy drive and 0x80 is the primary hard
306 (*PXELINUX* only: .0) Load a PXE NBP (Network Boot Program) image. The
307 PXE protocol does not provide any means for specifiying or using a
308 command line or initrd.
311 == LABEL-ONLY DIRECTIVES ==
312 *INITRD* 'initrd_file'::
313 (3.71+) An initrd can be specified in a separate statement (INITRD)
314 instead of as part of the *APPEND* statement; this functionally appends
315 "initrd=initrd_file" to the kernel command line. Like 'initrd=', this
316 also supports multiple comma separated file names (see *APPEND*).
319 == GLOBAL DIRECTIVES - SECONDARY ==
320 These are global directives that are of lesser importance, often
321 affecting the user experience and not the boot process.
323 *ALLOWOPTIONS* 'flag_val'::
324 If 'flag_val' is 0, the user is not allowed to specify any arguments on
325 the kernel command line. The only options recognized are those
326 specified in an *APPEND*) statement. The default is 1.
328 *IMPLICIT* 'flag_val'::
329 If 'flag_val' is 0, do not load a kernel image unless it has been
330 explicitly named in a *LABEL* statement. The default is 1.
332 *TIMEOUT* 'timeout'::
333 Indicates how long to wait at the 'boot:' prompt until booting
334 automatically, in units of 1/10 s. The timeout is cancelled as soon as
335 the user types anything on the keyboard, the assumption being that the
336 user will complete the command line already begun. The timer is reset
337 to 0 upon return from an unsuccessful attempt to boot or from a module.
338 A timeout of zero (the default) will disable the timeout completely.
340 *TOTALTIMEOUT* 'timeout'::
341 Indicates how long to wait until booting automatically, in units of
342 1/10 s. This timeout is *not* cancelled by user input, and can thus be
343 used to deal with serial port glitches or "the user walked away" type
344 situations. A timeout of zero (the default) will disable the timeout
347 Both *TIMEOUT* and *TOTALTIMEOUT* can be used together, for example:
350 # Wait 5 seconds unless the user types something, but
351 # always boot after 15 minutes.
356 // FIXME: be consistent
357 *ONTIMEOUT* 'kernel options...'::
358 Sets the command line invoked on a timeout (which often references a
359 LABEL). If not specified, 'UI' (if used) or 'DEFAULT is used.
361 *ONERROR* 'kernel options...'::
362 If a kernel image is not found (either due to it not existing, or
363 because *IMPLICIT* is set), run the specified command. The faulty
364 command line is appended to the specified options, so if the *ONERROR*
371 and the command line as entered by the user is:
377 *Syslinux* will execute the following as if entered by the user:
380 xyzzy plugh foo bar baz
383 *SERIAL* 'port [baudrate [flowcontrol]]'::
384 Enables a serial port to act as the console. 'port' is a number (0 =
385 /dev/ttyS0 = COM1, etc.) or an I/O port address (e.g. 0x3F8); if
386 'baudrate' is omitted, the baud rate defaults to 9600 bps. The serial
387 parameters are hardcoded to be 8 bits, no parity, 1 stop bit.
389 'flowcontrol' is a combination of the following bits:
394 0x008 - Enable interrupts
395 0x010 - Wait for CTS assertion
396 0x020 - Wait for DSR assertion
397 0x040 - Wait for RI assertion
398 0x080 - Wait for DCD assertion
399 0x100 - Ignore input unless CTS asserted
400 0x200 - Ignore input unless DSR asserted
401 0x400 - Ignore input unless RI asserted
402 0x800 - Ignore input unless DCD asserted
405 All other bits are reserved.
410 0 - No flow control (default)
411 0x303 - Null modem cable detect
412 0x013 - RTS/CTS flow control
413 0x813 - RTS/CTS flow control, modem input
414 0x023 - DTR/DSR flow control
415 0x083 - DTR/DCD flow control
418 For the *SERIAL* directive to be guaranteed to work properly, it should
419 be the first directive in the configuration file.
421 NOTE: 'port' values from 0 to 3 means the first four serial ports
422 detected by the BIOS. They may or may not correspond to the legacy port
423 values 0x3F8, 0x2F8, 0x3E8, 0x2E8.
425 Enabling interrupts (setting the 0x008 bit) may give better
426 responsiveness without setting the *NOHALT* option, but could
427 potentially cause problems with buggy BIOSes.
429 This option is "sticky" and is not automatically reset when loading a
430 new configuration file with the CONFIG command.
