php实现定时创建指定大小文件脚本

    <?php  
        $timestamp = time();  
        $id = uniqid();  
        $filename = "/tmp/{$timestamp}.img";  
        $cmd = "dd if=/dev/zero of=$filename bs=4m count=5; echo $id >> {$filename}";  
        exec($cmd, $ret, $output);  
    ?>