Using pkgs.lib on the spine of module evaluation is problematic
because the pkgs argument depends on the result of module
evaluation. To prevent an infinite recursion, pkgs and some of the
modules are evaluated twice, which is inefficient. Using ‘with lib’
prevents this problem.
The attribute ‘config.systemd.services.<service-name>.runner’
generates a script that runs the service outside of systemd. This is
useful for testing, and also allows NixOS services to be used outside
of NixOS. For instance, given a configuration file foo.nix:
{ config, pkgs, ... }:
{ services.postgresql.enable = true;
services.postgresql.package = pkgs.postgresql92;
services.postgresql.dataDir = "/tmp/postgres";
}
you can build and run PostgreSQL as follows:
$ nix-build -A config.systemd.services.postgresql.runner -I nixos-config=./foo.nix
$ ./result
This will run the service's ExecStartPre, ExecStart, ExecStartPost and
ExecStopPost commands in an appropriate environment. It doesn't work
well yet for "forking" services, since it can't track the main
process. It also doesn't work for services that assume they're always
executed by root.
