A set of system “features” supported by this machine, e.g. kvm. Derivations can express a dependency on such features through the derivation attribute requiredSystemFeatures. For example, the attribute

requiredSystemFeatures = [ "kvm" ];

ensures that the derivation can only be built on a machine with the kvm feature.

This setting by default includes kvm if /dev/kvm is accessible, apple-virt if hardware virtualization is available on macOS, and the pseudo-features nixos-test, benchmark and big-parallel that are used in Nixpkgs to route builds to specific machines.