pxelinux.doc - pub/scm/boot/syslinux/syslinux - Git at Google

                                PXELINUX

     A bootloader for Linux using the PXE network booting protocol

 		Copyright (C) 1994-2001 H. Peter Anvin

 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.

 ----------------------------------------------------------------------

 PXELINUX is a SYSLINUX derivative, for booting Linux off a network
 server, using a network ROM conforming to the Intel PXE (Pre-Execution
 Environment) specification.  PXELINUX is *not* a program that is
 intended to be flashed or burned into a PROM on the network card; if
 you want that, check out NILO (http://www.nilo.org/).  NILO can also
 be used to create a PXE-compliant boot PROM for most network cards
 which have drivers for Linux or FreeBSD.


     ++++ HOW TO CONFIGURE PXELINUX ++++

 PXELINUX operates in many ways like SYSLINUX.  If you are not familiar
 with SYSLINUX, read syslinux.doc first, since this documentation only
 explains the differences.

 On the TFTP server, create the directory "/tftpboot", and copy the
 following files to it:

 	pxelinux.0		- from the SYSLINUX distribution

 	any kernel or initrd images you want to boot

 Finally, create the directory "/tftpboot/pxelinux.cfg".  The
 configuration file (equivalent of syslinux.cfg -- see syslinux.doc for
 the options here) will live in this directory.  Because more than one
 system may be booted from the same server, the configuration file name
 depends on the IP address of the booting machine.  PXELINUX will
 search for its config file on the boot server in the following way:

   First, it will search for the config file using its own IP address
   in upper case hexadecimal, e.g. 192.0.2.91 -> C000025B
   (you can use the included progam "gethostip" to compute the
   hexadecimal IP address for any host.)

   If that file is not found, it will remove one hex digit and try
   again.  Ultimately, it will try looking for a file named "default"
   (in lower case).

   As an example, for 192.0.2.91, it will try C000025B, C000025,
   C00002, C0000, C000, C00, C0, C, and default, in that order.

 (See also the section on special DHCP options.)

 It should be noted that all filename references are relative to the
 directory pxelinux.0 lives in (usually /tftpboot).  PXELINUX
 generally requires that filenames (including any relative path) are 63
 characters or shorter in length.

 PXELINUX does not support MTFTP, and I have no immediate plans of
 doing so.  It is of course possible to use MTFTP for the initial boot,
 if you have such a setup.  MTFTP server setup is beyond the scope of
 this document.


     ++++ SETTING UP THE TFTP SERVER ++++

 PXELINUX currently requires that the boot server has a TFTP server
 which supports the "tsize" TFTP option (RFC 1784/RFC 2349).  The
 "tftp-hpa" TFTP server, which support options, is available at:

 	http://www.kernel.org/pub/software/network/tftp/
 	ftp://www.kernel.org/pub/software/network/tftp/

 ... and on any kernel.org mirror (see http://www.kernel.org/mirrors/).

 Another TFTP server which supports this is atftp by Jean-Pierre
 Lefebvre:

 	ftp://ftp.mamalinux.com/pub/atftp/

 If your boot server is running Windows (and you can't fix that), try
 tftpd32 by Philippe Jounin (you need version 2.11 or later; previous
 versions had a bug which made it incompatible with PXELINUX):

 	http://tftpd32.jounin.net/


     ++++ SETTING UP THE DHCP SERVER ++++

 The PXE protocol uses a very complex set of extensions to DHCP or
 BOOTP.  However, most PXE implementations -- this includes all Intel
 ones version 0.99n and later -- seem to be able to boot in a
 "conventional" DHCP/TFTP configuration.  Assuming you don't have to
 support any very old or otherwise severely broken clients, this is
 probably the best configuration unless you already have a PXE boot
 server on your network.

