os/doc/start/iso.md

ISO

Making and writing an installable iso for hosts/NixOS.nix is as simple as:

flk iso NixOS

dd bs=4M if=result/iso/*.iso of=/dev/$your_installation_device \
  status=progress oflag=sync

This works for any file matching hosts/*.nix excluding default.nix.

ISO image nix store & cache

The iso image holds the store to the live environment and also acts as a binary cache to the installer. To considerably speed up things, the image already includes all flake inputs as well as the devshell closures.

While you could provision any machine with a single stick, a custom-made iso for the host you want to install DevOS to, maximises those local cache hits.

For hosts that don't differ too much, a single usb stick might be ok, whereas when there are bigger differences, a custom-made usb stick will be considerably faster.