Tiny PXE Server

ISO Images

ISO images can be difficult to boot via PXE. On BIOS systems, files loaded into memory (e.g. via memdisk or the Grub4dos map command) are implemented using INT 13h BIOS interrupt calls - as a consequence any operating systems that use real mode disk access (e.g. DOS) will still be able to access the (memory) loaded ISO. Operating systems that run in protected mode (e.g. Windows NT, Linux, etc) will no longer be able to access the loaded ISO once the protected mode kernel is running.

There are some exceptions to this -

"...The majority of Linux based CD images will also fail to work with MEMDISK ISO emulation. Linux distributions require kernel and initrd files to be specified, as soon as these files are loaded the protected mode kernel driver(s) take control and the virtual CD will no longer be accessible. If any other files are required from the CD/DVD they will be missing, resulting in boot error(s).

Linux distributions that only require kernel and initrd files function fully via ISO emulation, as no other data needs accessing from the virtual CD/DVD drive once they have been loaded. The boot loader has read all necessary files to memory by using INT 13h, before booting the kernel..."

FatDog ISO boot menu screenshot -

RAM based Windows Preinstallation Environments (WinPE) can also be loaded from ISO files - the initial stages of the boot process run in real mode, loading the required files (*.wim and *.sdi) into RAM > control is then passed to the kernel running in protected mode - preserving the memory mapped files due to WinPE's built in ramdisk driver. At this stage the ISO mapped to RAM is lost, however no further files are required from it so the boot process can complete successfully.

firadisk and winvblk are third party Windows RAM disk drivers capable of preserving mappings of files loaded into RAM via memdisk and the Grub4dos map command - if a Windows system contains these drivers then the ISO will still be accessible once the Operating System has loaded. If either of these drivers is correctly integrated into a Windows installation ISO file then it's possible to install Windows via a RAM loaded ISO file.

Three different methods for booting ISO files are covered in this document -

memdisk - loads the ISO file into memory prior to booting from it. Although it may no longer be possible to access the emulated disk (the iso mapped to memory) from the booted operating system if the kernel runs in protected mode, the RAM it occupies will remain in use - it's no longer available to the operating system. memdisk can be used in conjunction with iPXE to load an ISO file over HTTP - potentially loading the image much faster than when using TFTP.

grub4dos map command - operates in a similar manner to memdisk (see above) - particularly in terms of RAM not being available to the booted operating system.

SANBOOT - iPXE contains built in support for SANBOOT. This allows the ISO file on the server to be accessed directly - it's not loaded into memory first. As a consequence SANBOOT has clear advantages on systems with low RAM.

Quick note on ISO booting - if using iPXE then it's possible to boot ISO files from an external HTTP server - i.e. via the internet! There are two examples in the iPXE Scripts section of this page.

The following examples demonstrate booting from ISO files via PXE. Copy the following ISO files to C:\pxesrv\files\iso\ -

WinPE.iso (you will need to build your own WinPE as these files are non-redistributable)
Fatdog64-701.iso (from here)

Directory structure -

C:\pxesrv\files\iso\WinPE.iso
C:\pxesrv\files\iso\Fatdog64-701.iso

Now add a menu entry for your preferred Network Bootstrap Program -

pxelinux menu settings
grub4dos menu settings
iPXE menu settings
iPXE Scripts

pxelinux menu settings

Remember to ensure that the required files are copied to your Tiny PXE Server root directory -

C:\pxesrv\files\pxelinux.0
C:\pxesrv\files\memdisk
C:\pxesrv\files\menu.c32
C:\pxesrv\files\pxelinux.cfg\default

Add the following to C:\pxesrv\files\pxelinux.cfg\default (create this file if required) -
LABEL fdog_iso1 MENU LABEL FatDog64 (Memdisk) KERNEL memdisk append iso initrd=iso/Fatdog64-701.iso LABEL winpe_iso1 MENU LABEL WinPE (Memdisk) KERNEL memdisk append iso raw initrd=iso/WinPE.iso

Click on one of the following for sample config.ini settings (edit to reflect your own setup) -

