1 SPDX-License-Identifier: GPL-2.0+
3 * Copyright 2010-2011 Calxeda, Inc.
6 The 'pxe' commands provide a near subset of the functionality provided by
7 the PXELINUX boot loader. This allows U-Boot based systems to be controlled
8 remotely using the same PXE based techniques that many non U-Boot based servers
18 follows PXELINUX's rules for retrieving configuration files from a tftp
19 server, and supports a subset of PXELINUX's config file syntax.
23 'pxe get' requires two environment variables to be set:
25 pxefile_addr_r - should be set to a location in RAM large enough to hold
26 pxe files while they're being processed. Up to 16 config files may be
27 held in memory at once. The exact number and size of the files varies with
28 how the system is being used. A typical config file is a few hundred bytes
31 bootfile,serverip - these two are typically set in the DHCP response
32 handler, and correspond to fields in the DHCP response.
34 'pxe get' optionally supports these two environment variables being set:
36 ethaddr - this is the standard MAC address for the ethernet adapter in use.
37 'pxe get' uses it to look for a configuration file specific to a system's
40 pxeuuid - this is a UUID in standard form using lower case hexadecimal
41 digits, for example, 550e8400-e29b-41d4-a716-446655440000. 'pxe get' uses
42 it to look for a configuration file based on the system's UUID.
46 'pxe get' repeatedly tries to download config files until it either
47 successfully downloads one or runs out of paths to try. The order and
48 contents of paths it tries mirrors exactly that of PXELINUX - you can
49 read in more detail about it at:
51 http://syslinux.zytor.com/wiki/index.php/Doc/pxelinux
55 syntax: pxe boot [pxefile_addr_r]
57 Interprets a pxe file stored in memory.
59 pxefile_addr_r is an optional argument giving the location of the pxe file.
60 The file must be terminated with a NUL byte.
64 There are some environment variables that may need to be set, depending
67 pxefile_addr_r - if the optional argument pxefile_addr_r is not supplied,
68 an environment variable named pxefile_addr_r must be supplied. This is
69 typically the same value as is used for the 'pxe get' command.
71 bootfile - typically set in the DHCP response handler based on the
72 same field in the DHCP respone, this path is used to generate the base
73 directory that all other paths to files retrieved by 'pxe boot' will use.
74 If no bootfile is specified, paths used in pxe files will be used as is.
76 serverip - typically set in the DHCP response handler, this is the IP
77 address of the tftp server from which other files will be retrieved.
79 kernel_addr_r, initrd_addr_r - locations in RAM at which 'pxe boot' will
80 store the kernel(or FIT image) and initrd it retrieves from tftp. These
81 locations will be passed to the bootm command to boot the kernel. These
82 environment variables are required to be set.
84 fdt_addr_r - location in RAM at which 'pxe boot' will store the fdt blob it
85 retrieves from tftp. The retrieval is possible if 'fdt' label is defined in
86 pxe file and 'fdt_addr_r' is set. If retrieval is possible, 'fdt_addr_r'
87 will be passed to bootm command to boot the kernel.
89 fdt_addr - the location of a fdt blob. 'fdt_addr' will be passed to bootm
90 command if it is set and 'fdt_addr_r' is not passed to bootm command.
92 fdtoverlay_addr_r - location in RAM at which 'pxe boot' will temporarily store
93 fdt overlay(s) before applying them to the fdt blob stored at 'fdt_addr_r'.
95 pxe_label_override - override label to be used, if exists, instead of the
96 default label. This will allow consumers to choose a pxe label at
97 runtime instead of having to prompt the user. If "pxe_label_override" is set
98 but does not exist in the pxe menu, pxe would fallback to the default label if
99 given, and no failure is returned but rather a warning message.
103 The pxe file format is nearly a subset of the PXELINUX file format; see
104 http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed of one line
105 commands - global commands, and commands specific to labels. Lines begining
106 with # are treated as comments. White space between and at the beginning of
109 The size of pxe files and the number of labels is only limited by the amount
110 of RAM available to U-Boot. Memory for labels is dynamically allocated as
111 they're parsed, and memory for pxe files is statically allocated, and its
112 location is given by the pxefile_addr_r environment variable. The pxe code is
113 not aware of the size of the pxefile memory and will outgrow it if pxe files
116 Supported global commands
117 -------------------------
118 Unrecognized commands are ignored.
120 default <label> - the label named here is treated as the default and is
121 the first label 'pxe boot' attempts to boot.
123 menu title <string> - sets a title for the menu of labels being displayed.
125 menu include <path> - use tftp to retrieve the pxe file at <path>, which
126 is then immediately parsed as if the start of its
127 contents were the next line in the current file. nesting
128 of include up to 16 files deep is supported.
130 prompt <flag> - if 1, always prompt the user to enter a label to boot
131 from. if 0, only prompt the user if timeout expires.
