1 How to netboot using ELILO
2 --------------------------
4 Copyright (C) 2002-2003 Hewlett-Packard Co.
5 Contributed by Stephane Eranian <eranian@hpl.hp.com>
9 EFI has full support for the PXE and DHCP protocol. As such
10 it is relatively easy to boot a machine from the network using EFI.
11 The elilo loader has full support for both PXE and DHCP, therefore
12 it is possible to download the elilo config file, the Linux kernel image
13 and the initial ramdisk from a remote server. There are many ways
14 netbooting can be configured but in this document we focus
15 only on two very common cases:
17 - netboot but use local root filesystem.
18 - booting a diskless machine, i.e., use a NFS root filesystem.
20 1/ How to get EFI to netboot?
22 You do not need any additional software to get EFI to start a netboot session.
23 Any EFI machine can be configured to start a PXE/DHCP session IF it has a network
24 adapter that has support for the UNDI/PXE protocol. Most modern cards do have such
27 To enable netbooting, you need to go into the EFI boot manager maintenance menu
28 and 'Add a boot option'. On the screen you see the list of devices to boot from.
29 At least one of them should be of the form:
31 Load File [Acpi(PNP0A03,0)/Pci(5|0)/Mac(00D0B7A6FC25)]
33 which represent Ethernet card (Mac address). If you don't have such option, it means that
34 you either do not have a network adapter in your machine or it does not have the
35 UNDI/PXE support in its option ROM.
37 You need to select this option and give it a logical name such as 'netboot', for instance.
38 Next, you leave the maintenance menu and go back to the main menu. You now have a new
39 boot menu option. If you select 'netboot' then EFI will start the PXE/DCHP discovery
40 request and look for a server to get an IP address.
42 On the server side, you can use a standard DHCP server, such as the one shipped on
43 Redhat7.2 (dhcpd) or a PXE server (not yet available for Linux, probably available for Windows).
44 In this document we show both options. You also need a TFTP server somewhere on the network,
45 it will be used to download the actual files.
48 2/ Netbooting using DHCP
50 There is nothing specific to EFI that needs to be set in the /etc/dhcpd.conf file.
51 Clearly the filename option must contains the path to the elilo.efi binary.
53 Elilo will auto-detect whether it was downloaded via PXE or DHCP and it will adapt
54 the kind of requests it makes to download the other files that it needs, such as
57 A simple dhcpd.conf file which uses fixed IP addresses could be as follows:
59 subnet 192.168.2.0 netmask 255.255.255.0 {
61 hardware ethernet 00:D0:B7:A6:FC:25;
62 fixed-address 192.168.2.10;
64 option domain-name "mydomain.com";
65 option host-name "test_machine";
66 option routers 192.168.2.1;
67 option subnet-mask 255.255.255.0;
72 For the tftp server, you need to make sure that it is ACTIVATED by inetd or xinetd depending
73 on your distribution. In most distributions, it is disabled by default for security reasons.
74 On distributions using xinetd, you need to check /etc/xinet.d/tftp. For inetd you need to
75 check /etc/inetd.conf. It is typical to have the root directory for tftp be /tftpboot but it
76 can be anything. In this document we will use /tftpboot as the root directory. The files
77 that we need are as follows:
79 - the elilo config file
81 - the initial ramdisk (optional)
84 a/ Location of the files in the tftp directory tree
86 For elilo version 3.3b or higher, it is possible to place the files listed above
87 in any subdirectory below the tftp root. Of course the dhcpd.conf file must
88 point to the location of elilo.efi and provide the path from the tftp root
91 Elilo will look for its config file, the kernel image, the initial ramdisk (optional)
92 only from the directory it was loaded from. This is useful when the same tftp server
93 is used to services many different kind of clients.
95 Here is a simple example, suppose the dhcpd.conf file contains the following definition:
97 subnet 192.168.2.0 netmask 255.255.255.0 {
99 hardware ethernet 00:D0:B7:A6:FC:25;
100 fixed-address 192.168.2.10;
102 filename "/rx6000/elilo.efi";
104 option domain-name "mydomain.com";
105 option host-name "test_machine";
106 option routers 192.168.2.1;
107 option subnet-mask 255.255.255.0;
112 Elilo will be downloaded from /tftpboot/rx6000. Then elilo will look
113 for all the other files it needs in /tftpboot/rx6000. This rule is
114 applied to all files, including the all the variation of the config
117 b/ Getting the config file
119 With DHCP, elilo will first try to download its configuration file. It will try
120 several file names and they are as follows:
123 where AABBCCDD is the hexadecimal representation of the IP address assigned to
124 the machine by DHCP. The hexadecimal string (AABBCCDD) MUST use upper case
127 This filename is an opportunity to specify a machine specific configuration file.
129 2) AA[BB[CC]][-ia32|ia64].conf
130 As of version 3.5, elilo will also look for IPv4 class A,B,C
131 subnet-specific versions of the config file. This is useful when you
132 want to have a common config file for all machines connected to a
135 For example, if your IP address is 10.0.0.1 (0A000001 in hex), elilo
136 will look first for 0A000001.conf, then 0A0000.conf, then 0A00.conf,
139 Elilo will also try architecture-specific versions of subnet-specific
140 config files first (So for example, on an Itanium system,
141 "0A0000-ia64.conf" will be tried before "0A0000.conf")
143 3) elilo-ia32.config or elilo-ia64.conf
145 Depending on the machine (client side) architecture elilo will try the IA-32 or
148 This filename is an opportunity to specify a architecture specific configuration file.
149 This distinction between the architectures is useful when the same TFTP server services
150 the two types of clients : IA32- and IA-64 machines.