DHCP - here
Proxy DHCP - here

grub4dos menu settings

Remember to ensure that the required files are copied to your Tiny PXE Server root directory -

C:\pxesrv\files\grldr
C:\pxesrv\files\memdisk
C:\pxesrv\files\menu.lst\default

Add the following to C:\pxesrv\files\menu.lst\default (create this file if required) -
title FatDog64 (MAP) map --mem (pd)/iso/Fatdog64-701.iso (0xFF) map --hook root (0xFF) chainloader (0xFF) title FatDog64 (Memdisk) kernel memdisk append iso initrd=iso/Fatdog64-701.iso title WinPE (MAP) map --mem (pd)/iso/WinPE.iso (0xFF) map --hook root (0xFF) chainloader (0xFF) title WinPE (Memdisk) kernel memdisk append iso raw initrd=iso/WinPE.iso

Click on one of the following for config.ini settings (edit to reflect your own setup) -

DHCP - here
Proxy DHCP - here

iPXE menu settings

Remember to ensure that the required files are copied to your Tiny PXE Server root directory -

C:\pxesrv\files\ipxe.pxe (or C:\pxesrv\files\ipxe-undionly.kpxe)
C:\pxesrv\files\ipxe_menu.txt
C:\pxesrv\files\memdisk

Screenshot (detail) of Fatdog64-701.iso being loaded into RAM using HTTP -

Add the following to the menu section of C:\pxesrv\files\ipxe_menu.txt (create this file if required) -
item fdog_iso1 FatDog64 (Memdisk) item fdog_iso2 FatDog64 (SANBOOT) item winpe_iso1 WinPE (Memdisk) item winpe_iso2 WinPE (SANBOOT)

Add the following to the menu options section of C:\pxesrv\files\ipxe_menu.txt -
:fdog_iso1 kernel ${boot-url}/memdisk iso raw initrd ${boot-url}/iso/Fatdog64-701.iso boot :fdog_iso2 sanboot --no-describe ${boot-url}/iso/Fatdog64-701.iso boot :winpe_iso1 kernel ${boot-url}/memdisk iso raw initrd ${boot-url}/iso/WinPE.iso boot :winpe_iso2 sanboot --no-describe ${boot-url}/iso/WinPE.iso boot

E.g. -
#!ipxe #============== Set Variables =============== set boot-url http://${dhcp-server} #================ Main Menu ================= menu iPXE boot menu item fdog_iso1 FatDog64 (Memdisk) item fdog_iso2 FatDog64 (SANBOOT) item winpe_iso1 WinPE (Memdisk) item winpe_iso2 WinPE (SANBOOT) choose target && goto ${target} #============ Main Menu Options ============= :fdog_iso1 kernel ${boot-url}/memdisk iso raw initrd ${boot-url}/iso/Fatdog64-701.iso boot :fdog_iso2 sanboot --no-describe ${boot-url}/iso/Fatdog64-701.iso boot :winpe_iso1 kernel ${boot-url}/memdisk iso raw initrd ${boot-url}/iso/WinPE.iso boot :winpe_iso2 sanboot --no-describe ${boot-url}/iso/WinPE.iso boot
NOTE - remember to change set boot-url http://${dhcp-server} if using ProxyDHCP.

Click on one of the following for config.ini settings (edit to reflect your own setup) -

DHCP - here
Proxy DHCP - here

iPXE Scripts

iPXE menus are essentially complicated scripts. It's also possible to specify a script using the altfilename option in config.ini. The two samples below can be used to boot ISO images over the internet.

Boot FatDog64 (version 7.01) from a web server - #!ipxe set boot-url http://${dhcp-server} kernel ${boot-url}/memdisk iso raw initrd http://distro.ibiblio.org/fatdog/iso/Fatdog64-701.iso boot

Boot Slitaz (version 4.0) from a web server - #!ipxe set boot-url http://${dhcp-server} kernel ${boot-url}/memdisk iso raw initrd http://mirror.slitaz.org/iso/4.0/slitaz-4.0.iso boot

Document date - 28^th February 2017(DRAFT)