xref: /openbmc/u-boot/doc/README.pxe (revision 97e305cf)
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17
18The 'pxe' commands provide a near subset of the functionality provided by
19the PXELINUX boot loader. This allows U-boot based systems to be controlled
20remotely using the same PXE based techniques that many non U-boot based servers
21use.
22
23Commands
24========
25
26pxe get
27-------
28     syntax: pxe get
29
30     follows PXELINUX's rules for retrieving configuration files from a tftp
31     server, and supports a subset of PXELINUX's config file syntax.
32
33     Environment
34     -----------
35     'pxe get' requires two environment variables to be set:
36
37     pxefile_addr_r - should be set to a location in RAM large enough to hold
38     pxe files while they're being processed. Up to 16 config files may be
39     held in memory at once. The exact number and size of the files varies with
40     how the system is being used. A typical config file is a few hundred bytes
41     long.
42
43     bootfile,serverip - these two are typically set in the DHCP response
44     handler, and correspond to fields in the DHCP response.
45
46     'pxe get' optionally supports these two environment variables being set:
47
48     ethaddr - this is the standard MAC address for the ethernet adapter in use.
49     'pxe get' uses it to look for a configuration file specific to a system's
50     MAC address.
51
52     pxeuuid - this is a UUID in standard form using lower case hexadecimal
53     digits, for example, 550e8400-e29b-41d4-a716-446655440000. 'pxe get' uses
54     it to look for a configuration file based on the system's UUID.
55
56     File Paths
57     ----------
58     'pxe get' repeatedly tries to download config files until it either
59     successfully downloads one or runs out of paths to try. The order and
60     contents of paths it tries mirrors exactly that of PXELINUX - you can
61     read in more detail about it at:
62
63     http://syslinux.zytor.com/wiki/index.php/Doc/pxelinux
64
65pxe boot
66--------
67     syntax: pxe boot [pxefile_addr_r]
68
69     Interprets a pxe file stored in memory.
70
71     pxefile_addr_r is an optional argument giving the location of the pxe file.
72     The file must be terminated with a NUL byte.
73
74     Environment
75     -----------
76     There are some environment variables that may need to be set, depending
77     on conditions.
78
79     pxefile_addr_r - if the optional argument pxefile_addr_r is not supplied,
80     an environment variable named pxefile_addr_r must be supplied. This is
81     typically the same value as is used for the 'pxe get' command.
82
83     bootfile - typically set in the DHCP response handler based on the
84     same field in the DHCP respone, this path is used to generate the base
85     directory that all other paths to files retrieved by 'pxe boot' will use.
86     If no bootfile is specified, paths used in pxe files will be used as is.
87
88     serverip - typically set in the DHCP response handler, this is the IP
89     address of the tftp server from which other files will be retrieved.
90
91     kernel_addr_r, initrd_addr_r - locations in RAM at which 'pxe boot' will
92     store the kernel and initrd it retrieves from tftp. These locations will
93     be passed to the bootm command to boot the kernel. These environment
94     variables are required to be set.
95
96     fdt_addr - the location of a fdt blob. If this is set, it will be passed
97     to bootm when booting a kernel.
98
99pxe file format
100===============
101The pxe file format is nearly a subset of the PXELINUX file format; see
102http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed of one line
103commands - global commands, and commands specific to labels. Lines begining
104with # are treated as comments. White space between and at the beginning of
105lines is ignored.
106
107The size of pxe files and the number of labels is only limited by the amount
108of RAM available to U-boot. Memory for labels is dynamically allocated as
109they're parsed, and memory for pxe files is statically allocated, and its
110location is given by the pxefile_addr_r environment variable. The pxe code is
111not aware of the size of the pxefile memory and will outgrow it if pxe files
112are too large.
113
114Supported global commands
115-------------------------
116Unrecognized commands are ignored.
117
118default <label>	    - the label named here is treated as the default and is
119		      the first label 'pxe boot' attempts to boot.
120
121menu title <string> - sets a title for the menu of labels being displayed.
