2 * Copyright 2010-2011 Calxeda, Inc.
4 * SPDX-License-Identifier: GPL-2.0+
7 The 'pxe' commands provide a near subset of the functionality provided by
8 the PXELINUX boot loader. This allows U-boot based systems to be controlled
9 remotely using the same PXE based techniques that many non U-boot based servers
19 follows PXELINUX's rules for retrieving configuration files from a tftp
20 server, and supports a subset of PXELINUX's config file syntax.
24 'pxe get' requires two environment variables to be set:
26 pxefile_addr_r - should be set to a location in RAM large enough to hold
27 pxe files while they're being processed. Up to 16 config files may be
28 held in memory at once. The exact number and size of the files varies with
29 how the system is being used. A typical config file is a few hundred bytes
32 bootfile,serverip - these two are typically set in the DHCP response
33 handler, and correspond to fields in the DHCP response.
35 'pxe get' optionally supports these two environment variables being set:
37 ethaddr - this is the standard MAC address for the ethernet adapter in use.
38 'pxe get' uses it to look for a configuration file specific to a system's
41 pxeuuid - this is a UUID in standard form using lower case hexadecimal
42 digits, for example, 550e8400-e29b-41d4-a716-446655440000. 'pxe get' uses
43 it to look for a configuration file based on the system's UUID.
47 'pxe get' repeatedly tries to download config files until it either
48 successfully downloads one or runs out of paths to try. The order and
49 contents of paths it tries mirrors exactly that of PXELINUX - you can
50 read in more detail about it at:
52 http://syslinux.zytor.com/wiki/index.php/Doc/pxelinux
56 syntax: pxe boot [pxefile_addr_r]
58 Interprets a pxe file stored in memory.
60 pxefile_addr_r is an optional argument giving the location of the pxe file.
61 The file must be terminated with a NUL byte.
65 There are some environment variables that may need to be set, depending
68 pxefile_addr_r - if the optional argument pxefile_addr_r is not supplied,
69 an environment variable named pxefile_addr_r must be supplied. This is
70 typically the same value as is used for the 'pxe get' command.
72 bootfile - typically set in the DHCP response handler based on the
73 same field in the DHCP respone, this path is used to generate the base
74 directory that all other paths to files retrieved by 'pxe boot' will use.
75 If no bootfile is specified, paths used in pxe files will be used as is.
77 serverip - typically set in the DHCP response handler, this is the IP
78 address of the tftp server from which other files will be retrieved.
80 kernel_addr_r, initrd_addr_r - locations in RAM at which 'pxe boot' will
81 store the kernel and initrd it retrieves from tftp. These locations will
82 be passed to the bootm command to boot the kernel. These environment
83 variables are required to be set.
85 fdt_addr_r - location in RAM at which 'pxe boot' will store the fdt blob it
86 retrieves from tftp. The retrieval is possible if 'fdt' label is defined in
87 pxe file and 'fdt_addr_r' is set. If retrieval is possible, 'fdt_addr_r'
88 will be passed to bootm command to boot the kernel.
90 fdt_addr - the location of a fdt blob. 'fdt_addr' will be passed to bootm
91 command if it is set and 'fdt_addr_r' is not passed to bootm command.
95 The pxe file format is nearly a subset of the PXELINUX file format; see
96 http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed of one line
97 commands - global commands, and commands specific to labels. Lines begining
98 with # are treated as comments. White space between and at the beginning of
101 The size of pxe files and the number of labels is only limited by the amount
102 of RAM available to U-boot. Memory for labels is dynamically allocated as
103 they're parsed, and memory for pxe files is statically allocated, and its
104 location is given by the pxefile_addr_r environment variable. The pxe code is
105 not aware of the size of the pxefile memory and will outgrow it if pxe files
108 Supported global commands
109 -------------------------
110 Unrecognized commands are ignored.
112 default <label> - the label named here is treated as the default and is
113 the first label 'pxe boot' attempts to boot.
115 menu title <string> - sets a title for the menu of labels being displayed.
117 menu include <path> - use tftp to retrieve the pxe file at <path>, which
118 is then immediately parsed as if the start of its
119 contents were the next line in the current file. nesting
120 of include up to 16 files deep is supported.
