nix.gc.automatic = true;
    # $3 / $4 don't always work depending on length of device name
    nix.gc.options = ''--max-freed "$((200 * 1024**3 - 1024 * $(df /nix/store | tail -n 1 | awk '{ print $3 }')))"'';
    

    # We have our own crontab entries for GC, see below.
    nix.gc.automatic = false;

	    let
	      # If there is less than ... GiB of free disk space, stop the queue
	      # to prevent builds from failing or aborting.
	      checkSpace = pkgs.writeScript "hydra-check-space"
	        ''
	          #! /bin/sh
	          if [ $(($(stat -f -c '%a' /nix/store) * $(stat -f -c '%S' /nix/store))) -lt $((${toString cfg.minimumDiskFree} * 1024**3)) ]; then
                stop hydra_queue_runner
	          fi
              if [ $(($(stat -f -c '%a' /nix/store) * $(stat -f -c '%S' /nix/store))) -lt $((${toString cfg.minimumDiskFreeEvaluator} * 1024**3)) ]; then
                stop hydra_evaluator
              fi
	        '';
          compressLogs = pkgs.writeScript "compress-logs" ''
              #! /bin/sh -e
             touch -d 'last month' r
             find /nix/var/log/nix/drvs -type f -a ! -newer r -name '*.drv' | xargs bzip2 -v
           '';
	    in
	    [ "*/5 * * * * root  ${checkSpace} &> ${cfg.baseDir}/data/checkspace.log" 
	      "15 5 * * * root  ${compressLogs} &> ${cfg.baseDir}/data/compress.log"
              "15 02 * * * ${cfg.user} ${env} ${cfg.hydra}/bin/hydra-update-gc-roots &> ${cfg.baseDir}/data/gc-roots.log"
	    ];

      let
        # If there is less than ... GiB of free disk space, stop the queue
        # to prevent builds from failing or aborting.
        checkSpace = pkgs.writeScript "hydra-check-space"
          ''
            #! /bin/sh
            if [ $(($(stat -f -c '%a' /nix/store) * $(stat -f -c '%S' /nix/store))) -lt $((${toString cfg.minimumDiskFree} * 1024**3)) ]; then
          stop hydra_queue_runner
            fi
        if [ $(($(stat -f -c '%a' /nix/store) * $(stat -f -c '%S' /nix/store))) -lt $((${toString cfg.minimumDiskFreeEvaluator} * 1024**3)) ]; then
          stop hydra_evaluator
        fi
          '';

  };  
}

        collect = pkgs.writeScript "collect-some-garbage"
          # Arrange to always have at least 100 GiB free.
          '' #!/bin/sh -e
             available="$(df -B1 /nix/store | tail -n 1 | awk '{ print $4 }')"
             target="$((100 * 1024**3))"
             to_free="$(($available > $target ? 200 * 1024**2 : $target - $available))"
             echo "$available B available, and targeting $target B available"
             echo "thus, freeing $to_free B"
             exec "${pkgs.nix}/bin/nix-collect-garbage" --max-freed "$to_free"
          '';
        compressLogs = pkgs.writeScript "compress-logs" ''
            #! /bin/sh -e
           touch -d 'last month' r
           find /nix/var/log/nix/drvs -type f -a ! -newer r -name '*.drv' | xargs bzip2 -v
         '';
      in
        [ "15 03 * * * root  ${collect} &> ${cfg.baseDir}/data/gc.log"
          "15 13 * * * root  ${collect} &> ${cfg.baseDir}/data/gc.log"

          "*/5 * * * * root  ${checkSpace} &> ${cfg.baseDir}/data/checkspace.log"
          "15 5 * * * root  ${compressLogs} &> ${cfg.baseDir}/data/compress.log"
          "15 02 * * * ${cfg.user} ${env} ${cfg.hydra}/bin/hydra-update-gc-roots &> ${cfg.baseDir}/data/gc-roots.log"
        ];
  };
}