1/* 2 * Copyright 2010-2011 Calxeda, Inc. 3 * 4 * SPDX-License-Identifier: GPL-2.0+ 5 */ 6 7The 'pxe' commands provide a near subset of the functionality provided by 8the PXELINUX boot loader. This allows U-Boot based systems to be controlled 9remotely using the same PXE based techniques that many non U-Boot based servers 10use. 11 12Commands 13======== 14 15pxe 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 54pxe 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 and initrd it retrieves from tftp. These locations will 82 be passed to the bootm command to boot the kernel. These environment 83 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 93pxe file format 94=============== 95The pxe file format is nearly a subset of the PXELINUX file format; see 96http://syslinux.zytor.com/wiki/index.php/PXELINUX. It's composed of one line 97commands - global commands, and commands specific to labels. Lines begining 98with # are treated as comments. White space between and at the beginning of 99lines is ignored. 100 101The size of pxe files and the number of labels is only limited by the amount 102of RAM available to U-Boot. Memory for labels is dynamically allocated as 103they're parsed, and memory for pxe files is statically allocated, and its 104location is given by the pxefile_addr_r environment variable. The pxe code is 105not aware of the size of the pxefile memory and will outgrow it if pxe files 106are too large. 107 108Supported global commands 109------------------------- 110Unrecognized commands are ignored. 111 112default <label> - the label named here is treated as the default and is 113 the first label 'pxe boot' attempts to boot. 114 115menu title <string> - sets a title for the menu of labels being displayed. 116 117menu 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 122prompt <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 125timeout <num> - wait for user input for <num>/10 seconds before 126 auto-booting a node. 127 128label <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 132Supported label commands 133------------------------ 134labels end when a command not recognized as a label command is reached, or EOF. 135 136menu 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 140kernel <path> - if this label is chosen, use tftp to retrieve the kernel 141 at <path>. it will be stored at the address indicated in 142 the kernel_addr_r environment variable, and that address 143 will be passed to bootm to boot this kernel. 144 145append <string> - use <string> as the kernel command line when booting this 146 label. 147 148initrd <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 153fdt <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 158fdtdir <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 165localboot <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 169Example 170------- 171Here's a couple of example files to show how this works. 172 173------------/tftpboot/pxelinux.cfg/menus/base.menu----------- 174menu title Linux selections 175 176# This is the default label 177label 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 184label linux-2.6.38 185 kernel kernels/linux-2.6.38.bin 186 append root=/dev/sdb1 187 188# The locally installed kernel 189label local 190 menu label Locally installed kernel 191 append root=/dev/sdb1 192 localboot 1 193------------------------------------------------------------- 194 195------------/tftpboot/pxelinux.cfg/default------------------- 196menu include pxelinux.cfg/menus/base.menu 197timeout 500 198 199default linux-2.6.38 200------------------------------------------------------------- 201 202When a pxe client retrieves and boots the default pxe file, 203'pxe boot' will wait for user input for 5 seconds before booting 204the linux-2.6.38 label, which will cause /tftpboot/kernels/linux-2.6.38.bin 205to be downloaded, and boot with the command line "root=/dev/sdb1" 206 207Differences with PXELINUX 208========================= 209The biggest difference between U-Boot's pxe and PXELINUX is that since 210U-Boot's pxe support is written entirely in C, it can run on any platform 211with network support in U-Boot. Here are some other differences between 212PXELINUX 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. 244