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"Das U-Boot" Source Tree
1SPDX-License-Identifier: GPL-2.0+
2/*
3 * Copyright 2010-2011 Calxeda, Inc.
4 */
5
6The 'pxe' commands provide a near subset of the functionality provided by
7the PXELINUX boot loader. This allows U-Boot based systems to be controlled
8remotely using the same PXE based techniques that many non U-Boot based servers
9use.
10
11Commands
12========
13
14pxe get
15-------
16 syntax: pxe get
17
18 follows PXELINUX's rules for retrieving configuration files from a tftp
19 server, and supports a subset of PXELINUX's config file syntax.
20
21 Environment
22 -----------
23 'pxe get' requires two environment variables to be set:
24
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
29 long.
30
31 bootfile,serverip - these two are typically set in the DHCP response
32 handler, and correspond to fields in the DHCP response.
33
34 'pxe get' optionally supports these two environment variables being set:
35
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
38 MAC address.
39
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.
43
44 File Paths
45 ----------
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:
50
51 http://syslinux.zytor.com/wiki/index.php/Doc/pxelinux
52
53pxe boot
54--------
55 syntax: pxe boot [pxefile_addr_r]
56
57 Interprets a pxe file stored in memory.
58
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.
61
62 Environment
63 -----------
64 There are some environment variables that may need to be set, depending
65 on conditions.
66
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.
70
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.
75
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.
78
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.
83
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.
88
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.
91
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'.
94
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.
100
101pxe file format
102===============
103The pxe file format is nearly a subset of the PXELINUX file format; see
104http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed of one line
105commands - global commands, and commands specific to labels. Lines begining
106with # are treated as comments. White space between and at the beginning of
107lines is ignored.
108
109The size of pxe files and the number of labels is only limited by the amount
110of RAM available to U-Boot. Memory for labels is dynamically allocated as
111they're parsed, and memory for pxe files is statically allocated, and its
112location is given by the pxefile_addr_r environment variable. The pxe code is
113not aware of the size of the pxefile memory and will outgrow it if pxe files
114are too large.
115
116Supported global commands
117-------------------------
118Unrecognized commands are ignored.
119
120default <label> - the label named here is treated as the default and is
121 the first label 'pxe boot' attempts to boot.
122
123fallback <label> - the label named here is treated as a fallback option that
124 may be attempted should it be detected that booting of
125 the default has failed to complete, for example via
126 U-Boot's boot count limit functionality.
127
128menu title <string> - sets a title for the menu of labels being displayed.
129
130menu include <path> - use tftp to retrieve the pxe file at <path>, which
131 is then immediately parsed as if the start of its
132 contents were the next line in the current file. nesting
133 of include up to 16 files deep is supported.
134
135prompt <flag> - if 1, always prompt the user to enter a label to boot
136 from. if 0, only prompt the user if timeout expires.
137
138timeout <num> - wait for user input for <num>/10 seconds before
139 auto-booting a node.
140
141label <name> - begin a label definition. labels continue until
142 a command not recognized as a label command is seen,
143 or EOF is reached.
144
145Supported label commands
146------------------------
147labels end when a command not recognized as a label command is reached, or EOF.
148
149menu default - set this label as the default label to boot; this is
150 the same behavior as the global default command but
151 specified in a different way
152
153kernel <path> - if this label is chosen, use tftp to retrieve the kernel
154 (or FIT image) at <path>. it will be stored at the address
155 indicated in the kernel_addr_r environment variable, and
156 that address will be passed to bootm to boot this kernel.
157 For FIT image, The configuration specification can be
158 appended to the file name, with the format:
159 <path>#<conf>[#<extra-conf[#...]]
160 It will passed to bootm with that address.
161 (see: doc/uImage.FIT/command_syntax_extensions.txt)
162 It useful for overlay selection in pxe file
163 (see: doc/uImage.FIT/overlay-fdt-boot.txt)
164
165fdtoverlays <path> [...] - if this label is chosen, use tftp to retrieve the DT
166 overlay(s) at <path>. it will be temporarily stored at the
167 address indicated in the fdtoverlay_addr_r environment variable,
168 and then applied in the load order to the fdt blob stored at the
169 address indicated in the fdt_addr_r environment variable.
170
171devicetree-overlay <path> [...] - if this label is chosen, use tftp to retrieve the DT
172 overlay(s) at <path>. it will be temporarily stored at the
173 address indicated in the fdtoverlay_addr_r environment variable,
174 and then applied in the load order to the fdt blob stored at the
175 address indicated in the fdt_addr_r environment variable.
176 Alias for fdtoverlays.
177
178kaslrseed - set this label to request random number from hwrng as kaslr seed.