 A sample DHCP setup, using the "conventional TFTP" configuration,
 would look something like the following, using ISC dhcp 2.0 dhcpd.conf
 syntax:

         allow booting;
         allow bootp;

 	# Standard configuration directives...

         option domain-name "<domain name>";
         option subnet-mask <subnet mask>;
         option broadcast-address <broadcast address>;
         option domain-name-servers <dns servers>;
         option routers <default router>;

 	# Group the PXE bootable hosts together
 	group {
 		# PXE-specific configuration directives...
 		next-server <TFTP server address>;
 		filename "/tftpboot/pxelinux.0";

 		# You need an entry like this for every host
 		# unless you're using dynamic addresses
 	        host <hostname> {
         	        hardware ethernet <ethernet address>;
                		fixed-address <hostname>;
         	}
 	}

 Note that if your particular TFTP daemon runs under chroot (tftp-hpa
 will do this if you specify the -s (secure) option; this is highly
 recommended), you almost certainly should not include the /tftpboot
 prefix in the filename statement.

 If this does not work for your configuration, you probably should set
 up a "PXE boot server" on port 4011 of your TFTP server; a free PXE
 boot server is available at:

 	http://www.kano.org.uk/projects/pxe/

 With such a boot server defined, your DHCP configuration should look
 the same except for an "option dhcp-class-identifier" ("option
 vendor-class-identifier" if you are using DHCP 3.0):

         allow booting;
         allow bootp;

 	# Standard configuration directives...

         option domain-name "<domain name>";
         option subnet-mask <subnet mask>;
         option broadcast-address <broadcast address>;
         option domain-name-servers <dns servers>;
         option routers <default router>;

 	# Group the PXE bootable hosts together
 	group {
 		# PXE-specific configuration directives...
 	        option dhcp-class-identifier "PXEClient";
 		next-server <pxe boot server address>;

 		# You need an entry like this for every host
 		# unless you're using dynamic addresses
 	        host <hostname> {
         	        hardware ethernet <ethernet address>;
                		fixed-address <hostname>;
         	}
 	}

 Here, the boot file name is obtained from the PXE server.

 If the "conventional TFTP" configuration doesn't work on your clients,
 and setting up a PXE boot server is not an option, you can attempt the
 following configuration.  It has been known to boot some
 configurations correctly; however, there are no guarantees:

         allow booting;
         allow bootp;

 	# Standard configuration directives...

         option domain-name "<domain name>";
         option subnet-mask <subnet mask>;
         option broadcast-address <broadcast address>;
         option domain-name-servers <dns servers>;
         option routers <default router>;

 	# Group the PXE bootable hosts together
 	group {
 		# PXE-specific configuration directives...
 	        option dhcp-class-identifier "PXEClient";
 		option vendor-encapsulated-options 09:0f:80:00:0c:4e:65:74:77:6f:72:6b:20:62:6f:6f:74:0a:07:00:50:72:6f:6d:70:74:06:01:02:08:03:80:00:00:47:04:80:00:00:00:ff;
 		next-server <TFTP server>;
 		filename "/tftpboot/pxelinux.0";

 		# You need an entry like this for every host
 		# unless you're using dynamic addresses
 	        host <hostname> {
         	        hardware ethernet <ethernet address>;
                		fixed-address <hostname>;
         	}
 	}

 Note that this *will not* boot some clients that *will* boot with the
 "conventional TFTP" configuration; Intel Boot Client 3.0 and later are
 known to fall into this category.


     ++++ SPECIAL DHCP OPTIONS ++++

 PXELINUX (starting with version 1.62) supports the following
 nonstandard DHCP options, which depending on your DHCP server you may
 be able to use to customize the specific behaviour of PXELINUX:

 Option 208	pxelinux.magic
 	- Must be set to F1:00:74:7E (241.0.116.126) for PXELINUX to
 	  recognize any special DHCP options whatsoever.

 Option 209	pxelinux.configfile
 	- Specifies the PXELINUX configuration file name.

 Option 210	pxelinux.pathprefix
 	- Specifies the PXELINUX common path prefix, instead of
 	  deriving it from the boot file name.  This almost certainly
 	  needs to end in whatever character the TFTP server OS uses
 	  as a pathname separator, e.g. slash (/) for Unix.