154 All files use the same format. Elilo will stop at the first match. In case no file is found,
155 it will try to download a default kernel file name (vmlinux).
157 c/ Getting the kernel
159 The second request from elilo is typically the kernel image. The filename is based on what
160 is in the elilo config file. The path name depends on how the TFTP server is configured.
161 For security reasons it is customary to have the server do a change root in /tftpboot.
162 Hence filenames are relative to /tftpboot and therefore you don't need to specify it.
164 For instance if elilo.conf contains:
169 and the user selects linux-up, then elilo will request a filename of 'vmlinux.249'
170 which must therefore be in /tftpboot. Check the configuration of your TFTP server for
173 d/ Getting the initial ramdisk
175 This step is optional. It follows exactly the same naming rules explained for the kernel image.
176 The initial ramdisk file must therefore be somewhere under /tftpboot.
178 For instance if elilo.conf contains:
182 initrd=ramdisk/initrd.249
184 and the user selects linux-up, then elilo will request a filename of 'ramdisk/initrd.249'
185 which must therefore be under /tftpboot.
188 e/ Getting IP address information
190 When elilo is netbooted, the network filesystem module initializes some elilo variables
191 with the information it received from the DHCP server. At a minimum, it received the
194 The following information is stored in the elilo variables indicated below:
195 - assigned IP address -> %I
196 - assigned netmask -> %M
197 - assigned domainname -> %D
198 - assigned gateway -> %G
200 These variables can be used to dynamically adjust the command line arguments passed to the kernel.
201 See section 5/ below for an example.
203 3/ Netbooting using PXE
205 EFI has builtin support for PXE. In fact it first tries PXE and then default to DHCP
206 when it does not find a valid PXE server.
208 There is a PXE server package available from Linux/ia32 however this package does not
209 have the necessary extensions to talk to the EFI side, at least on IA-64 platforms.
211 There is no need for special options or compile time flags to get elilo to work
212 with PXE instead of standard DHCP. When netbooted, elilo will automatically detect
213 if it has been downloaded via PXE or DHCP and it will adujst how subsequent files
216 You need a special version of the DHCPD server developed by the Internet Software Consortium
217 (http://www.isc.org) with a special patch to add the PXE extensions. Unfortunately as of
218 version 3.0xx, the patch has not yet made it into the official tree. It is supposed to show
219 up in version 3.1 of the dhcpd server.
221 In any case, the elilo package contains a simple example of how you can configure the
222 /etc/dhcpd.conf file for a PXE-aware DHCP server using the extensions provided in the
223 patch. You can look in examples/dhcpd-pxe.conf. The syntax is very different from
224 a standard dhcpd server.
226 The key elements to keep in mind are the PXE layers used by elilo to request the different
229 Layer 0 : to get the name of the boot loader (elilo.efi)
230 Layer 1 : to get the name of the elilo config file
231 Layer 2 : to get the name of the kernel image
233 There is an IMPORTANT distinction between those layers. The first two (0,1) and requested
234 systematically whereas the last one is used only when the configuration file is not found, i.e.,
235 what is the default kernel to boot. The actual files are STILL downloaded via TFTP. Therefore
236 the TFTP server must also be configured (see previous section for more on this).
239 a/ Getting the config file
241 In this mode, elilo use the PXE layer 1 to get the config file to use. Therefore this must
242 be set on the server side. Elilo will use the following sequence when
243 looking for a config file:
245 - use the name provide by the PXE server Layer 1 or
247 - elilo-ia64.conf/elilo-ia32.conf or
251 Elilo stops at the first match. With PXE, elilo does not try to download a config file named after
252 the assigned IP address as it does for DHCP because there is enough flexibility in the PXE server
253 configuration to do this.
255 b/ Getting the kernel image
257 When there is no config file, elilo will use the kernel name returned by
258 PXE layer 2. If it is not specified there, then it default to 'vmlinux'.
260 c/ Getting the initial ramdisk
262 The filename for the ramdisk MUST come from the config file. Elilo does not use a PXE layer
263 to ask for a default name.
265 d/ Getting IP address information
267 When elilo is netbooted, the network filesystem module initializes some elilo variables
268 with the information it received from the DHCP server. At a minimum, it received the
271 The following information is stored in the variables indicated below:
272 - assigned IP address -> %I
273 - assigned netmask -> %M
274 - assigned domainname -> %D
275 - assigned gateway -> %G
277 These variables can be used to dynamically adjust the command line arguments passed to the kernel.
278 See section 5/ below for an example of how to use the variable.
281 4/ Netbooting and using a local root filesystem
283 This is the simplest configuration where the boot loader, its config file, the kernel
284 and its optional initial ramdisk are downloaded from the network BUT the kernel uses
285 the local disk for its root filesystem.