179
180append <string> - use <string> as the kernel command line when booting this
181 label.
182
183initrd <path> - if this label is chosen, use tftp to retrieve the initrd
184 at <path>. it will be stored at the address indicated in
185 the initrd_addr_r environment variable, and that address
186 will be passed to bootm.
187 For FIT image, the initrd can be provided with the same value than
188 kernel, including configuration:
189 <path>#<conf>[#<extra-conf[#...]]
190 In this case, kernel_addr_r is passed to bootm.
191
192fdt <path> - if this label is chosen, use tftp to retrieve the fdt blob
193 at <path>. it will be stored at the address indicated in
194 the fdt_addr_r environment variable, and that address will
195 be passed to bootm.
196 For FIT image, the device tree can be provided with the same value
197 than kernel, including configuration:
198 <path>#<conf>[#<extra-conf[#...]]
199 In this case, kernel_addr_r is passed to bootm.
200
201devicetree <path> - if this label is chosen, use tftp to retrieve the fdt blob
202 at <path>. it will be stored at the address indicated in
203 the fdt_addr_r environment variable, and that address will
204 be passed to bootm. Alias for fdt.
205
206fdtdir <path> - if this label is chosen, use tftp to retrieve a fdt blob
207 relative to <path>. If the fdtfile environment variable
208 is set, <path>/<fdtfile> is retrieved. Otherwise, the
209 filename is generated from the soc and board environment
210 variables, i.e. <path>/<soc>-<board>.dtb is retrieved.
211 If the fdt command is specified, fdtdir is ignored.
212
213localboot <flag> - Run the command defined by "localcmd" in the environment.
214 <flag> is ignored and is only here to match the syntax of
215 PXELINUX config files.
216
217Example
218-------
219Here's a couple of example files to show how this works.
220
221------------/tftpboot/pxelinux.cfg/menus/base.menu-----------
222menu title Linux selections
223
224# This is the default label
225label install
226 menu label Default Install Image
227 kernel kernels/install.bin
228 append console=ttyAMA0,38400 debug earlyprintk
229 initrd initrds/uzInitrdDebInstall
230
231# Just another label
232label linux-2.6.38
233 kernel kernels/linux-2.6.38.bin
234 append root=/dev/sdb1
235
236# The locally installed kernel
237label local
238 menu label Locally installed kernel
239 append root=/dev/sdb1
240 localboot 1
241-------------------------------------------------------------
242
243------------/tftpboot/pxelinux.cfg/default-------------------
244menu include pxelinux.cfg/menus/base.menu
245timeout 500
246
247default linux-2.6.38
248-------------------------------------------------------------
249
250When a pxe client retrieves and boots the default pxe file,
251'pxe boot' will wait for user input for 5 seconds before booting
252the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin
253to be downloaded, and boot with the command line "root=/dev/sdb1"
254
255Differences with PXELINUX
256=========================
257The biggest difference between U-Boot's pxe and PXELINUX is that since
258U-Boot's pxe support is written entirely in C, it can run on any platform
259with network support in U-Boot. Here are some other differences between
260PXELINUX and U-Boot's pxe support.
261
262- U-Boot's pxe does not support the PXELINUX DHCP option codes specified
263 in RFC 5071, but could be extended to do so.
264
265- when U-Boot's pxe fails to boot, it will return control to U-Boot,
266 allowing another command to run, other U-Boot command, instead of resetting
267 the machine like PXELINUX.
268
269- U-Boot's pxe doesn't rely on or provide an UNDI/PXE stack in memory, it
270 only uses U-Boot.
271
272- U-Boot's pxe doesn't provide the full menu implementation that PXELINUX
273 does, only a simple text based menu using the commands described in
274 this README. With PXELINUX, it's possible to have a graphical boot
275 menu, submenus, passwords, etc. U-Boot's pxe could be extended to support
276 a more robust menuing system like that of PXELINUX's.
277
278- U-Boot's pxe expects U-Boot uimg's as kernels. Anything that would work
279 with the 'bootm' command in U-Boot could work with the 'pxe boot' command.
280
281- U-Boot's pxe only recognizes a single file on the initrd command line. It
282 could be extended to support multiple.
283
284- in U-Boot's pxe, the localboot command doesn't necessarily cause a local
285 disk boot - it will do whatever is defined in the 'localcmd' env
286 variable. And since it doesn't support a full UNDI/PXE stack, the
287 type field is ignored.
288
289- the interactive prompt in U-Boot's pxe only allows you to choose a label
290 from the menu. If you want to boot something not listed, you can ctrl+c
291 out of 'pxe boot' and use existing U-Boot commands to accomplish it.