@Override
  public void setStartLocator(String value) {
    startLocatorPort = 0;
    if (value == null) {
      value = DEFAULT_START_LOCATOR;
    } else {
      // bug 37938 - allow just a port
      boolean alldigits = true;
      for (int i = 0; i < value.length(); i++) {
        char c = value.charAt(i);
        if (!Character.isDigit(c)) {
          alldigits = false;
          break;
        }
      }
      if (value.length() > 0 && alldigits) {
        try {
          int port = Integer.parseInt(value);
          if (port < 0 || port > 65535) {
            throw new GemFireConfigException("Illegal port specified for start-locator");
          }
          startLocatorPort = port;
        } catch (NumberFormatException e) {
          throw new GemFireConfigException("Illegal port specified for start-locator", e);
        }
      }
    }
    startLocator = value;
  }
the locator startup code must be able to modify the locator log file in order to establish a
default log file if one hasn't been specified by the user. This method will change the log
file, but only in the configuration settings - it won't affect a running distributed system's
log file
geode-core/src/main/java/org/apache/geode/distributed/internal/DistributionConfigImpl.java