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PXEBOOT(8) FreeBSD System Manager's Manual PXEBOOT(8)

Preboot Execution Environment (PXE) bootloader

The pxeboot bootloader is a modified version of the system third-stage bootstrap loader(8) configured to run under Intel's Preboot Execution Environment (PXE) system. PXE is a form of smart boot ROM, built into Intel EtherExpress Pro/100 and 3Com 3c905c Ethernet cards, and Ethernet-equipped Intel motherboards. PXE supports DHCP configuration and provides low-level NIC access services.
The DHCP client will set a DHCP user class named FreeBSD to allow flexible configuration of the DHCP server.
The pxeboot bootloader retrieves the kernel, modules, and other files either via NFS over UDP or by TFTP, selectable through compile-time options. In combination with a memory file system image or NFS-mounted root file system, pxeboot allows for easy, EEPROM-burner free construction of diskless machines.
The pxeboot binary is loaded just like any other boot file, by specifying it in the DHCP server's configuration file. Below is a sample configuration for the ISC DHCP v2 server:
option domain-name ""; 
option routers; 
option subnet-mask; 
option broadcast-address; 
option domain-name-servers; 
server-name "DHCPserver"; 
default-lease-time 120; 
max-lease-time 120; 
subnet netmask { 
       filename "pxeboot"; 
       if exists user-class and option user-class = "FreeBSD" { 
            option root-path "tftp://"; 

pxeboot recognizes next-server and option root-path directives as the server and path to NFS mount for file requests, respectively, or the server to make TFTP requests to. Note that pxeboot expects to fetch /boot/loader.rc from the specified server before loading any other files.
Valid option root-path Syntax is the following
path to the root filesystem on the NFS server
path to the root filesystem on the NFS server ip
path to the root filesystem on the NFS server
path to the root filesystem on the NFS server ip
path to the root filesystem on the TFTP server
path to the root filesystem on the TFTP server ip
pxeboot defaults to a conservative 1024 byte NFS data packet size. This may be changed by setting the nfs.read_size variable in /boot/loader.conf. Valid values range from 1024 to 16384 bytes.
In all other respects, pxeboot acts just like loader(8).
As PXE is still in its infancy, some firmware versions may not work properly. The pxeboot bootloader has been extensively tested on version 0.99 of Intel firmware; pre-release versions of the newer 2.0 firmware are known to have problems. Check with the device's manufacturer for their latest stable release.
For further information on Intel's PXE specifications and Wired for Management (WfM) systems, see


The pxeboot bootloader first appeared in FreeBSD 4.1.

The pxeboot bootloader was written by John Baldwin ⟨⟩ and Paul Saab ⟨⟩. This manual page was written by Doug White ⟨⟩.
May 27, 2017 FreeBSD 12.0-RELEASE

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