Learning to Boot from PXE

I've used PXE (not even iPXE, just DHCP/TFTP without HTTP) mainly in environments where a LAN client-server game would need to be launched on many systems at once. Nothing quite like rolling out a hand-tailored distro for a single game to 16 computers and seeing them all boot and load straight into the game, one after the other, entirely unattended, from one broadcast boot-over-Ethernet trigger.

I think at one point we were even using distcc to use the clients to speed up rebuilds while iterating on the game. I should revisit that with iPXE and icecream.

Oh oh oh I know this!

I work in the refurb division of an ewaste recycling company[0]. To prepare a machine for sale, the drive needs to be wiped, and (optionally) an OS loaded. Wiping happens in WipeOS[1], which loads when you PXE boot on the internal company network. To install an OS, I have a separate network on my desk that will load iVentoy[2] when PXE booted, where I can further boot from ISOs I have on my server, but I almost always install Linux Mint. With those 2 things, I can largely do my job without fumbling with and losing USB drives.

I have 2 16 port switches on my desk, with over a dozen ethernet cables plugged into each. The yellow cables will PXE boot WipeOS, and the black ones PXE boot iVentoy.

[0] https://www.ebay.com/str/evolutionecycling

[1] https://www.wipeos.com/

[2] https://www.iventoy.com/en/index.html

PXE is awesome, especially if you combine it with systemd's UKI mechanism and its EFI stub. You can load a single file via TFTP or HTTP(S) and boot into a read-only (or ramdisk-only) full Linux system. Most off the shelf distributions can be made to work in this way, with a small bit of effort. A very usable Debian system is a few hundred MB.

You can extend this with secure boot (using your own keys) to sign the entire UKI file, so your firmware will authenticate the full "disk" image that it boots into.

Lots of fun with this and lots of possibilities.

Had great experience using PXE to boot HPC farms, mounting the OS from a NAS and using only a local disk in the machine for tmp and other writable locations. I am not sure how 'diskless' linux works these days on rocky flavours but was solid in centos 5 through 7.

The fun thing about learning to boot from PXE, is that you have to learn it every time you onboard a new type of hardware... or a new VM hypervisor... or new NIC firmware... or new BIOS firmware.

God help you if you actually want to install an operating system.

PXE is such a vital capability for working with on-prem servers. But it's ten different things which all have to play nicely together. Every time I build a PXE system I feel like I'm reinventing the universe in my tiny subnet.

TFTP is crazy slow, even with RFC 7740 (buffering), but the payloads are usually small so few people care.

Thankfully modern BIOSes tend to implement HTTP boot option, where you can point to any HTTP or HTTPS URL (as long as the URL ends with ".efi", which is a pretty dumb limitation if you ask me).