code: public static Double getDiskUsage() {
          if (!OSInfo.isLinux() && !OSInfo.isMac()) {
              return 0.0;
          }
          try {
              String output = SystemOperation.exec("df -h " + duHome);
              if (output != null) {
                  String[] lines = output.split("[\\r\\n]+");
                  if (lines.length >= 2) {
                      String[] parts = lines[1].split("\\s+");
                      if (parts.length >= 5) {
                          String pct = parts[4];
                          if (pct.endsWith("%")) {
                              return Integer.valueOf(pct.substring(0, pct.length() - 1)) / 100.0;
                          }
                      }
                  }
              }
          } catch (Exception e) {
              LOG.warn("failed to get disk usage.");
          }
          return 0.0;
      }
docs: calculate the disk usage at current filesystem
  
  @return disk usage, from 0.0 ~ 1.0