287 For such configuration there is no special option necessary in the elilo config file.
288 You simply need to specify which partition is the root partition. A typical elilo.conf
289 would look as follows:
294 initrd=ramdisk/initrd.249
296 5/ Netbooting a diskless machine
298 In this configuration we do not use the local machine's disks but instead rely on
299 a remote server to provide the root filesystem via NFS.
303 By default most kernels shipped by distributors do not have the support
304 compiled in for such configuration. This means that you need to recompile
305 your own kernel. For instance, vmlinuz-2.4.9 as shipped in Redhat7.2 on
306 both ia32 and ia64 platforms does not have the support builtin.
308 To get this configuration to work, you need to have a kernel compiled
309 such that it accepts a root filesystem over NFS (CONFIG_ROOT_NFS). This
310 necessitates that the network stack be configured with the, so called,
311 IP plug-and-play support (CONFIG_IP_PNP).
313 b/ On the server side
316 - a NFS file server to provide the root filesystem.
317 - a DHCP/PXE server to get the IP address and download the boot loader.
319 Note that both do not need to be on the same machine. There is no special
320 DHCP/PXE configuration option required to get this working. All you need
321 is a kernel compiled with the options mentioned in a/. You also need to
322 make sure that the permission on the NFS server are set appropriately
323 to allow root access from the client machine (no_root_squash), see
324 man 'exports' for more on this.
326 c/ The elilo configuration file
328 To boot successfully, the kernel needs to:
329 - get an IP address and related networking parameters
330 - contact the NFS server to get its root filesystem
332 The 2.4.x kernel series provides several options to get the IP address:
333 - it can do an internal DHCP request (CONFIG_IP_PNP_DHCP)
334 - it can do an internal RARP request (CONFIG_IP_PNP_RARP)
335 - it can do an internal BOOTP request (CONFIG_IP_PNP_BOOTP)
336 - it can get the IP address from the command line
338 The choice is up to you but it is a little bit stupid to go through a
339 DHCP/BOOTP/RARP phase again when this is already done by the EFI firmware.
340 So in this document, we describe how you can pass the information provided
341 by EFI on the command line of the kernel.
343 The syntax used to pass IP information on the command line is described in
344 the kernel source tree in Documentation/nfsroot.txt. The option is called
345 "ip=" and has the following syntax:
347 ip=<client-ip>:<server-ip>:<gw-ip>:<netmask>:<hostname>:<device>:<autoconf>
349 To designate the NFS server, you must use the "nfsroot=" option. It has the
351 nfsroot=[<server-ip>:]<root-dir>[,<nfs-options>]
353 Depending on how you want your system configured you can hardcode the
354 values of the parameters in the elilo configuration file. For instance:
358 description="kernel with NFS root"
359 append="root=/dev/nfs nfsroot=192.168.2.22:/ia64_rootfs ip=192.168.2.5::192.168.2.1:255.255.255.0:test_machine:eth0:on"
361 Note the root=/dev/nfs indicates that the root filesystem is over NFS.
363 This example works fine however, it is not very flexible because the IP
364 address, the gateway, netmask and hostname are fixed and do not used the
365 values EFI used to download the boot loader and the kernel.
367 Elilo provides a way to dynamically customize the parameters passed on the
368 command line using substitution variables. We describe those variables in
369 elilovar.txt. The basic idea is to allow the parameters to use the dynamic
370 information obtained by the DHCP/PXE phase.
372 The network support in elilo defines several variables which contained
373 network related information produced by the DHCP/PXE phase. The set of
375 %I -> the IP address obtained by DHCP/PXE
376 %M -> the netmask obtained by DHCP/PXE
377 %G -> the gateway obtained by DHCP/PXE
378 %H -> the hostname obtained by DHCP/PXE
379 %D -> the domain name obtained by DHCP/PXE
381 So, the configuration file can then be customized as follows:
384 description="kernel with NFS root"
385 append="root=/dev/nfs nfsroot=192.168.2.22:/ia64_rootfs ip=%I::%G:%M:%H:eth0:on"
387 Not all parameters are necessary or even used by the kernel or the user level
388 configuration scripts. There is no variable to substitute the NFS server or
389 the mount point on that server.
392 In the case of a DHCP boot, this type of customization makes sense only for
393 the shared configuration file, elilo-ia64.conf/elilo-ia32.conf or elilo.conf.
394 The configuration file based on the IP address (such as C0A80205.conf in this
395 case) would provide another way of customizing parameters for a specific
396 client (IP address). The same thing holds if the name of the config file
397 returned by the PXE server is specific to a client.
402 More information on the PXE protocol can be found at the following web site:
404 http://developer.intel.com/ial/wfm/
406 The source code for the standard and (possibly) PXE-enhanced DHCPD can be