nixos/modules/system/boot/shutdown.nix

   1 { config, lib, pkgs, ... }:
   2
   3 with lib;
   4
   5 {
   6
   7   # This unit saves the value of the system clock to the hardware
   8   # clock on shutdown.
   9   systemd.services.save-hwclock =
  10     { description = "Save Hardware Clock";
  11
  12       wantedBy = [ "shutdown.target" ];
  13
  14       unitConfig = {
  15         DefaultDependencies = false;
  16         ConditionPathExists = "/dev/rtc";
  17       };
  18
  19       serviceConfig = {
  20         Type = "oneshot";
  21         ExecStart = "${pkgs.util-linux}/sbin/hwclock --systohc ${if config.time.hardwareClockInLocalTime then "--localtime" else "--utc"}";
  22       };
  23     };
  24
  25   boot.kernel.sysctl."kernel.poweroff_cmd" = "${config.systemd.package}/sbin/poweroff";
  26
  27 }