PHP函数ssh2_connect不起作用

Following is my script:

下面是我的脚本:

    <?php
    $connection = ssh2_connect('XX.XX.XX.XX', 22);
    ssh2_auth_password($connection, 'root', '******');

    $stream = ssh2_exec($connection, 'useradd -d /home/users/test -m testftp');
    $stream = ssh2_exec($connection, 'passwd testftp');
    $stream = ssh2_exec($connection, 'password');
    $stream = ssh2_exec($connection, 'password');
    ?>
    <?php