docs: function write(conf) {
    var contents = process.pid + EOL
      , file = conf.get(ConfigKey.PIDFILE);
    // can be the empty string
    if(file) {
      try {
        fs.writeFileSync(file, contents);
        log.notice('wrote pid %s to %s', process.pid, file);
      }catch(e) {
        log.warning('failed to write pid file (%s): %s', file, e.message);
      }
    }
  }