122
123menu include <path> - use tftp to retrieve the pxe file at <path>, which
124		      is then immediately parsed as if the start of its
125		      contents were the next line in the current file. nesting
126		      of include up to 16 files deep is supported.
127
128prompt <flag>	    - if 1, always prompt the user to enter a label to boot
129		      from. if 0, only prompt the user if timeout expires.
130
131timeout <num>	    - wait for user input for <num>/10 seconds before
132		      auto-booting a node.
133
134label <name>	    - begin a label definition. labels continue until
135		      a command not recognized as a label command is seen,
136		      or EOF is reached.
137
138Supported label commands
139------------------------
140labels end when a command not recognized as a label command is reached, or EOF.
141
142menu default	    - set this label as the default label to boot; this is
143		      the same behavior as the global default command but
144		      specified in a different way
145
146kernel <path>	    - if this label is chosen, use tftp to retrieve the kernel
147		      at <path>. it will be stored at the address indicated in
148		      the kernel_addr_r environment variable, and that address
149		      will be passed to bootm to boot this kernel.
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
159localboot <flag>    - Run the command defined by "localcmd" in the environment.
160		      <flag> is ignored and is only here to match the syntax of
161		      PXELINUX config files.
162
163Example
164-------
165Here's a couple of example files to show how this works.
166
167------------/tftpboot/pxelinux.cfg/menus/linux.list----------
168menu title Linux selections
169
170# This is the default label
171label install
172	menu label Default Install Image
173	kernel kernels/install.bin
174	append console=ttyAMA0,38400 debug earlyprintk
175	initrd initrds/uzInitrdDebInstall
176
177# Just another label
178label linux-2.6.38
179	kernel kernels/linux-2.6.38.bin
180	append root=/dev/sdb1
181
182# The locally installed kernel
183label local
184	menu label Locally installed kernel
185	append root=/dev/sdb1
186	localboot 1
187-------------------------------------------------------------
188
189------------/tftpboot/pxelinux.cfg/default-------------------
190menu include pxelinux.cfg/menus/base.menu
191timeout 500
192
193default linux-2.6.38
194-------------------------------------------------------------
195
196When a pxe client retrieves and boots the default pxe file,
197'pxe boot' will wait for user input for 5 seconds before booting
198the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin
199to be downloaded, and boot with the command line "root=/dev/sdb1"
200
201Differences with PXELINUX
202=========================
203The biggest difference between U-boot's pxe and PXELINUX is that since
204U-boot's pxe support is written entirely in C, it can run on any platform
205with network support in U-boot. Here are some other differences between
206PXELINUX and U-boot's pxe support.
207
208- U-boot's pxe does not support the PXELINUX DHCP option codes specified
209  in RFC 5071, but could be extended to do so.
210
211- when U-boot's pxe fails to boot, it will return control to U-boot,
212  allowing another command to run, other U-boot command, instead of resetting
213  the machine like PXELINUX.
214
215- U-boot's pxe doesn't rely on or provide an UNDI/PXE stack in memory, it
216  only uses U-boot.
217
218- U-boot's pxe doesn't provide the full menu implementation that PXELINUX
219  does, only a simple text based menu using the commands described in
220  this README.	With PXELINUX, it's possible to have a graphical boot
221  menu, submenus, passwords, etc. U-boot's pxe could be extended to support
222  a more robust menuing system like that of PXELINUX's.
223
224- U-boot's pxe expects U-boot uimg's as kernels.  Anything that would work
225  with the 'bootm' command in U-boot could work with the 'pxe boot' command.
226
227- U-boot's pxe only recognizes a single file on the initrd command line.  It
228  could be extended to support multiple.
229
230- in U-boot's pxe, the localboot command doesn't necessarily cause a local
231  disk boot - it will do whatever is defined in the 'localcmd' env
232  variable. And since it doesn't support a full UNDI/PXE stack, the
233  type field is ignored.
234
235- the interactive prompt in U-boot's pxe only allows you to choose a label
236  from the menu.  If you want to boot something not listed, you can ctrl+c
237  out of 'pxe boot' and use existing U-boot commands to accomplish it.
238