uboot/doc/README.pxe
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   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
  95pxe file format
  96===============
  97The pxe file format is nearly a subset of the PXELINUX file format; see
  98http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed of one line
  99commands - global commands, and commands specific to labels. Lines begining
 100with # are treated as comments. White space between and at the beginning of
 101lines is ignored.
 102
 103The size of pxe files and the number of labels is only limited by the amount
 104of RAM available to U-Boot. Memory for labels is dynamically allocated as
 105they're parsed, and memory for pxe files is statically allocated, and its
 106location is given by the pxefile_addr_r environment variable. The pxe code is
 107not aware of the size of the pxefile memory and will outgrow it if pxe files
 108are too large.
 109
 110Supported global commands
 111-------------------------
 112Unrecognized commands are ignored.
 113
 114default <label>     - the label named here is treated as the default and is
 115                      the first label 'pxe boot' attempts to boot.
 116
 117menu title <string> - sets a title for the menu of labels being displayed.
 118
 119menu include <path> - use tftp to retrieve the pxe file at <path>, which
 120                      is then immediately parsed as if the start of its
 121                      contents were the next line in the current file. nesting
 122                      of include up to 16 files deep is supported.
 123
 124prompt <flag>       - if 1, always prompt the user to enter a label to boot
 125                      from. if 0, only prompt the user if timeout expires.
 126
 127timeout <num>       - wait for user input for <num>/10 seconds before
 128                      auto-booting a node.
 129
 130label <name>        - begin a label definition. labels continue until
 131                      a command not recognized as a label command is seen,
 132                      or EOF is reached.
 133
 134Supported label commands
 135------------------------
 136labels end when a command not recognized as a label command is reached, or EOF.
 137
 138menu default        - set this label as the default label to boot; this is
 139                      the same behavior as the global default command but
 140                      specified in a different way
 141
 142kernel <path>       - if this label is chosen, use tftp to retrieve the kernel
 143                      (or FIT image) at <path>. it will be stored at the address
 144                      indicated in the kernel_addr_r environment variable, and
 145                      that address will be passed to bootm to boot this kernel.
 146                      For FIT image, The configuration specification can be
 147                      appended to the file name, with the format:
 148                        <path>#<conf>[#<extra-conf[#...]]
 149                      It will passed to bootm with that address.
 150                      (see: doc/uImage.FIT/command_syntax_extensions.txt)
 151                      It useful for overlay selection in pxe file
 152                      (see: doc/uImage.FIT/overlay-fdt-boot.txt)
 153
 154fdtoverlays <path> [...] - if this label is chosen, use tftp to retrieve the DT
 155                      overlay(s) at <path>. it will be temporarily stored at the
 156                      address indicated in the fdtoverlay_addr_r environment variable,
 157                      and then applied in the load order to the fdt blob stored at the
 158                      address indicated in the fdt_addr_r environment variable.
 159
 160append <string>     - use <string> as the kernel command line when booting this
 161                      label.
 162
 163initrd <path>       - if this label is chosen, use tftp to retrieve the initrd
 164                      at <path>. it will be stored at the address indicated in
 165                      the initrd_addr_r environment variable, and that address
 166                      will be passed to bootm.
 167
 168fdt <path>          - if this label is chosen, use tftp to retrieve the fdt blob
 169                      at <path>. it will be stored at the address indicated in
 170                      the fdt_addr_r environment variable, and that address will
 171                      be passed to bootm.
 172
 173fdtdir <path>       - if this label is chosen, use tftp to retrieve a fdt blob
 174                      relative to <path>. If the fdtfile environment variable
 175                      is set, <path>/<fdtfile> is retrieved. Otherwise, the
 176                      filename is generated from the soc and board environment
 177                      variables, i.e. <path>/<soc>-<board>.dtb is retrieved.
 178                      If the fdt command is specified, fdtdir is ignored.
 179
 180localboot <flag>    - Run the command defined by "localcmd" in the environment.
 181                      <flag> is ignored and is only here to match the syntax of
 182                      PXELINUX config files.
 183
 184Example
 185-------
 186Here's a couple of example files to show how this works.
 187
 188------------/tftpboot/pxelinux.cfg/menus/base.menu-----------
 189menu title Linux selections
 190
 191# This is the default label
 192label install
 193        menu label Default Install Image
 194        kernel kernels/install.bin
 195        append console=ttyAMA0,38400 debug earlyprintk
 196        initrd initrds/uzInitrdDebInstall
 197
 198# Just another label
 199label linux-2.6.38
 200        kernel kernels/linux-2.6.38.bin
 201        append root=/dev/sdb1
 202
 203# The locally installed kernel
 204label local
 205        menu label Locally installed kernel
 206        append root=/dev/sdb1
 207        localboot 1
 208-------------------------------------------------------------
 209
 210------------/tftpboot/pxelinux.cfg/default-------------------
 211menu include pxelinux.cfg/menus/base.menu
 212timeout 500
 213
 214default linux-2.6.38
 215-------------------------------------------------------------
 216
 217When a pxe client retrieves and boots the default pxe file,
 218'pxe boot' will wait for user input for 5 seconds before booting
 219the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin
 220to be downloaded, and boot with the command line "root=/dev/sdb1"
 221
 222Differences with PXELINUX
 223=========================
 224The biggest difference between U-Boot's pxe and PXELINUX is that since
 225U-Boot's pxe support is written entirely in C, it can run on any platform
 226with network support in U-Boot. Here are some other differences between
 227PXELINUX and U-Boot's pxe support.
 228
 229- U-Boot's pxe does not support the PXELINUX DHCP option codes specified
 230  in RFC 5071, but could be extended to do so.
 231
 232- when U-Boot's pxe fails to boot, it will return control to U-Boot,
 233  allowing another command to run, other U-Boot command, instead of resetting
 234  the machine like PXELINUX.
 235
 236- U-Boot's pxe doesn't rely on or provide an UNDI/PXE stack in memory, it
 237  only uses U-Boot.
 238
 239- U-Boot's pxe doesn't provide the full menu implementation that PXELINUX
 240  does, only a simple text based menu using the commands described in
 241  this README.  With PXELINUX, it's possible to have a graphical boot
 242  menu, submenus, passwords, etc. U-Boot's pxe could be extended to support
 243  a more robust menuing system like that of PXELINUX's.
 244
 245- U-Boot's pxe expects U-Boot uimg's as kernels.  Anything that would work
 246  with the 'bootm' command in U-Boot could work with the 'pxe boot' command.
 247
 248- U-Boot's pxe only recognizes a single file on the initrd command line.  It
 249  could be extended to support multiple.
 250
 251- in U-Boot's pxe, the localboot command doesn't necessarily cause a local
 252  disk boot - it will do whatever is defined in the 'localcmd' env
 253  variable. And since it doesn't support a full UNDI/PXE stack, the
 254  type field is ignored.
 255
 256- the interactive prompt in U-Boot's pxe only allows you to choose a label
 257  from the menu.  If you want to boot something not listed, you can ctrl+c
 258  out of 'pxe boot' and use existing U-Boot commands to accomplish it.
 259