 Option 211	pxelinux.reboottime
 	- Specifies, in seconds, the time to wait before reboot in the
 	  event of TFTP failure.  0 means wait "forever" (in reality,
 	  it waits approximately 136 years.)

 ISC dhcp 3.0 supports a rather nice syntax for specifying custom
 options; you can use the following syntax in dhcpd.conf if you are
 running this version of dhcpd:

 	option space pxelinux;
 	option pxelinux.magic      code 208 = string;
 	option pxelinux.configfile code 209 = text;
 	option pxelinux.pathprefix code 210 = text;
 	option pxelinux.reboottime code 211 = unsigned integer 32;

 Then, inside your PXELINUX-booting group or class (whereever you have
 the PXELINUX-related options, such as the filename option), you can
 add, for example:

 	# Always include the following lines for all PXELINUX clients
 	site-option-space "pxelinux";
 	option pxelinux.magic f1:00:74:7e;
 	if exists dhcp-parameter-request-list {
 		# Always send the PXELINUX options
 		append dhcp-parameter-request-list 208, 209, 210, 211;
 	}
 	# These lines should be customized to your setup
 	option pxelinux.configfile "configs/common";
 	option pxelinux.pathprefix "/tftpboot/pxelinux/files/";
 	option pxelinux.reboottime 30;
 	filename "/tftpboot/pxelinux/pxelinux.bin";

 Note that the configfile is relative to the pathprefix: this will look
 for a config file called /tftpboot/pxelinux/files/configs/common on
 the TFTP server.

 The "append dhcp-parameter-request-list" is an undocumented (as of
 DHCP 3.0rc2pl1) option which forces the DHCP server to send the
 PXELINUX-specific options, even though they are not explicitly
 requested.

 Using ISC dhcp 3.0 you can create a lot of these strings on the fly.
 For example, to use the hexadecimal form of the hardware address as
 the configuration file name, you could do something like:

 	site-option-space "pxelinux";
 	option pxelinux.magic f1:00:74:7e;
 	if exists dhcp-parameter-request-list {
 		# Always send the PXELINUX options
 		append dhcp-parameter-request-list 208, 209, 210, 211;
 	}
 	option pxelinux.configfile =
 		concat("pxelinux.cfg/", binary-to-ascii(16, 8, ":", hardware));
 	filename "/tftpboot/pxelinux.bin";

 If you used this from a client whose Ethernet address was
 58:FA:84:CF:55:0E, this would look for a configuration file named
 "/tftpboot/pxelinux.cfg/1:58:fa:84:cf:55:e".


     ++++ SOME NOTES ++++

 If the boot fails, PXELINUX (unlike SYSLINUX) will not wait forever;
 rather, if it has not received any input for approximately five
 minutes after displaying an error message, it will reset the machine.
 This allows an unattended machine to recover in case it had bad enough
 luck of trying to boot at the same time the TFTP server goes down.

 Lots of PXE stacks, especially old ones, have various problems of
 varying degrees of severity.  Please see:

 	http://syslinux.zytor.com/hardware.php

 ... for a list of currently known hardware problems, with workarounds
 if known.


     ++++ KEEPING THE PXE STACK AROUND ++++

 Normally, PXELINUX will unload the PXE and UNDI stacks before invoking
 the kernel.  In special circumstances (for example, when using MEMDISK
 to boot an operating system with an UNDI network driver) it might be
 desirable to keep the PXE stack in memory.  If the option "keeppxe"
 is given on the kernel command line, PXELINUX will keep the PXE and
 UNDI stacks in memory.  (If you don't know what this means, you
 probably don't need it.)


     ++++ CURRENTLY KNOWN PROBLEMS ++++

 The following problems are known with PXELINUX, so far:

 + Requires a TFTP server which supports the "tsize" option.
 + The error recovery routine doesn't work quite right.  For right now,
   it just does a hard reset - seems good enough.
 + We should probably call the UDP receive function in the keyboard
   entry loop, so that we answer ARP requests.
 + Boot sectors/disk images are not supported yet.

