stage-1

$ nix-build -A stage-1
/nix/store/am4yghy0jn8p7apgsrqi5n4c0nv9lqy9-stage-1

stage-1 is a script defined as config.system.build.bootStage1. It is the content of the initrd.

TODO Describe stage-1.

It prepares the Nix store (at /mnt/nix/store, which will be at /nix/store once switch_root is performed).

The final action of stage-1 is to call switch_root (using /mnt as the new root) to execute stage-2.

In vpsadminos, the stage-1 exists as a script, stage-1-init.sh (just like stage-2-init.sh). It contains code testing a possible nolive flag, and thus the two branches of the if statement.

In not-os, the flag is defined at build time so the generated script contains only the desired code. Similarly, the overlay kernel module is loaded only if necessay. The resulting script is less flexible but I like the idea of generating exactly what we decide.