nix-collect-garbage determine the set of unreachable store paths nix-collect-garbage --invert --no-successors The command nix-collect-garbage determines the paths in the Nix store that are garbage, that is, not reachable from outside of the store. These paths can be safely deleted without affecting the integrity of the system. --invert Causes the set of reachable paths to be printed, rather than the unreachable paths. These are the paths that may not be deleted. --no-successors Causes nix-collect-garbage not to follow successor relations. By default, if a derivation store expression is reachable, its successor (i.e., a closure store expression) is also considered to be reachable. This option is always safe, but garbage collecting successors may cause undesirable rebuilds later on. To delete all unreachable paths, do the following: $ nix-collect-garbage | xargs nix-store --delete