public function moveOldBackup()
    {
        Service::$log->msg('Filesystem: moving old backups');
        // remove the 2-day file
        if(file_exists($this->storagePath.'backup-2days-old')){
            unlink($this->storagePath.'backup-2days-old');
        }

        // copy current 1-day file to 2-day
        $sourceFile = $this->storagePath . 'backup-1day-old';
        $destinationFile = $this->storagePath . 'backup-2days-old';
        if (file_exists($sourceFile)) {
            copy($sourceFile, $destinationFile);
        }

        // remove the old 1-day file
        $destinationFileTemp = $this->storagePath. 'backup-1day-old';
        if (file_exists($destinationFileTemp)) {
            unlink($destinationFileTemp);
        }

        Service::$log->msg('Filesystem: moving old backups done');

        return $destinationFile;
    }