Provisioning Linux Using PXELINUX

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Provisioning Linux UsingPXELINUX

• Scott Mewett
• Rackable Systems
• Linux World Solutions Summit 2007
• February 15, 2007

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Agenda

• What is PXELINUX
• What PXELINUX is not
• Requirements
• Booting Process
• Config files
• COMBOOT and COM32
• memdisk
• memtest86
• Setting up - DHCP, TFTP
• Demo
• Questions

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Quote

• PXELINUX is really cool
• - Scott Mewett Just Now

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What is PXELINUX

• SYSLINUX is for booting Linux from a FAT file
  system
• ISOLINUX is for booting Linux ISO 9660 CDs
• Therefore PXELINUX is the counterpart for booting
  Linux and other operating systems from network
  servers.

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What PXELINUX is not

• Not Linux - It helps you to boot Linux
• In fact it can be used for booting OSs other
  than Linux
• Not a boot ROM. It requires PXE support for your
  NIC

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Requirements

• PXE Compliant network adapter
• DHCP Server with the following options
• next-server
• Filename
• If using Option 43 and a PXE Daemon, then also
  add vendor-class-identifier PXEClient
• TFTP Server
• on your tftp server
• pxelinux.0, config files, menu files,
• kernel and ram disks you want to boot

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Booting Process

• A PXE boot is initiated either by adjusting the
  BIOS boot order selecting network boot during
  POST
• Network adapter starts PXE Boot and requests DHCP
  address.
• DHCP response has IP information ip, netmask,
  gateway, dns server, PLUS
• next-server 192.168.1.5
• filename /tftpboot/pxelinux.0
• Client configures network adapter using dhcp info
• Client requests filename /tftpboot/pxelinux.0
  from next-server 192.168.1.5 via tftp.
• pxelinux.0 is executed and starts requesting
  config files from tftp server

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Booting Process - cont

• First requests config file name based after the
  MAC address the client used to boot. i.e.
  /tftpboot/pxelinux.cfg/01-00-0a-0b-0c-12-13
• If not found then it will search for the config
  file using its own IP address in upper case
  hexadecimal
• e.g. 192.168.1.100 -gt C0A80164
• If that file is not found, it will remove one hex
  digit and try again
• Ultimately it will try looking for a file called
  default in lowercase
• All filename references are relative to the
  directory that pxelinux.0 lives in
• Config file is processed and any menu is
  displayed
• Client selects boot option to boot. Kernel and
  ram disk are downloaded from the same tftp server
  and kernel is executed.

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Standard Config file

• Uses syslinux syntax
• Instead of files being located on a dos file
  system, they are downloaded from the tftp server.
• First section defines global settings
• default linux
• prompt 1
• timeout 600
• display boot.msg
• F1 boot.msg
• The rest is made up of boot options
• Boot options start with a label definition
• label linux
• kernel rhel/3/u6/vmlinuz
• append initrdrhel/3/u6/initrd.img
  ramdisk_size8192
• ipappend 2

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Standard Config file - Cool options

• IPAPPEND 2
• Addes BOOTIFltMACADDRgt to kernel append line
• Files can be organized on your tftp server in
  directories.
• Kernels can be in one dir, initrds in another,
  and menus in yet another
• Kernels and initrds can be on an alternate tftp
  server.
• 192.168.1.6/images/rhel/3/u6/vmlinuz
• tftp1.foo.com/images/rhel/3/u6/vmlinuz
• LOCALBOOT
• Boot from local disk
• Great if you have BIOS pxeboot by default, then
  on timeout you can have it localboot

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COMBOOT and COM32

• SYSLINUX supports simple standalone programs,
  using a file format similar to DOS ".com" files.
• A 32-bit version, called COM32, is also provided.
  A simple API provides access to a limited set of
  file system and console functions.
• For info on writing your own see http//syslinu
  x.zytor.com/comboot.php
• Interesting example of COM32 put into practice
• http//people.cs.uchicago.edu/gmurali/gui/autoboo
  t.html

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Cool COM32 programs

• menu.c32
• Simple menu system
• Uses standard syslinux syntax plus more but
  starts with
• default menu.c32
• prompt 0
• Supports serial console
• Menu items can reference other menu files
• label othermenu
• menu label Other Menu
• kernel menu.c32
• append othermenu.conf

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Cool COM32 Programs - cont

• mboot.c32
• Allows booting of kernels that use the multiboot
  standard
• i.e. Xen
• LABEL Xen
• KERNEL mboot.c32
• APPEND xen.gz dom0_mem15000 nosmp noacpi ---
  linux.gz consoletty0 root/dev/hda1 ---
  initrd.img
• chain.c32
• chainload another operating system on a hard disk
• label windows
• kernel chain.c32
• append hd0 2

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memdisk - booting dos

• Memdisk which is part of SYSLINUX can be used to
  boot dos floppy images
• Create bootable dos floppy
• dd it to a file.
• Then boot it using pxelinux and memdisk
• label dos
• kernel memdisk
• append initrddosfloppy.img
• keeppxe
• Keeppxe will keep the PXE and UNDI stacks in
  memory so that DOS can use it.

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memtest86

• Memtest86 is thorough, stand alone memory test
  for x86 architecture computers
• Download it from www.memtest86.com
• Boot it with pxelinux like so
• label memtest
• kernel memtest86
• append -

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Setting up - DHCP

• ISC DHCP supports lots of great options for PXE
• See lots of examples here http//syslinux.zytor.
  com/pxe.phpdhcp
• You at least need options next-server and
  filename
• If using option 43, you must have option 60 set
  to PXEClient
• Older bios work with out it, but Broadcom
  recently fixed this so now its required as
  according to spec.

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Setting up - TFTP

• Great tftp server is hpa-tftp available from
  kernel.org
• Written by author of PXELINUX
• Create /tftpboot
• Put pxelinux.0 in /tftpboot
• Create /tftpboot/pxelinux.cfg and put config
  files in there.
• Create symlink of /tftpboot/tftpboot to .
• ln -s . /tftpboot/tftpboot
• This way /tftpboot/pxelinux.0 and pxelinux.0 are
  valid ways of requesting the same file

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• Demo

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• Questions?

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• Contact info
• Scott Mewett
• smewett_at_rackable.com