NixOS BTW: NixOS, Nix, and Flakes Administration

Administer NixOS without falling back into imperative distro muscle memory. NixOS is declarative, functional, and atomic: the system is a value computed from a configuration, every change becomes a new immutable generation in /nix/store, and rollbacks are a bootloader entry away. This skill keeps that model intact, then layers in the practical stack: channels vs flakes, nixos-rebuild vs nix CLI, home-manager, nix-darwin, store hygiene, overlays, module writing, secrets, and the Determinate Nix and Lix lanes.

The places NixOS breaks are NixOS-shaped: channel drift, flake input staleness, garbage collection that nukes a needed derivation, overlays fighting, nix-env -i poisoning the user profile, hardware modules missing, or people treating /etc/nixos/configuration.nix like a normal Linux config file.

Why people run it. Atomic upgrades and rollbacks, bit-for-bit reproducible systems, disposable dev shells, fleet-wide configuration without a separate config-management tool, and a single language for a workstation, a server, a container image, a NixOS VM, and a macOS laptop via nix-darwin.