 If you have additional problems, please contact the SYSLINUX mailing
 list (see syslinux.doc for the address.)
	PXELINUX

	A bootloader for Linux using the PXE network booting protocol

	Copyright (C) 1994-2001 H. Peter Anvin

	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.

	----------------------------------------------------------------------

	PXELINUX is a SYSLINUX derivative, for booting Linux off a network
	server, using a network ROM conforming to the Intel PXE (Pre-Execution
	Environment) specification. PXELINUX is not a program that is
	intended to be flashed or burned into a PROM on the network card; if
	you want that, check out NILO (http://www.nilo.org/). NILO can also
	be used to create a PXE-compliant boot PROM for most network cards
	which have drivers for Linux or FreeBSD.


	++++ HOW TO CONFIGURE PXELINUX ++++

	PXELINUX operates in many ways like SYSLINUX. If you are not familiar
	with SYSLINUX, read syslinux.doc first, since this documentation only
	explains the differences.

	On the TFTP server, create the directory "/tftpboot", and copy the
	following files to it:

	pxelinux.0 - from the SYSLINUX distribution

	any kernel or initrd images you want to boot

	Finally, create the directory "/tftpboot/pxelinux.cfg". The
	configuration file (equivalent of syslinux.cfg -- see syslinux.doc for
	the options here) will live in this directory. Because more than one
	system may be booted from the same server, the configuration file name
	depends on the IP address of the booting machine. PXELINUX will
	search for its config file on the boot server in the following way:

	First, it will search for the config file using its own IP address
	in upper case hexadecimal, e.g. 192.0.2.91 -> C000025B
	(you can use the included progam "gethostip" to compute the
	hexadecimal IP address for any host.)

	If that file is not found, it will remove one hex digit and try
	again. Ultimately, it will try looking for a file named "default"
	(in lower case).

	As an example, for 192.0.2.91, it will try C000025B, C000025,
	C00002, C0000, C000, C00, C0, C, and default, in that order.

	(See also the section on special DHCP options.)

	It should be noted that all filename references are relative to the
	directory pxelinux.0 lives in (usually /tftpboot). PXELINUX
	generally requires that filenames (including any relative path) are 63
	characters or shorter in length.

	PXELINUX does not support MTFTP, and I have no immediate plans of
	doing so. It is of course possible to use MTFTP for the initial boot,
	if you have such a setup. MTFTP server setup is beyond the scope of
	this document.


	++++ SETTING UP THE TFTP SERVER ++++

	PXELINUX currently requires that the boot server has a TFTP server
	which supports the "tsize" TFTP option (RFC 1784/RFC 2349). The
	"tftp-hpa" TFTP server, which support options, is available at:

	http://www.kernel.org/pub/software/network/tftp/
	ftp://www.kernel.org/pub/software/network/tftp/

	... and on any kernel.org mirror (see http://www.kernel.org/mirrors/).

	Another TFTP server which supports this is atftp by Jean-Pierre
	Lefebvre:

	ftp://ftp.mamalinux.com/pub/atftp/

	If your boot server is running Windows (and you can't fix that), try
	tftpd32 by Philippe Jounin (you need version 2.11 or later; previous
	versions had a bug which made it incompatible with PXELINUX):

	http://tftpd32.jounin.net/


	++++ SETTING UP THE DHCP SERVER ++++

	The PXE protocol uses a very complex set of extensions to DHCP or
	BOOTP. However, most PXE implementations -- this includes all Intel
	ones version 0.99n and later -- seem to be able to boot in a
	"conventional" DHCP/TFTP configuration. Assuming you don't have to
	support any very old or otherwise severely broken clients, this is
	probably the best configuration unless you already have a PXE boot
	server on your network.

