在php中限制已连接ftp的用户

我将每10秒运行一次cron作业，以连接和复制文件，然后删除。 我不会在cron复制文件等时运行cron，最好的方法是什么

我可以限制已连接的用户吗

try {
    $con = ftp_connect($server);
    if (false === $con) {
        throw new Exception('Unable to connect');
    }

    $loggedIn = ftp_login($con,  $username,  $password);
    if (true === $loggedIn) {
        echo 'Success!';
    } else {
        throw new Exception('Unable to log in');
    }

    print_r(ftp_nlist($con, "."));
    ftp_close($con);
} catch (Exception $e) {
    echo "Failure: " . $e->getMessage();
}

如果ftp软件本身允许您限制这一点，我不会感到惊讶。我可能想看看

if a certain file doesnt exist
    make the file
    do stuff
    delete file
else if the file exists, but its very old
    recreate the file
    do stuff
    delete file
else
    its busy