432 *NOHALT* 'flag_val'::
433 If 'flag_val' is 1, don't halt the processor while idle. Halting the
434 processor while idle significantly reduces the power consumption, but
435 can cause poor responsiveness to the serial console, especially when
436 using scripts to drive the serial console, as opposed to human
439 *CONSOLE* 'flag_val'::
440 If 'flag_val' is 0, disable output to the normal video console. If
441 'flag_val' is 1, enable output to the video console (this is the
444 Some BIOSes try to forward this to the serial console and sometimes make
445 a total mess thereof, so this option lets you disable the video console
449 Load a font in .psf format before displaying any output (except the
450 copyright line, which is output as ldlinux.sys itself is loaded.)
451 *Syslinux* only loads the font onto the video card; if the .psf file
452 contains a Unicode table it is ignored. This only works on EGA and VGA
453 cards; hopefully it should do nothing on others.
456 Install a simple keyboard map. The keyboard remapper used is *very*
457 simplistic (it simply remaps the keycodes received from the BIOS, which
458 means that only the key combinations relevant in the default layout --
459 usually U.S. English -- can be mapped) but should at least help people
460 with AZERTY keyboard layout and the locations of = and , (two special
461 characters used heavily on the Linux kernel command line.)
463 The included program keytab-lilo.pl from the LILO distribution can be
464 used to create such keymaps. The file keytab-lilo.txt contains the
465 documentation for this program.
467 *DISPLAY* 'filename'::
468 Displays the indicated file on the screen at boot time (before the boot:
469 prompt, if displayed). Please see the section below on *DISPLAY* files.
471 NOTE: If the file is missing, this option is simply ignored.
474 Prints the message on the screen.
476 *PROMPT* 'flag_val'::
477 If 'flag_val' is 0, display the boot: prompt only if the Shift or Alt
478 key is pressed, or Caps Lock or Scroll lock is set (this is the
479 default). If 'flag_val' is 1, always display the boot: prompt.
481 *NOESCAPE* 'flag_val'::
482 If 'flag_val' is set to 1, ignore the Shift/Alt/Caps Lock/Scroll Lock
483 escapes. Use this (together with PROMPT 0) to force the default boot
486 *NOCOMPLETE* 'flag_val'::
487 If 'flag_val' is set to 1, the Tab key does not display labels at the
503 Displays the indicated file on the screen when a function key is pressed
504 at the boot: prompt. This can be used to implement pre-boot online help
505 (presumably for the kernel command line options.) Please see the
506 section below on DISPLAY files.
508 When using the serial console, press <Ctrl-F><digit> to get to the help
509 screens, e.g. <Ctrl-F><2> to get to the F2 screen. For F10-F12, hit
510 <Ctrl-F><A>, <Ctrl-F>B, <Ctrl-F>C. For compatibility with earlier
511 versions, F10 can also be entered as <Ctrl-F>0.
514 (5.00+) Specify a space-separated (' '; 5.00-5.10 was a colon ':') list
515 of directories to search when attempting to load modules. This directive
516 is useful for specifying the directories containing the lib*.c32 library
517 files as other modules may be dependent on these files, but may not
518 reside in the same directory. Multiple instances will append additional
521 *SENDCOOKIES* 'bitmask'::
522 (*PXELINUX* 5.10+) When downloading files over http, the SYSAPPEND
523 strings are prepended with _Syslinux_ and sent to the server as cookies.
524 The cookies are URL-encoded; whitespace is *not* replaced with
527 This command limits the cookies send; 0 means no cookies. The default
528 is -1, meaning send all cookies.
530 This option is "sticky" and is not automatically reset when loading a
531 new configuration file with the CONFIG command.
534 == DISPLAY FILE FORMAT ==
535 DISPLAY and function-key help files are text files in either DOS or UNIX
536 format (with or without <CR>). In addition, the following special codes
539 //[FIXME]: #1 doesn't break; #2 as-is; #3 broken but not on right; #4
541 // horizontal extends the line's label, reducing the definition
542 // tab or space to shift explanation ? align beginning or end?
544 // ifndef::doctype-manpage[[horizontal]]
545 *<FF>*:: {nbsp32} = <Ctrl-L> = ASCII 12 +
546 Clear the screen, home the cursor. Note that the screen is filled with
547 the current display color.
550 = <Ctrl-L> = ASCII 12; Clear the screen, home the cursor. Note that the
551 screen is filled with the current display color.
553 *<FF>*:: <FF> = <Ctrl-L> = ASCII 12
555 Clear the screen, home the cursor. Note that the screen is filled with
556 the current display color.
559 <FF> = <Ctrl-L> = ASCII 12 +
560 Clear the screen, home the cursor. Note that the screen is filled with
561 the current display color.