	A sample DHCP setup, using the "conventional TFTP" configuration,
	would look something like the following, using ISC dhcp 2.0 dhcpd.conf
	syntax:

	allow booting;
	allow bootp;

	# Standard configuration directives...

	option domain-name "<domain name>";
	option subnet-mask <subnet mask>;
	option broadcast-address <broadcast address>;
	option domain-name-servers <dns servers>;
	option routers <default router>;

	# Group the PXE bootable hosts together
	group {
	# PXE-specific configuration directives...
	next-server <TFTP server address>;
	filename "/tftpboot/pxelinux.0";

	# You need an entry like this for every host
	# unless you're using dynamic addresses
	host <hostname> {
	hardware ethernet <ethernet address>;
	fixed-address <hostname>;
	}
	}

	Note that if your particular TFTP daemon runs under chroot (tftp-hpa
	will do this if you specify the -s (secure) option; this is highly
	recommended), you almost certainly should not include the /tftpboot
	prefix in the filename statement.

	If this does not work for your configuration, you probably should set
	up a "PXE boot server" on port 4011 of your TFTP server; a free PXE
	boot server is available at:

	http://www.kano.org.uk/projects/pxe/

	With such a boot server defined, your DHCP configuration should look
	the same except for an "option dhcp-class-identifier" ("option
	vendor-class-identifier" if you are using DHCP 3.0):

	allow booting;
	allow bootp;

	# Standard configuration directives...

	option domain-name "<domain name>";
	option subnet-mask <subnet mask>;
	option broadcast-address <broadcast address>;
	option domain-name-servers <dns servers>;
	option routers <default router>;

	# Group the PXE bootable hosts together
	group {
	# PXE-specific configuration directives...
	option dhcp-class-identifier "PXEClient";
	next-server <pxe boot server address>;

	# You need an entry like this for every host
	# unless you're using dynamic addresses
	host <hostname> {
	hardware ethernet <ethernet address>;
	fixed-address <hostname>;
	}
	}

	Here, the boot file name is obtained from the PXE server.

	If the "conventional TFTP" configuration doesn't work on your clients,
	and setting up a PXE boot server is not an option, you can attempt the
	following configuration. It has been known to boot some
	configurations correctly; however, there are no guarantees:

	allow booting;
	allow bootp;

	# Standard configuration directives...

	option domain-name "<domain name>";
	option subnet-mask <subnet mask>;
	option broadcast-address <broadcast address>;
	option domain-name-servers <dns servers>;
	option routers <default router>;

	# Group the PXE bootable hosts together
	group {
	# PXE-specific configuration directives...
	option dhcp-class-identifier "PXEClient";
	option vendor-encapsulated-options 09:0f:80:00:0c:4e:65:74:77:6f:72:6b:20:62:6f:6f:74:0a:07:00:50:72:6f:6d:70:74:06:01:02:08:03:80:00:00:47:04:80:00:00:00:ff;
	next-server <TFTP server>;
	filename "/tftpboot/pxelinux.0";

	# You need an entry like this for every host
	# unless you're using dynamic addresses
	host <hostname> {
	hardware ethernet <ethernet address>;
	fixed-address <hostname>;
	}
	}

	Note that this will not boot some clients that will boot with the
	"conventional TFTP" configuration; Intel Boot Client 3.0 and later are
	known to fall into this category.


	++++ SPECIAL DHCP OPTIONS ++++

	PXELINUX (starting with version 1.62) supports the following
	nonstandard DHCP options, which depending on your DHCP server you may
	be able to use to customize the specific behaviour of PXELINUX:

	Option 208 pxelinux.magic
	- Must be set to F1:00:74:7E (241.0.116.126) for PXELINUX to
	recognize any special DHCP options whatsoever.

	Option 209 pxelinux.configfile
	- Specifies the PXELINUX configuration file name.

	Option 210 pxelinux.pathprefix
	- Specifies the PXELINUX common path prefix, instead of
	deriving it from the boot file name. This almost certainly
	needs to end in whatever character the TFTP server OS uses
	as a pathname separator, e.g. slash (/) for Unix.

