The original Perl script is deprecated and is planned for removal in the 25.05 release. It will remain accessible until then by setting `system.switch.enableNg` to `false`.
- Built NixOS configurations now have a `$toplevel/bin/apply` script.
Unlike `switch-to-configuration`, it is capable of performing a complete `switch` operation.
If you call `switch-to-configuration` directly, you are recommended to use `apply` instead, and remove your call to `nix-env --profile /nix/var/nix/profiles/system --set $toplevel` or similar.
It will run the switch operation as a systemd unit if available, as `nixos-rebuild switch` would.
Benefits include:
- The `apply` script reduces the roundtrips required when performing a remote deployment with `nixos-rebuild switch --target-host HOST`.
- Developers and power users can now update NixOS in a single call.
- Alternative NixOS deployment methods have feature parity with `nixos-rebuild`, and NixOS can evolve all of its switching logic in one place.
- Support for mounting filesystems from block devices protected with [dm-verity](https://docs.kernel.org/admin-guide/device-mapper/verity.html)
was added through the `boot.initrd.systemd.dmVerity` option.
