doc/README.pxe

   1 SPDX-License-Identifier: GPL-2.0+
   2 /*
   3  * Copyright 2010-2011 Calxeda, Inc.
   4  */
   5
   6 The 'pxe' commands provide a near subset of the functionality provided by
   7 the PXELINUX boot loader. This allows U-Boot based systems to be controlled
   8 remotely using the same PXE based techniques that many non U-Boot based servers
   9 use.
  10
  11 Commands
  12 ========
  13
  14 pxe 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
  53 pxe 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 pxe file format
  93 ===============
  94 The pxe file format is nearly a subset of the PXELINUX file format; see
  95 http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed of one line
  96 commands - global commands, and commands specific to labels. Lines begining
  97 with # are treated as comments. White space between and at the beginning of
  98 lines is ignored.
  99
 100 The size of pxe files and the number of labels is only limited by the amount
 101 of RAM available to U-Boot. Memory for labels is dynamically allocated as
 102 they're parsed, and memory for pxe files is statically allocated, and its
 103 location is given by the pxefile_addr_r environment variable. The pxe code is
 104 not aware of the size of the pxefile memory and will outgrow it if pxe files
 105 are too large.
 106
 107 Supported global commands
 108 -------------------------
 109 Unrecognized commands are ignored.
 110
 111 default <label>     - the label named here is treated as the default and is
 112                       the first label 'pxe boot' attempts to boot.
 113
 114 menu title <string> - sets a title for the menu of labels being displayed.
 115
 116 menu 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
 121 prompt <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
 124 timeout <num>       - wait for user input for <num>/10 seconds before
 125                       auto-booting a node.
 126
 127 label <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
 131 Supported label commands
 132 ------------------------
 133 labels end when a command not recognized as a label command is reached, or EOF.
 134
 135 menu 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
 139 kernel <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
 151 append <string>     - use <string> as the kernel command line when booting this
 152                       label.
 153
 154 initrd <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
 159 fdt <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
 164 fdtdir <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
 171 localboot <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
 175 Example
 176 -------
 177 Here's a couple of example files to show how this works.
 178
 179 ------------/tftpboot/pxelinux.cfg/menus/base.menu-----------
 180 menu title Linux selections
 181
 182 # This is the default label
 183 label 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
 190 label linux-2.6.38
 191         kernel kernels/linux-2.6.38.bin
 192         append root=/dev/sdb1
 193
 194 # The locally installed kernel
 195 label local
 196         menu label Locally installed kernel
 197         append root=/dev/sdb1
 198         localboot 1
 199 -------------------------------------------------------------
 200
 201 ------------/tftpboot/pxelinux.cfg/default-------------------
 202 menu include pxelinux.cfg/menus/base.menu
 203 timeout 500
 204
 205 default linux-2.6.38
 206 -------------------------------------------------------------
 207
 208 When a pxe client retrieves and boots the default pxe file,
 209 'pxe boot' will wait for user input for 5 seconds before booting
 210 the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin
 211 to be downloaded, and boot with the command line "root=/dev/sdb1"
 212
 213 Differences with PXELINUX
 214 =========================
 215 The biggest difference between U-Boot's pxe and PXELINUX is that since
 216 U-Boot's pxe support is written entirely in C, it can run on any platform
 217 with network support in U-Boot. Here are some other differences between
 218 PXELINUX 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.