One Boot Config to Rule Them All: Bringing UAPI Boot Specification to Legacy BIOS (asg2025)

The UAPI Boot Loader Specification defines conventions that let multiple operating systems and bootloaders share boot config files. So far, only systemd-boot implements it - and it’s UEFI-only by design. As a result, hybrid UEFI/BIOS images require maintaining (and keeping in sync) two sets of bootloader configs: one for systemd-boot, and one for a legacy bootloader such as syslinux. I set out to fix that by building a BIOS bootloader that uses the UAPI Boot Loader Specification - allowing both UEFI and legacy boot to use a single shared set of config files. This talk is about why that matters, how I built it, and what comes next. In this talk, I’ll cover: - What the UAPI boot spec is - Why you'd want to use legacy boot instead of EFI/systemd-boot - *spoiler: you don't! but you might have to* - How I implemented UAPI boot support for legacy BIOS - What about UKIs? - A live demo of the bootloader in action - The current state of the project and what’s next https://uapi-group.org/specifications/specs/boot_loader_specification https://github.com/nkraetzschmar/bootloader Licensed to the public under https://creativecommons.org/licenses/by/4.0/de/ about this event: https://cfp.all-systems-go.io/all-systems-go-2025/talk/ANC879/