133 timeout <num> - wait for user input for <num>/10 seconds before
136 label <name> - begin a label definition. labels continue until
137 a command not recognized as a label command is seen,
140 Supported label commands
141 ------------------------
142 labels end when a command not recognized as a label command is reached, or EOF.
144 menu default - set this label as the default label to boot; this is
145 the same behavior as the global default command but
146 specified in a different way
148 kernel <path> - if this label is chosen, use tftp to retrieve the kernel
149 (or FIT image) at <path>. it will be stored at the address
150 indicated in the kernel_addr_r environment variable, and
151 that address will be passed to bootm to boot this kernel.
152 For FIT image, The configuration specification can be
153 appended to the file name, with the format:
154 <path>#<conf>[#<extra-conf[#...]]
155 It will passed to bootm with that address.
156 (see: doc/uImage.FIT/command_syntax_extensions.txt)
157 It useful for overlay selection in pxe file
158 (see: doc/uImage.FIT/overlay-fdt-boot.txt)
160 fdtoverlays <path> [...] - if this label is chosen, use tftp to retrieve the DT
161 overlay(s) at <path>. it will be temporarily stored at the
162 address indicated in the fdtoverlay_addr_r environment variable,
163 and then applied in the load order to the fdt blob stored at the
164 address indicated in the fdt_addr_r environment variable.
166 append <string> - use <string> as the kernel command line when booting this
169 initrd <path> - if this label is chosen, use tftp to retrieve the initrd
170 at <path>. it will be stored at the address indicated in
171 the initrd_addr_r environment variable, and that address
172 will be passed to bootm.
174 fdt <path> - if this label is chosen, use tftp to retrieve the fdt blob
175 at <path>. it will be stored at the address indicated in
176 the fdt_addr_r environment variable, and that address will
179 fdtdir <path> - if this label is chosen, use tftp to retrieve a fdt blob
180 relative to <path>. If the fdtfile environment variable
181 is set, <path>/<fdtfile> is retrieved. Otherwise, the
182 filename is generated from the soc and board environment
183 variables, i.e. <path>/<soc>-<board>.dtb is retrieved.
184 If the fdt command is specified, fdtdir is ignored.
186 localboot <flag> - Run the command defined by "localcmd" in the environment.
187 <flag> is ignored and is only here to match the syntax of
188 PXELINUX config files.
192 Here's a couple of example files to show how this works.
194 ------------/tftpboot/pxelinux.cfg/menus/base.menu-----------
195 menu title Linux selections
197 # This is the default label
199 menu label Default Install Image
200 kernel kernels/install.bin
201 append console=ttyAMA0,38400 debug earlyprintk
202 initrd initrds/uzInitrdDebInstall
206 kernel kernels/linux-2.6.38.bin
207 append root=/dev/sdb1
209 # The locally installed kernel
211 menu label Locally installed kernel
212 append root=/dev/sdb1
214 -------------------------------------------------------------
216 ------------/tftpboot/pxelinux.cfg/default-------------------
217 menu include pxelinux.cfg/menus/base.menu
221 -------------------------------------------------------------
223 When a pxe client retrieves and boots the default pxe file,
224 'pxe boot' will wait for user input for 5 seconds before booting
225 the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin
226 to be downloaded, and boot with the command line "root=/dev/sdb1"
228 Differences with PXELINUX
229 =========================
230 The biggest difference between U-Boot's pxe and PXELINUX is that since
231 U-Boot's pxe support is written entirely in C, it can run on any platform
232 with network support in U-Boot. Here are some other differences between
233 PXELINUX and U-Boot's pxe support.
235 - U-Boot's pxe does not support the PXELINUX DHCP option codes specified
236 in RFC 5071, but could be extended to do so.
238 - when U-Boot's pxe fails to boot, it will return control to U-Boot,
239 allowing another command to run, other U-Boot command, instead of resetting
240 the machine like PXELINUX.
242 - U-Boot's pxe doesn't rely on or provide an UNDI/PXE stack in memory, it
245 - U-Boot's pxe doesn't provide the full menu implementation that PXELINUX
246 does, only a simple text based menu using the commands described in
247 this README. With PXELINUX, it's possible to have a graphical boot
248 menu, submenus, passwords, etc. U-Boot's pxe could be extended to support
249 a more robust menuing system like that of PXELINUX's.
251 - U-Boot's pxe expects U-Boot uimg's as kernels. Anything that would work
252 with the 'bootm' command in U-Boot could work with the 'pxe boot' command.
254 - U-Boot's pxe only recognizes a single file on the initrd command line. It
255 could be extended to support multiple.
257 - in U-Boot's pxe, the localboot command doesn't necessarily cause a local
258 disk boot - it will do whatever is defined in the 'localcmd' env
259 variable. And since it doesn't support a full UNDI/PXE stack, the
260 type field is ignored.
262 - the interactive prompt in U-Boot's pxe only allows you to choose a label
263 from the menu. If you want to boot something not listed, you can ctrl+c
264 out of 'pxe boot' and use existing U-Boot commands to accomplish it.