PXE Boot

Introduction

The Preboot eXecution Environment (PXE) is a technique that enables the distribution of arbitrary executable code or user data over the network. This can be used for example emergency systems or an Installation media without a USB stick.

Setup of a PXE server

The following software is required:

  • DHCP server (dhcpd, dnsmasq)
  • TFTP server (tftp-hpa, dnsmasq)
  • NFS server / HTTP server (nfs-server, nginx, darkhttpd)
  • Bootloader (syslinux)

The client to be booted must have a PXE-enabled network card. The PXE code will then first configure the interface via DHCP and gets the extended information like the TFTP server and bootloader file address. Afterwards the client can load the initial Network Bootstrap Program (NBP) and execute it in memory. A possible bootloader program is PXELinux.

sequenceDiagram
    participant C as PXE-Client
    participant S as DHCP-Server (PXE-fähig)
    participant T as TFTP-Server

    C->>+S: Extended DHCP Discover Port 67
    S-->>-C: Extended DHCP Offer Port 68
    C->>+S: DHCP Request Port 67
    S-->>-C: DHCP Boot Ack. Reply Port 68

    C->>+S: Boot Service Discover Port 67 oder 4011
    S-->>-C: Boot ServiceAck. Reply Port 67 oder 4011

    C->>+T: Bootstrap Program Download Request Port 69
    T-->>-C: Bootstrap Program Download Port 69

Proxy DHCP

Since the DHCP server is not always under the control of the developer, the Proxy DHCP solution is needed. In addition to the conventional DHCP exchange, supplementary information is sent from the Proxy DHCP Server.

Example Setup

In this example Syslinux is used directly from Archlinux ISO.

4 images are configured (2 times Archlinux, Clonezilla).

File structure

The ISO file is to be mounted, and then the necessary files are copied from it. The Syslinux folder becomes the root folder. Afterwards a directory is created in the root folder, where the images (e.g. Clonezilla, Archlinux etc.) should be stored.

tftp
├── hdt
├── images
│   ├── arch
│   │   ├── boot
│   │   │   ├── x86_64
│   │   │   │   ├── initramfs-linux.img
│   │   │   │   └── vmlinuz-linux
│   │   ├── x86_64
│   │   │   ├── airootfs.sfs
│   │   │   ├── airootfs.sfs.sig
│   │   │   └── airootfs.sha512
│   ├── archlinux-2021.06.01-x86_64.iso
│   └── clonezilla-live-2.7.2-39-amd64.iso
├── archiso_head.cfg
├── archiso_pxe.cfg
├── archiso_pxe-linux.cfg
├── archiso_sys.cfg
├── archiso_sys-linux.cfg
├── archiso_tail.cfg
├── lpxelinux.0
├── splash.png

DHCP Server

interface=vboxnet0
listen-address=192.168.56.1
dhcp-range=192.168.56.10,192.168.56.30,12h
dhcp-option-force=209,syslinux.cfg
dhcp-boot=lpxelinux.0
enable-tftp
tftp-root=/mnt/tftp
log-dhcp

Syslinux Config

syslinux.cfg

DEFAULT select

LABEL select
COM32 whichsys.c32
APPEND -pxe- pxe -sys- sys -iso- sys

LABEL pxe
CONFIG archiso_pxe.cfg

LABEL sys
CONFIG archiso_sys.cfg

archiso_pxe.cfg

INCLUDE archiso_head.cfg

INCLUDE archiso_pxe-linux.cfg

INCLUDE archiso_tail.cfg

archiso_head.cfg

SERIAL 0 115200
UI vesamenu.c32
MENU TITLE Arch Linux
MENU BACKGROUND splash.png

MENU WIDTH 78
MENU MARGIN 4
MENU ROWS 7
MENU VSHIFT 10
MENU TABMSGROW 14
MENU CMDLINEROW 14
MENU HELPMSGROW 16
MENU HELPMSGENDROW 29

# Refer to http://syslinux.zytor.com/wiki/index.php/Doc/menu

MENU COLOR border       30;44   #40ffffff #a0000000 std
MENU COLOR title        1;36;44 #9033ccff #a0000000 std
MENU COLOR sel          7;37;40 #e0ffffff #20ffffff all
MENU COLOR unsel        37;44   #50ffffff #a0000000 std
MENU COLOR help         37;40   #c0ffffff #a0000000 std
MENU COLOR timeout_msg  37;40   #80ffffff #00000000 std
MENU COLOR timeout      1;37;40 #c0ffffff #00000000 std
MENU COLOR msg07        37;40   #90ffffff #a0000000 std
MENU COLOR tabmsg       31;40   #30ffffff #00000000 std

MENU CLEAR
MENU IMMEDIATE

archiso_pxe-linux.cfg


# Entpacktes ISO, es wird ein HTTP Server benötigt
LABEL arch64_http
TEXT HELP
Boot the Arch Linux live medium using HTTP.
It allows you to install Arch Linux or perform system maintenance.
ENDTEXT
MENU LABEL Arch Linux install medium (x86_64, HTTP)
LINUX /images/arch/boot/x86_64/vmlinuz-linux
INITRD /images/arch/boot/intel-ucode.img,/images/arch/boot/amd-ucode.img,/images/arch/boot/x86_64/initramfs-linux.img
APPEND archisobasedir=/images/arch archiso_http_srv=http://${pxeserver}/ checksum verify
SYSAPPEND 3

# ISOs
LABEL arch-iso
LINUX memdisk
INITRD /images/archlinux-2021.06.01-x86_64.iso
APPEND iso

LABEL clonezilla-iso
LINUX memdisk
INITRD /images/clonezilla-live-2.7.2-39-amd64.iso
APPEND iso

archiso_tail.cfg

LABEL existing
TEXT HELP
Boot an existing operating system.
Press TAB to edit the disk and partition number to boot.
ENDTEXT
MENU LABEL Boot existing OS
COM32 chain.c32
APPEND hd0 0

# http://www.memtest.org/
LABEL memtest
MENU LABEL Run Memtest86+ (RAM test)
LINUX /arch/boot/memtest

# http://hdt-project.org/
LABEL hdt
MENU LABEL Hardware Information (HDT)
COM32 hdt.c32
APPEND modules_alias=hdt/modalias.gz pciids=hdt/pciids.gz

LABEL reboot
TEXT HELP
Reboot computer.
The computer's firmware must support APM.
ENDTEXT
MENU LABEL Reboot
COM32 reboot.c32

LABEL poweroff
TEXT HELP
Power off computer.
The computer's firmware must support APM.
ENDTEXT
MENU LABEL Power Off
COM32 poweroff.c32
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