Ipxe Image For Mac

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  1. When I launch the virtual machine, it boots from the ISO image containing iPXE. IPXE initializes its network stack and proceeds to run the embedded script. Note how the chain command loads a script or image from the specified HTTP server and then boots into that.
  2. The process of booting a computer system over the network is well understood, and it’s been around for donkey’s ages. Basically, the way it works is that a computer system requests an IP address from a BOOTP/DHCP server, obtains the name of a bootstrap program (e.g. PXELINUX) it should load from a TFTP server, and subsequently uses that to boot the machine.

DHCP server setup¶

A DHCP server is required by PXE/iPXE client. You need to follow steps below.

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Aug 12, 2020 This option helps to isolate iPXE DHCP clients looking for an image to boot from a DHCP server. The following is sample DHCPv4 configuration from the ISC DHCP Server that displays the use of Option 77. The if condition in this sample implies that if Option 77 exists, and is equal to the string iPXE, then advertise the Boot File URI for the image. Name the file with the MAC address of the target host machine (01-macaddressoftargetESXihost), if only a specific host must boot this file. For example, 01-23-45-67-89-0a-bc. If your ESXi host runs UEFI firmware, copy the efi/boot/bootx64.efi file from the ESXi installer ISO image to the /tftpboot folder on your TFTP server, and rename the file to mboot.efi. When booting iPXE over the network on a Mac via the method described in the forum thread about Mac Pro (late 2013 model) EFI and iPXE booting (wrapping snponly.efi into a.nbi bundle and serving that via Apple's NetBoot/NetInstall service), one can chainload Linux kernels and EFI binaries just fine.

  1. Set the [dhcp]/dhcp_provider to neutron in the Bare Metal Service’sconfiguration file (/etc/ironic/ironic.conf):

    Note

    Refer Configure tenant networks for details. Thedhcp_provider configuration is already set by the configurationdefaults, and when you create subnet, DHCP is also enabled if you do not addany dhcp options at “openstack subnet create” command.

  2. Enable DHCP in the subnet of PXE network.

  3. Set the ip address range in the subnet for DHCP.

    Note

    Refer Configure the Networking service for bare metal provisioning for details about the twoprecedent steps.

  4. Connect the openstack DHCP agent to the external network through the OVSbridges and the interface eth2.

    Note

    Refer Configure the Networking service for bare metal provisioning for details. You do not requirethis part if br-int, br-eth2 and eth2 are already connected.

  5. Configure the host ip at br-eth2. If it locates at eth2, do below:

    Note

    Replace eth2 with the interface on the network node which you are using toconnect to the Bare Metal service.

The process of booting a computer system over the network is well understood,and it’s been around for donkey’s ages. Basically, the way it works is thata computer system requests an IP address from a BOOTP/DHCP server, obtains thename of a bootstrap program (e.g. PXELINUX) it should load from a TFTP server, and subsequentlyuses that to boot the machine. This is used extensively when installing operating systems onto a number of machines. I’ve been wanting to avoidusing TFTP because:

  • The first T in TFTP stands for trivial; TFTP is unreliable anderror-prone and won’t work over wide area networks. Ideally, PXEsystems would implement alternative protocols but most don’t.
  • TFTP is an all-or-nothing proposition: there’s no access control to thecontent of the server’s directory. (There is at least one server that includes libwrap capabilities.)
  • Configuration files for PXELINUX (i.e. the things that live in its pxelinux.cfgdirectory) cannot be created on demand. I can pre-create a file and save it in therequired directory for TFTP to send out, but files must exist by the timePXELINUX asks for them.

Earlier this year I mentioned I was setting up lots of bare metal, and Imentioned iPXE (formerly gPXE, formerly Etherboot).iPXE is a network boot loader which provides a full PXE implementationwith some exciting features: it can boot via HTTP (and from an iSCSI SAN), andI can control the boot process with a script. Ideally, the network cards (NIC)we use would have iPXE burnt in (which can be done) but in this project wehaven’t yet evaluated what that would mean in terms of hardware.

In the following discussion I assume you’ve downloaded a copy of the iPXE sourcecode and that you’ve have unpacked that and run a make in the src directory.This first make takes a bit of time; it creates all of iPXE’s target formats. Later onI’ll show you how to embed a script, and the make for that takes a second or two.

Three scenarios

iPXE can be used in a variety of ways, but I’ll concentrate on threescenarios in the following diagram:

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The three machines boot as follows:

  1. machine1 sends out a PXE request which is answered by a near-by DHCP server.It then loads iPXE as undionly.kpxe from the TFTP server, and the rest happens over HTTP.undionly.kpxe is created with makebin/undionly.kpxe, and I drop that file into my TFTP root directory and then have myDHCP server give this file as boot file to my clients, ensuring I break theinfinite loop that would result. (My dhcpd.conf is below.)

  2. machine2 boots with a customized iPXE script, either from a modifiednetwork ROM or via, say, a CD-ROM. It obtains its network address via DHCPand can then directly “speak” to a HTTP server.To create a customized boot loader with an embedded script (e.g.jpmens.ipxe), I invoke make bin/undionly.kpxe EMBED=jpmens.ipxe andstore the resulting file on a bootable floppy or burn it onto a CD-ROM,etc. The embedded script uses a iPXE commands to obtain DHCP parameterswhen it starts, or I can hard-code IP address, net mask, etc., and I can useiPXE settings in the script, as we’ll see for machine3.

