xref: /openbmc/u-boot/doc/README.pxe (revision 1a68faac)
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
92pxe file format
93===============
94The pxe file format is nearly a subset of the PXELINUX file format; see
95http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed of one line
96commands - global commands, and commands specific to labels. Lines begining
97with # are treated as comments. White space between and at the beginning of
98lines is ignored.
99
100The size of pxe files and the number of labels is only limited by the amount
101of RAM available to U-Boot. Memory for labels is dynamically allocated as
102they're parsed, and memory for pxe files is statically allocated, and its
103location is given by the pxefile_addr_r environment variable. The pxe code is
104not aware of the size of the pxefile memory and will outgrow it if pxe files
105are too large.
106
107Supported global commands
108-------------------------
109Unrecognized commands are ignored.
110
111default <label>	    - the label named here is treated as the default and is
112		      the first label 'pxe boot' attempts to boot.
113
114menu title <string> - sets a title for the menu of labels being displayed.
115
116menu include <path> - use tftp to retrieve the pxe file at <path>, which
117		      is then immediately parsed as if the start of its
118		      contents were the next line in the current file. nesting
119		      of include up to 16 files deep is supported.
120
121prompt <flag>	    - if 1, always prompt the user to enter a label to boot
122		      from. if 0, only prompt the user if timeout expires.
123
124timeout <num>	    - wait for user input for <num>/10 seconds before
125		      auto-booting a node.
126
127label <name>	    - begin a label definition. labels continue until
128		      a command not recognized as a label command is seen,
129		      or EOF is reached.
130
131Supported label commands
132------------------------
133labels end when a command not recognized as a label command is reached, or EOF.
134
135menu default	    - set this label as the default label to boot; this is
136		      the same behavior as the global default command but
137		      specified in a different way
138
139kernel <path>	    - if this label is chosen, use tftp to retrieve the kernel
140		      (or FIT image) at <path>. it will be stored at the address
141		      indicated in the kernel_addr_r environment variable, and
142		      that address will be passed to bootm to boot this kernel.
143		      For FIT image, The configuration specification can be
144		      appended to the file name, with the format:
145		        <path>#<conf>[#<extra-conf[#...]]
146		      It will passed to bootm with that address.
147		      (see: doc/uImage.FIT/command_syntax_extensions.txt)
148		      It useful for overlay selection in pxe file
149		      (see: doc/uImage.FIT/overlay-fdt-boot.txt)
150
151append <string>	    - use <string> as the kernel command line when booting this
152		      label.
153
154initrd <path>	    - if this label is chosen, use tftp to retrieve the initrd
155		      at <path>. it will be stored at the address indicated in
156		      the initrd_addr_r environment variable, and that address
157		      will be passed to bootm.
158
159fdt <path>	    - if this label is chosen, use tftp to retrieve the fdt blob
160		      at <path>. it will be stored at the address indicated in
161		      the fdt_addr_r environment variable, and that address will
162		      be passed to bootm.
163
164fdtdir <path>	    - if this label is chosen, use tftp to retrieve a fdt blob
165		      relative to <path>. If the fdtfile environment variable
166		      is set, <path>/<fdtfile> is retrieved. Otherwise, the
167		      filename is generated from the soc and board environment
168		      variables, i.e. <path>/<soc>-<board>.dtb is retrieved.
169		      If the fdt command is specified, fdtdir is ignored.
170
171localboot <flag>    - Run the command defined by "localcmd" in the environment.
172		      <flag> is ignored and is only here to match the syntax of
173		      PXELINUX config files.
174
175Example
176-------
177Here's a couple of example files to show how this works.
178
179------------/tftpboot/pxelinux.cfg/menus/base.menu-----------
180menu title Linux selections
181
182# This is the default label
183label install
184	menu label Default Install Image
185	kernel kernels/install.bin
186	append console=ttyAMA0,38400 debug earlyprintk
187	initrd initrds/uzInitrdDebInstall
188
189# Just another label
190label linux-2.6.38
191	kernel kernels/linux-2.6.38.bin
192	append root=/dev/sdb1
193
194# The locally installed kernel
195label local
196	menu label Locally installed kernel
197	append root=/dev/sdb1
198	localboot 1
199-------------------------------------------------------------
200
201------------/tftpboot/pxelinux.cfg/default-------------------
202menu include pxelinux.cfg/menus/base.menu
203timeout 500
204
205default linux-2.6.38
206-------------------------------------------------------------
207
208When a pxe client retrieves and boots the default pxe file,
209'pxe boot' will wait for user input for 5 seconds before booting
210the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin
211to be downloaded, and boot with the command line "root=/dev/sdb1"
212
213Differences with PXELINUX
214=========================
215The biggest difference between U-Boot's pxe and PXELINUX is that since
216U-Boot's pxe support is written entirely in C, it can run on any platform
217with network support in U-Boot. Here are some other differences between
218PXELINUX and U-Boot's pxe support.
219
220- U-Boot's pxe does not support the PXELINUX DHCP option codes specified
221  in RFC 5071, but could be extended to do so.
222
223- when U-Boot's pxe fails to boot, it will return control to U-Boot,
224  allowing another command to run, other U-Boot command, instead of resetting
225  the machine like PXELINUX.
226
227- U-Boot's pxe doesn't rely on or provide an UNDI/PXE stack in memory, it
228  only uses U-Boot.
229
230- U-Boot's pxe doesn't provide the full menu implementation that PXELINUX
231  does, only a simple text based menu using the commands described in
232  this README.	With PXELINUX, it's possible to have a graphical boot
233  menu, submenus, passwords, etc. U-Boot's pxe could be extended to support
234  a more robust menuing system like that of PXELINUX's.
235
236- U-Boot's pxe expects U-Boot uimg's as kernels.  Anything that would work
237  with the 'bootm' command in U-Boot could work with the 'pxe boot' command.
238
239- U-Boot's pxe only recognizes a single file on the initrd command line.  It
240  could be extended to support multiple.
241
242- in U-Boot's pxe, the localboot command doesn't necessarily cause a local
243  disk boot - it will do whatever is defined in the 'localcmd' env
244  variable. And since it doesn't support a full UNDI/PXE stack, the
245  type field is ignored.
246
247- the interactive prompt in U-Boot's pxe only allows you to choose a label
248  from the menu.  If you want to boot something not listed, you can ctrl+c
249  out of 'pxe boot' and use existing U-Boot commands to accomplish it.
250