doc/README.pxe

   1 /*
   2  * Copyright 2010-2011 Calxeda, Inc.
   3  *
   4  * SPDX-License-Identifier:     GPL-2.0+
   5  */
   6
   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
  10 use.
  11
  12 Commands
  13 ========
  14
  15 pxe get
  16 -------
  17      syntax: pxe get
  18
  19      follows PXELINUX's rules for retrieving configuration files from a tftp
  20      server, and supports a subset of PXELINUX's config file syntax.
  21
  22      Environment
  23      -----------
  24      'pxe get' requires two environment variables to be set:
  25
  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
  30      long.
  31
  32      bootfile,serverip - these two are typically set in the DHCP response
  33      handler, and correspond to fields in the DHCP response.
  34
  35      'pxe get' optionally supports these two environment variables being set:
  36
  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
  39      MAC address.
  40
  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.
  44
  45      File Paths
  46      ----------
  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:
  51
  52      http://syslinux.zytor.com/wiki/index.php/Doc/pxelinux
  53
  54 pxe boot
  55 --------
  56      syntax: pxe boot [pxefile_addr_r]
  57
  58      Interprets a pxe file stored in memory.
  59
  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.
  62
  63      Environment
  64      -----------
  65      There are some environment variables that may need to be set, depending
  66      on conditions.
  67
  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.
  71
  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.
  76
  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.
  79
  80      kernel_addr_r, initrd_addr_r - locations in RAM at which 'pxe boot' will
  81      store the kernel(or FIT image) and initrd it retrieves from tftp. These
  82      locations will be passed to the bootm command to boot the kernel. These
  83      environment variables are required to be set.
  84
  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.
  89
  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.
  92
  93 pxe file format
  94 ===============
  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
  99 lines is ignored.
 100
 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
 106 are too large.
 107
 108 Supported global commands
 109 -------------------------
 110 Unrecognized commands are ignored.
 111
 112 default <label>     - the label named here is treated as the default and is
 113                       the first label 'pxe boot' attempts to boot.
 114
 115 menu title <string> - sets a title for the menu of labels being displayed.
 116
 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.
 121
 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.
 124
 125 timeout <num>       - wait for user input for <num>/10 seconds before
 126                       auto-booting a node.
 127
 128 label <name>        - begin a label definition. labels continue until
 129                       a command not recognized as a label command is seen,
 130                       or EOF is reached.
 131
 132 Supported label commands
 133 ------------------------
 134 labels end when a command not recognized as a label command is reached, or EOF.
 135
 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
 139
 140 kernel <path>       - if this label is chosen, use tftp to retrieve the kernel
 141                       (or FIT image) at <path>. it will be stored at the address
 142                       indicated in the kernel_addr_r environment variable, and
 143                       that address will be passed to bootm to boot this kernel.
 144
 145 append <string>     - use <string> as the kernel command line when booting this
 146                       label.
 147
 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.
 152
 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
 156                       be passed to bootm.
 157
 158 fdtdir <path>       - if this label is chosen, use tftp to retrieve a fdt blob
 159                       relative to <path>. If the fdtfile environment variable
 160                       is set, <path>/<fdtfile> is retrieved. Otherwise, the
 161                       filename is generated from the soc and board environment
 162                       variables, i.e. <path>/<soc>-<board>.dtb is retrieved.
 163                       If the fdt command is specified, fdtdir is ignored.
 164
 165 localboot <flag>    - Run the command defined by "localcmd" in the environment.
 166                       <flag> is ignored and is only here to match the syntax of
 167                       PXELINUX config files.
 168
 169 Example
 170 -------
 171 Here's a couple of example files to show how this works.
 172
 173 ------------/tftpboot/pxelinux.cfg/menus/base.menu-----------
 174 menu title Linux selections
 175
 176 # This is the default label
 177 label install
 178         menu label Default Install Image
 179         kernel kernels/install.bin
 180         append console=ttyAMA0,38400 debug earlyprintk
 181         initrd initrds/uzInitrdDebInstall
 182
 183 # Just another label
 184 label linux-2.6.38
 185         kernel kernels/linux-2.6.38.bin
 186         append root=/dev/sdb1
 187
 188 # The locally installed kernel
 189 label local
 190         menu label Locally installed kernel
 191         append root=/dev/sdb1
 192         localboot 1
 193 -------------------------------------------------------------
 194
 195 ------------/tftpboot/pxelinux.cfg/default-------------------
 196 menu include pxelinux.cfg/menus/base.menu
 197 timeout 500
 198
 199 default linux-2.6.38
 200 -------------------------------------------------------------
 201
 202 When a pxe client retrieves and boots the default pxe file,
 203 'pxe boot' will wait for user input for 5 seconds before booting
 204 the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin
 205 to be downloaded, and boot with the command line "root=/dev/sdb1"
 206
 207 Differences with PXELINUX
 208 =========================
 209 The biggest difference between U-Boot's pxe and PXELINUX is that since
 210 U-Boot's pxe support is written entirely in C, it can run on any platform
 211 with network support in U-Boot. Here are some other differences between
 212 PXELINUX and U-Boot's pxe support.
 213
 214 - U-Boot's pxe does not support the PXELINUX DHCP option codes specified
 215   in RFC 5071, but could be extended to do so.
 216
 217 - when U-Boot's pxe fails to boot, it will return control to U-Boot,
 218   allowing another command to run, other U-Boot command, instead of resetting
 219   the machine like PXELINUX.
 220
 221 - U-Boot's pxe doesn't rely on or provide an UNDI/PXE stack in memory, it
 222   only uses U-Boot.
 223
 224 - U-Boot's pxe doesn't provide the full menu implementation that PXELINUX
 225   does, only a simple text based menu using the commands described in
 226   this README.  With PXELINUX, it's possible to have a graphical boot
 227   menu, submenus, passwords, etc. U-Boot's pxe could be extended to support
 228   a more robust menuing system like that of PXELINUX's.
 229
 230 - U-Boot's pxe expects U-Boot uimg's as kernels.  Anything that would work
 231   with the 'bootm' command in U-Boot could work with the 'pxe boot' command.
 232
 233 - U-Boot's pxe only recognizes a single file on the initrd command line.  It
 234   could be extended to support multiple.
 235
 236 - in U-Boot's pxe, the localboot command doesn't necessarily cause a local
 237   disk boot - it will do whatever is defined in the 'localcmd' env
 238   variable. And since it doesn't support a full UNDI/PXE stack, the
 239   type field is ignored.
 240
 241 - the interactive prompt in U-Boot's pxe only allows you to choose a label
 242   from the menu.  If you want to boot something not listed, you can ctrl+c
 243   out of 'pxe boot' and use existing U-Boot commands to accomplish it.