563 *<SI>*'<bg><fg>':: <SI> = <Ctrl-O> = ASCII 15
565 Set the display colors to the specified background and foreground
566 colors, where <bg> and <fg> are the 2 hex digits representing 1 byte,
567 corresponding to the standard PC display attributes:
569 0 = black 8 = dark grey
570 1 = dark blue 9 = bright blue
571 2 = dark green a = bright green
572 3 = dark cyan b = bright cyan
573 4 = dark red c = bright red
574 5 = dark purple d = bright purple
576 7 = light grey f = white
578 Picking a bright color (8-f) for the background results in the
579 corresponding dark color (0-7), with the foreground flashing.
581 Colors are not visible over the serial console.
583 *<CAN>*'filename<newline>':: <CAN> = <Ctrl-X> = ASCII 24
585 If a VGA display is present, enter graphics mode and display the graphic
586 included in the specified file. The file format is an ad hoc format
587 called LSS16; the included Perl program "ppmtolss16" can be used to
588 produce these images. This Perl program also includes the file format
591 The image is displayed in 640x480 16-color mode. Once in graphics mode,
592 the display attributes (set by <SI> code sequences) work slightly
593 differently: the background color is ignored, and the foreground colors
594 are the 16 colors specified in the image file. For that reason,
595 ppmtolss16 allows you to specify that certain colors should be assigned
596 to specific color indicies.
598 Color indicies 0 and 7, in particular, should be chosen with care: 0 is
599 the background color, and 7 is the color used for the text printed by
602 *<EM>*:: <EM> = <Ctrl-Y> = ASCII 25 +
603 If we are currently in graphics mode, return to text mode.
605 *<DLE>*..*<ETB>*:: <Ctrl-P>..<Ctrl-W> = ASCII 16-23
607 These codes can be used to select which modes to print a certain part of
608 the message file in. Each of these control characters select a specific
609 set of modes (text screen, graphics screen, serial port) for which the
610 output is actually displayed:
612 Character Text Graph Serial
613 ------------------------------------------------------
614 <DLE> = <Ctrl-P> = ASCII 16 No No No
615 <DC1> = <Ctrl-Q> = ASCII 17 Yes No No
616 <DC2> = <Ctrl-R> = ASCII 18 No Yes No
617 <DC3> = <Ctrl-S> = ASCII 19 Yes Yes No
618 <DC4> = <Ctrl-T> = ASCII 20 No No Yes
619 <NAK> = <Ctrl-U> = ASCII 21 Yes No Yes
620 <SYN> = <Ctrl-V> = ASCII 22 No Yes Yes
621 <ETB> = <Ctrl-W> = ASCII 23 Yes Yes Yes
623 For example, the following will actually print out which mode the
626 <DC1>Text mode<DC2>Graphics mode<DC4>Serial port<ETB>
628 *<SUB>*:: <SUB> = <Ctrl-Z> = ASCII 26
630 End of file (DOS convention).
632 *<BEL>*:: <BEL> = <Ctrl-G> = ASCII 7 +
636 == BOOT LOADER IDS USED ==
637 The Linux boot protocol supports a "boot loader ID", a single byte where
638 the upper nybble specifies a boot loader family (3 = *Syslinux*) and the
639 lower nybble is version or, in the case of *Syslinux*, media:
646 In recent versions of Linux, this ID is available as
647 /proc/sys/kernel/bootloader_type.
650 == NOVICE PROTECTION ==
651 *Syslinux* will attempt to detect booting on a machine with too little
652 memory, which means the Linux boot sequence cannot complete. If so, a
653 message is displayed and the boot sequence aborted. Holding down the
654 Ctrl key while booting disables this feature.
656 Any file that *Syslinux* uses can be marked hidden, system or readonly
657 if so is convenient; *Syslinux* ignores all file attributes. The
658 *SYSLINUX* installer automatically sets the readonly/hidden/system
659 attributes on LDLINUX.SYS.
662 Here are some sample config files:
671 APPEND initrd=initrd1.gz,initrd2.gz
676 In this example, serial port use is disabled but can be enabled by
677 uncommenting the first line and utilize serial port 0 at 115200 bps. If
678 'linux' is typed on the command line, the kernel-like file 'vmlinuz' is
679 executed as a Linux kernel, initrd files initrd1.gz and initrd2.gz are
680 loaded as initial ramdisk files (like cpio.gz files for initramfs). If
681 'm' is typed on the command line, the COM32 module 'menu.c32' is
682 executed to launch a menu system.
687 include::com-bug.txt[]
691 include::com-rpt.txt[]
695 This AsciiDoc derived document is a modified version of the original
696 *SYSLINUX* documentation by {author} <{author-email}>. The conversion
697 to an AsciiDoc was made by {editor1} <{editor1-email}>