	Option 211 pxelinux.reboottime
	- Specifies, in seconds, the time to wait before reboot in the
	event of TFTP failure. 0 means wait "forever" (in reality,
	it waits approximately 136 years.)

	ISC dhcp 3.0 supports a rather nice syntax for specifying custom
	options; you can use the following syntax in dhcpd.conf if you are
	running this version of dhcpd:

	option space pxelinux;
	option pxelinux.magic code 208 = string;
	option pxelinux.configfile code 209 = text;
	option pxelinux.pathprefix code 210 = text;
	option pxelinux.reboottime code 211 = unsigned integer 32;

	Then, inside your PXELINUX-booting group or class (whereever you have
	the PXELINUX-related options, such as the filename option), you can
	add, for example:

	# Always include the following lines for all PXELINUX clients
	site-option-space "pxelinux";
	option pxelinux.magic f1:00:74:7e;
	if exists dhcp-parameter-request-list {
	# Always send the PXELINUX options
	append dhcp-parameter-request-list 208, 209, 210, 211;
	}
	# These lines should be customized to your setup
	option pxelinux.configfile "configs/common";
	option pxelinux.pathprefix "/tftpboot/pxelinux/files/";
	option pxelinux.reboottime 30;
	filename "/tftpboot/pxelinux/pxelinux.bin";

	Note that the configfile is relative to the pathprefix: this will look
	for a config file called /tftpboot/pxelinux/files/configs/common on
	the TFTP server.

	The "append dhcp-parameter-request-list" is an undocumented (as of
	DHCP 3.0rc2pl1) option which forces the DHCP server to send the
	PXELINUX-specific options, even though they are not explicitly
	requested.

	Using ISC dhcp 3.0 you can create a lot of these strings on the fly.
	For example, to use the hexadecimal form of the hardware address as
	the configuration file name, you could do something like:

	site-option-space "pxelinux";
	option pxelinux.magic f1:00:74:7e;
	if exists dhcp-parameter-request-list {
	# Always send the PXELINUX options
	append dhcp-parameter-request-list 208, 209, 210, 211;
	}
	option pxelinux.configfile =
	concat("pxelinux.cfg/", binary-to-ascii(16, 8, ":", hardware));
	filename "/tftpboot/pxelinux.bin";

	If you used this from a client whose Ethernet address was
	58:FA:84:CF:55:0E, this would look for a configuration file named
	"/tftpboot/pxelinux.cfg/1:58:fa:84:cf:55:e".


	++++ SOME NOTES ++++

	If the boot fails, PXELINUX (unlike SYSLINUX) will not wait forever;
	rather, if it has not received any input for approximately five
	minutes after displaying an error message, it will reset the machine.
	This allows an unattended machine to recover in case it had bad enough
	luck of trying to boot at the same time the TFTP server goes down.

	Lots of PXE stacks, especially old ones, have various problems of
	varying degrees of severity. Please see:

	http://syslinux.zytor.com/hardware.php

	... for a list of currently known hardware problems, with workarounds
	if known.


	++++ KEEPING THE PXE STACK AROUND ++++

	Normally, PXELINUX will unload the PXE and UNDI stacks before invoking
	the kernel. In special circumstances (for example, when using MEMDISK
	to boot an operating system with an UNDI network driver) it might be
	desirable to keep the PXE stack in memory. If the option "keeppxe"
	is given on the kernel command line, PXELINUX will keep the PXE and
	UNDI stacks in memory. (If you don't know what this means, you
	probably don't need it.)


	++++ CURRENTLY KNOWN PROBLEMS ++++

	The following problems are known with PXELINUX, so far:

	+ Requires a TFTP server which supports the "tsize" option.
	+ The error recovery routine doesn't work quite right. For right now,
	it just does a hard reset - seems good enough.
	+ We should probably call the UDP receive function in the keyboard
	entry loop, so that we answer ARP requests.
	+ Boot sectors/disk images are not supported yet.

	If you have additional problems, please contact the SYSLINUX mailing
	list (see syslinux.doc for the address.)