  3. In the case of machine3, I’ve created a custom iPXE image with whichthe machine boots. The script contains hard-coded network addresses, and itshould be straight-forward to mass-create custom images with a bit of sh and make.This is interesting if there is no DHCP server (or relay) close to (network-wise) the node.

DHCP, TFTP, and HTTP

machine1 uses DHCP and a TFTP server to load iPXE’s undionly.kpxe, afterwhich the latter takes over. The DHCP server configuration I’m using is:

When the machine (node) boots it fires off its first PXE request, our DHCP serverreceives the request and gives it an IP address, netmask, etc. as well as aboot filename undionly.kpxe. The node then retrieves undionly.kpxe via TFTPand loads and executes it. iPXE (undionly.kpxe) then again issues a DHCPrequest. Without the if exists user-class magic we’d enter an endless loop whereiPXE would load itself, then load itself, ad nauseam. The if ensures that when iPXEissues a DHCP request, it is given the filename called netboot.php which resideson a HTTP server. From this point onwards, everything happens over HTTP!

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The file name iPXE chains into is an HTTP URL which, in my case, creates anon-the-fly configuration script for iPXE. (The strange-looking concat business in dhcpd.conf is to ensure the hardware address is correctly formatted.)To make things easier, I’llomit showing the code the iPXE script is generated from (basically a databaseaccess and some Mustache); instead, here is its output:

The echo prints information to the screen, using some of iPXE’ssettings. Apart from that, a kernel is loaded together withan initrd image, and we attempt to boot that. If that fails, wefall back into iPXE’s shell.

Statically dynamic

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The configuration for machine2 and machine3 differ only slightly in thatthe former lets iPXE obtain network parameters via DHCP, and the latter has themembedded in the script. I can test with a VirtualBox client which bootsfrom an ISO image created with one of the iPXEmake targets. What Idid was to create a script called jpstatic.ipxe and I then built the ISOimage I attached to VirtualBox with

Mac

The file jpstatic.ipxe is an iPXE script which defines network addressesfor the machine and subsequently chains to the boot file.

When I launch the virtual machine, it boots from the ISO image containing iPXE.iPXE initializes its network stack and proceeds to run the embedded script. Notehow the chain command loads a script or image from the specified HTTP serverand then boots into that.

The node.ipxe script I’m chaining into doesn’t do much except print out someiPXE’s variable values obtained via DHCP or hardcoded into the script,and it then launches the iPXE shell:

From the iPXE shell, I can chain into whatever I want to, say, the demo image. I enter the chain command with the URL, the kernel and initrd are loaded from the iPXE HTTP server and it is booted:

PXELINUX over HTTP

To be as flexible as possible with regard to booting different types of images,allowing boot menus, etc. I’m adding a level of indirection. PXELINUX versions >= 3.70 can boot over HTTP. (I tried withthe latest version (4.04) but that failed, so I fell back to using version 3.86.)I installed nasm and built the code from a SYSLINUX distribution:

Take note that I’m copying pxelinux.0 to the HTTP document root, and not theTFTP root. I then changed my netboot.php to return the following iPXEscript:

The two DHCP options define the HTTP URL to the root of the HTTP server (209)and to the configuration file for PXELINUX (210) respectively. Without option209, when PXELINUX is loaded it will attempt to retrieve its configuration (viaHTTP) from the following URLS:

Instead of using static files I create PXELINUX configuration on the fly. For example, if pxelinux.php outputs

the node would boot Centos, whereas if it, instead, output

then the machine boots from the first hard disk. It is important to realizethat all paths I’ve used (e.g. bootmsg.txt, centos/vmlinuz, chain.c32(also from SYSLINUX)) are relative to the HTTP root we specified as option 210above. (Keep an eye on your HTTP access log when experimenting with this.)

dnsmasq as a DHCP server

If you use dnsmasq as your DHCP server, you can also do this. Here’sa snippet from my dnsmasq.conf:

Summary

To summarize, I need a DHCP server and a TFTP server close by the machines(nodes) I’ll be booting this way, unless I go the extra mile and create customundionly.kpxe images that can be booted from local media. When nodes boot they go through the following chain of events:

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  1. Machine boots.
    1. If configured to use local boot media, loads iPXE from that.
    2. Otherwise:
      1. Hardware does a PXE boot and sends out a DHCP request.
      2. DHCP server returns reply and boot filename undionly.kpxe.
      3. Node requests file from TFTP server.
  2. undionly.kpxe (iPXE) loads and optionally issues another DHCP request, and then
  3. chains (boots) into the script returned by netboot.php.
  4. Node loads pxelinux.0 via HTTP.
  5. pxelinux.0 loads configuration file specified in option 209. (pxelinux.php)
  6. pxelinux.0 loads further kernel via HTTP depending on configuration.

This sounds quite convoluted, and it is rather, but we gain a lot offunctionality:

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  • Nodes can boot over the WAN links (e.g. the Internet).
  • If necessary, we can use caching HTTP proxies to reduce the volume of data transferred from the deployment server to groups of nodes.
  • We can apply granular access-controls to the HTTP server, something very difficult (or impossible?) to do with TFTP.
  • We are highly flexible in how we create configuration for clients; we can usedatabase queries to provision boot scripts to individual nodes or groups ofnodes.

  • Client nodes can be set to always PXE boot, and we can remote-control what theydo when they’re power-cycled: install, boot from disk, show menu, etc.