[maccam912]

Since I won't get a better chance to find knowledgeable people: How exactly does iPXE work? Lets say I want to boot a random old PC from one of these images - does the bios need to have iPXE support? Or PXE? Or does it need to first boot into some local system first, which then goes out and gets the image to boot the rest of the way from?

Then there's mention of DHCP and self hosting. Do I need to have some service running within my LAN first or can this go right out to some public server and boot from images there? How does DHCP factor in? I am in so far over my head on this but it seems interesting and something fun to try out.

[NobodyNada]

PXE [0] is a standard for netbooting, typically implementated in the system's boot firmware. A PXE-compatible client sends a DHCP request on boot, to which the network's DHCP server responds with the IP address of a server to netboot from. The client will then connect to this server via TFTP, download an executable image file in the PXE format, and boot it. Using PXE on your own computer requires enabling PXE the firmware setup, setting up a TFTP server to serve the PXE image, and configuring your DHCP server to point to your TFTP server.

iPXE [1] is an open-source implementation of PXE, and much more -- it's much more flexible, it supports additional protocols including HTTP(S) and DNS, it has configuration and scripting options, a basic command-line interface, etc. In order to run iPXE, you need to boot an iPXE image somehow -- e.g. from a MBR or EFI image on a disk drive or USB drive (or even over PXE, I guess). But because iPXE supports more protocols and more configuration, you don't need to set up TFTP and DHCP, and it can chainload into e.g. an EFI image or a Linux kernel instead of being limited to booting images in the PXE format.

An example of iPXE in the wild is the Arch Linux netboot image [2]. They provide pre-configured iPXE images that display an interactive menu to select a mirror, download the Arch Linux installer, and boot it. (It's really convenient since you can just drop the UEFI image at "/efi/boot/bootx64.efi" on a FAT32 thumb drive instead of having to download the whole installer image and 'dd' it onto the drive.)

The submitted project, netboot.xyz, is a similar idea: a preconfigured build of iPXE that lets you interactively download and boot installers for many popular operating systems from a single image.

[0]: https://en.wikipedia.org/wiki/Preboot_Execution_Environment

[1]: https://ipxe.org/

[2]: https://archlinux.org/releng/netboot/

[throw0101d]

> A PXE-compatible client sends a DHCP request on boot, to which the network's DHCP server responds with the IP address of a server to netboot from.

Specifically there are particular DHCP options (66, 67) that tell the client about this, and the client software (PXE) understands them:

* https://datatracker.ietf.org/doc/html/rfc2132

* https://www.iana.org/assignments/bootp-dhcp-parameters/bootp...

* https://www.iana.org/assignments/dhcpv6-parameters/dhcpv6-pa... (RFC 5970)

And while the options previously were interpreted for TFTP use, newer PXE software now understands the use of "http[s]://" in the file name and use that instead of TFTP.

[ddulaney]

> or even over PXE, I guess

This is super common actually! Most built-in PXE only supports TFTP, which is pretty slow compared to TCP-based stuff. It can make sense to use the built-in PXE to grab a (small) iPXE image over TFTP, then have iPXE grab the (big) real image over HTTP(S). This is also useful if you want to store your main image on something like S3 that doesn’t support TFTP.

For a while I had a script that would create iPXE images dynamically on the fly with the correct HTTPS URL and auth information embedded in them.

[scoot]

> it can chainload into e.g. an EFI image

Off topic, but does anyone know a good resource that explains how to correctly use "e.g."? (I've looked before, but didn't find one)

While I may seem like a grammar pedant, there are many things that have entered common use while arguably incorrect that I'm not so bothered about ("That begs the question", for example). However while this (incorrect) use of "e.g." is a hill I will die on, even so, I struggle to explain why it's just plain wrong. (It can be used to replace "for example" when preceding a list if examples that illustrate a point, but not as a generic replacement as in this case.)

Someone somewhere must have explained it better...

