code: public final void begin() {
      this.file = this.getAppender().getIoFile();
      if (this.file == null) {
        this.getAppender().getErrorHandler()
            .error("Scavenger not started: missing log file name");
        return;
      }
      if (this.getProperties().getScavengeInterval() > -1) {
        final Thread thread = new Thread(this, "Log4J File Scavenger");
        thread.setDaemon(true);
        thread.start();
        this.threadRef = thread;
      }
    }
docs: Starts the scavenger.