# Leaves a tag file indicating this reason; if the tag file exists
    # and disk space is above the threshold + 10GB, the queue/evaluator will be
    # restarted; starting it if it is already started is not harmful.

            if [ $(($(stat -f -c '%a' /nix/store) * $(stat -f -c '%S' /nix/store))) -lt $((${toString cfg.minimumDiskFree} * 1024**3)) ]; then
                echo "stopping Hydra queue runner due to lack of free space..."
                systemctl 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
                echo "stopping Hydra evaluator due to lack of free space..."
                systemctl stop hydra-evaluator
            fi

            spaceleft=$(($(stat -f -c '%a' /nix/store) * $(stat -f -c '%S' /nix/store)))
            spacestopstart() {
              service=$1
              minFreeGB=$2
              if [ $spaceleft -lt $(($minFreeGB * 1024**3)) ]; then
                if [ $(systemctl is-active $service) == active ]; then
                  echo "stopping $service due to lack of free space..."
                  systemctl stop $service
                  date > /var/lib/hydra/.$service-stopped-minspace
                fi
              else
                if [ $spaceleft -gt $(( ($minFreeGB + 10) * 1024**3)) -a \
                     -r /var/lib/hydra/.$service-stopped-minspace ] ; then
                  rm /var/lib/hydra/.$service-stopped-minspace
                  echo "restarting $service due to newly available free space..."
                  systemctl start $service
                fi
              fi
            }
            spacestopstart hydra-queue-runner ${toString cfg.minimumDiskFree}
            spacestopstart hydra-evaluator ${toString cfg.minimumDiskFreeEvaluator}