NixOS on ARM/UEFI

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Note: The page is written assuming AArch64. It is possible that following most of these instructions for armv7l would work just as well, but armv7l support in NixOS is not at a point where doing so will be nice.

This section of the NixOS on ARM documentation aims to document as much as possible about booting any ARM boards using UEFI.

The Basics First

Target Support

Some things will not be specific to UEFI. For example, board support by the kernel used. This is written assuming that mainline Linux works enough on the target system so that you can install from the generic iso image.

Just as you could on x86_64 if your platform required it, you can build a customized iso image. Explaining this is out of scope for this article. The same pitfalls apply. For example, the generated configuration will not take into account configuring the customized kernel.

Initial Boot Firmware

Let's define what an Initial Boot Firmware is. It is a generic term I'm using to describe the first thing the CPU starts at boot time. On your typical x86_64 system, it would be what was previously called the BIOS. Now often diminutively called by the name EFI. This is what initializes enough of the hardware so that the operating system can start. Additionally, it often provides facilities for the user to do basic configuration, and manage boot options.

In the ARM with SBCs landscape, U-Boot is the de facto solution for the Initial Boot Firmware. Though U-Boot is confusingly, but rightly, often referred to as a Boot Loader. U-Boot plays double duties often. It is tasked with initializing the hardware, and often also used to handle loading and booting the operating system.