122 prompt <flag> - if 1, always prompt the user to enter a label to boot
123 from. if 0, only prompt the user if timeout expires.
125 timeout <num> - wait for user input for <num>/10 seconds before
128 label <name> - begin a label definition. labels continue until
129 a command not recognized as a label command is seen,
132 Supported label commands
133 ------------------------
134 labels end when a command not recognized as a label command is reached, or EOF.
136 menu default - set this label as the default label to boot; this is
137 the same behavior as the global default command but
138 specified in a different way
140 kernel <path> - if this label is chosen, use tftp to retrieve the kernel
141 at <path>. it will be stored at the address indicated in
142 the kernel_addr_r environment variable, and that address
143 will be passed to bootm to boot this kernel.
145 append <string> - use <string> as the kernel command line when booting this
148 initrd <path> - if this label is chosen, use tftp to retrieve the initrd
149 at <path>. it will be stored at the address indicated in
150 the initrd_addr_r environment variable, and that address
151 will be passed to bootm.
153 fdt <path> - if this label is chosen, use tftp to retrieve the fdt blob
154 at <path>. it will be stored at the address indicated in
155 the fdt_addr_r environment variable, and that address will
158 localboot <flag> - Run the command defined by "localcmd" in the environment.
159 <flag> is ignored and is only here to match the syntax of
160 PXELINUX config files.
164 Here's a couple of example files to show how this works.
166 ------------/tftpboot/pxelinux.cfg/menus/linux.list----------
167 menu title Linux selections
169 # This is the default label
171 menu label Default Install Image
172 kernel kernels/install.bin
173 append console=ttyAMA0,38400 debug earlyprintk
174 initrd initrds/uzInitrdDebInstall
178 kernel kernels/linux-2.6.38.bin
179 append root=/dev/sdb1
181 # The locally installed kernel
183 menu label Locally installed kernel
184 append root=/dev/sdb1
186 -------------------------------------------------------------
188 ------------/tftpboot/pxelinux.cfg/default-------------------
189 menu include pxelinux.cfg/menus/base.menu
193 -------------------------------------------------------------
195 When a pxe client retrieves and boots the default pxe file,
196 'pxe boot' will wait for user input for 5 seconds before booting
197 the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin
198 to be downloaded, and boot with the command line "root=/dev/sdb1"
200 Differences with PXELINUX
201 =========================
202 The biggest difference between U-boot's pxe and PXELINUX is that since
203 U-boot's pxe support is written entirely in C, it can run on any platform
204 with network support in U-boot. Here are some other differences between
205 PXELINUX and U-boot's pxe support.
207 - U-boot's pxe does not support the PXELINUX DHCP option codes specified
208 in RFC 5071, but could be extended to do so.
210 - when U-boot's pxe fails to boot, it will return control to U-boot,
211 allowing another command to run, other U-boot command, instead of resetting
212 the machine like PXELINUX.
214 - U-boot's pxe doesn't rely on or provide an UNDI/PXE stack in memory, it
217 - U-boot's pxe doesn't provide the full menu implementation that PXELINUX
218 does, only a simple text based menu using the commands described in
219 this README. With PXELINUX, it's possible to have a graphical boot
220 menu, submenus, passwords, etc. U-boot's pxe could be extended to support
221 a more robust menuing system like that of PXELINUX's.
223 - U-boot's pxe expects U-boot uimg's as kernels. Anything that would work
224 with the 'bootm' command in U-boot could work with the 'pxe boot' command.
226 - U-boot's pxe only recognizes a single file on the initrd command line. It
227 could be extended to support multiple.
229 - in U-boot's pxe, the localboot command doesn't necessarily cause a local
230 disk boot - it will do whatever is defined in the 'localcmd' env
231 variable. And since it doesn't support a full UNDI/PXE stack, the
232 type field is ignored.
234 - the interactive prompt in U-boot's pxe only allows you to choose a label
235 from the menu. If you want to boot something not listed, you can ctrl+c
236 out of 'pxe boot' and use existing U-boot commands to accomplish it.