[teo_zero]

> while this (incorrect) use of "e.g." is a hill I will die on, even so, I struggle to explain why it's just plain wrong.

Are there many such things you would die for without even knowing why? :)

"Exempli gratia" translates quite literally to "for the sake of example". I see no grammatical reasons why you shouldn't use it as the GP used it.

Are you sure you are not mistaking e.g. with i.e.? The latter stands for "id est" and means "that is", but the two are often confounded, and it's not unusual to find i.e. used to introduce an example. If the GP had used i.e., that would be a hill to die on.

[scoot]

> Are there many such things you would die for without even knowing why?

I didn't say I don't know why. I said that finding good reference material to explain it is hard to find.

> Are you sure you are not mistaking e.g. with i.e.?

Yes, I'm sure. I'm surprise that if you know the difference, you don't know the correct usage.

[sakjur]

Chicago Manual of Style [6.51, 5.250], though I'd argue this is pedantry for casual conversation. From 6.51: "[...]Note that in formal writing, Chicago prefers to confine the abbreviations i.e. ("that is") and e.g. ("for example") to parentheses or notes, where they are followed by a comma".

I think a secondary argument could be made that i.e. and e.g. are typically used to clarify something in a second clause; e.g., "it can chainload into any form of boot image (e.g., an EFI image or a Linux kernel) rather than being restricted to the PXE image format".

I would recommend picking up a copy of CMOS if you are in want of good ways to explain English grammar. English is my secondary language, and it's occasionally helpful for me to have access to a reference for its grammar when I struggle with understanding a concept. Just keep in mind that languages are bendable and any guide is descriptive and not prescriptive for informal communication.

[scoot]

Belated upvote for answering the question, in contrast to the many who downvoted because they don't understand how to use "e.g." correctly, and were too lazy to find out.

[ac29]

> It can be used to replace "for example" when preceding a list if examples that illustrate a point

I think you've already understood it.

[scoot]

I think so too, but many references fail to explain it in a way that isn't ambiguous at best.

[ddulaney]

Is this wrong? I always mentally replace "e.g." with "for example" (so this sentence is "it can chainload into, for example, an EFI image"). That sounds right to me. This seems like somebody doing it right :)

[scoot]

Yes, it wrong. "e.g." isn't a direct substitute for "for example". Honestly, it's best avoided as so many people confuse "e.g." and "i.e.", but if you're going to use it, at least use it correctly.

[hmaxwell]

You can use netboot.xyz from a flash drive to boot various operating systems and utilities. Alternatively, PXE (Preboot Execution Environment) has been around for a while and works by allowing a network-capable device to boot from its network interface. A PXE-compatible network card requests a DHCP lease during the boot process, which provides the IP address of a TFTP (Trivial File Transfer Protocol) server and the file that needs to be loaded from the server.

Typically, the network card contains a basic PXE kernel. To enhance this environment, you can chainload iPXE, which offers a broader range of features. iPXE allows for more advanced booting options, such as loading scripts or initiating an unattended installation directly from the network.

[RulerOf]

Since nobody directly answered some of your specific questions:

> Lets say I want to boot a random old PC from one of these images - does the bios need to have iPXE support? Or PXE?

The most-desirable way to use iPXE is to boot it from a system's built-in PXE, chainloading it from a local DCHP+TFTP server. All routers have a DHCP server, and many enthusiast/professional routers will have a TFTP server available. pfSense/OPNSense for example can both do this.

If you want to go down the rabbit hole and can mod your system BIOS, you can install iPXE into many of them. I wouldn't recommend it, but I did it once and thought it was pretty cool.

> random old PC

If you _literally_ meant like a vintage PC that predates the PXE spec[1], you can boot iPXE from any local media — I architected a project 10 years ago where I actually gave floppy disks to technicians because some of the ancient Dells we were working with required a BIOS update to enable USB booting.

You can also burn iPXE into a network card's ROM chip. There were a lot of PCI/ISA network cards that took an EEPROM and could boot from them if populated. I always thought it would be fun to boot a vintage PC with iPXE straight off of an add-in network card like that. iPXE will hook the BIOS, and you can literally boot MS-DOS via iSCSI.

> Do I need to have some service running within my LAN first or can this go right out to some public server and boot from images there?

Again, typical deployments will have iPXE chainloaded from the system's existing PXE implementation, which means you've got a DHCP server on the local segment, and a TFTP server somewhere on the local network. But you _could_ boot iPXE from any other boot medium, which would mean the DHCP/TFTP setup are not required. iPXE itself, once loaded, can do its work with any network connection.

[1]: https://en.wikipedia.org/wiki/Wired_for_Management - this happened in 1998/1999 and implementation was widespread by 2001 or so.

[mynameisvlad]

There's multiple ways to boot, including USB/ISO: https://netboot.xyz/docs/category/booting-methods

Generally speaking, if you have iPXE already compiled and flashed onto your NIC, then you can follow these instructions: https://netboot.xyz/docs/booting/ipxe

DHCP is only needed for getting an IP address. You can use the Docker image with the proper DHCP parameters to load it automatically when using PXE/iPXE: https://netboot.xyz/docs/docker

[anon291]

So what I do here is that I have a local PXE server (it's a DHCP option on your router) that serves up iPXE with a preconfigured script to boot via HTTP off of netboot.xyz. So whenever I want to install linux on a new computer, I set the BIOS boot option to boot from PXE next boot and restart. In a few seconds, I am presented with my choice of linux environment.

For my data center servers, I have it booting via PXE to an iPXE with a custom script to take a unique identifier from the host and build the corresponding configuration (NixOS). So essentially for that I define my NixOS configuration in a NixOS flake and plug the new host in and it will boot to the correct configuration. I actually don't have any OS installation on most of the hosts and share the nix store via NFS.

I also keep an iPXE thumb drive around in case I need to do this for something not on my network. In that case, I insert the drive, boot from it, and then ask it to boot from netboot.xyz manually.

[teraflop]

There are a bunch of different options to "bootstrap" iPXE in the first place. Least invasive is probably to boot it from a USB drive. You can also set up a traditional PXE boot process using DHCP/TFTP on your network to "chain-load" iPXE (if your client's network card supports PXE), or you can even flash iPXE into the boot ROM on certain network cards.

However you do it, once iPXE starts running, it will take control of the NIC and fetch the actual OS images that it needs from the internet over HTTP.

[Joe_Cool]

Some HP server UEFIs also support boot from http. So you can boot the .efi executable directly from the internet. For https you need to enroll the certificate first and it's a bit more involved.

I am sure there are other implementations I have only seen it on HP servers so far.

[breppp]

Roughly from memory iPXE is a bootable image that acts similar to a PXE BIOS, so you boot to that image like a regular disk. It acts like a bios by for example hooking your interrupts for storage reads.

In order to find where the image is, you need some kind of discovery mechanism. This is where DHCP comes in. Remember this is all happening before you have an OS, so it has to be very bare bones

[alfiedotwtf]

If you want to see how all the magic happens, have a look at the code and docs from Debian’s FAI (Fully Automated Install). Once you have a Debian FAI all setup, you can bootstrap your machine from zero every morning while you have your morning coffee

[gsich]

You usually chainload from normal PXE if you have hardware.

[bongodongobob]

Read the docs, it's all there.

Edit: Seriously? You click on docs and almost all of those questions are answered. It's 1 click away. Parent didn't even try.

[notanormalnerd]

I found the netboot docs very hard to understand if you dont have a existing knowledge of PXE.

[bongodongobob]

Has HN turned into a Facebook group?

[LoganDark]

Which docs? The netboot.xyz ones?

[bongodongobob]

Yes. It's one click away for the overview and the quick start is very good as well.

[LoganDark]

That's great if you want a tutorial, I guess. "How does this work" is different from a tutorial though, IMHO.