ansible Make sure this host can be reached over ssh

搭建好ansible后，在/etc/ansible/hosts 文件中添加如下：
[all]
192.168.220.141 ansible_ssh_user=root ansible_ssh_port=22 ansible_ssh_pass=root

然后在机器上执行：
[root@localhost ansible]#  ansible all -m ping
192.168.220.141 | UNREACHABLE! => {
    "changed": false, 
    "msg": "SSH Error: data could not be sent to the remote host. Make sure this host can be reached over ssh", 
    "unreachable": true
}
好奇怪啊， 以前搞的时候挺顺利的！
不得已只好
[root@localhost ansible]#  ansible all -m ping -vvvv 
......
......
......

问题原因：
Since you are not using SSH keys to authenticate, you must try running "export ANSIBLE_SCP_IF_SSH=y" before running ansible-playbook with -vvv option. 

最后找到解决方法：
[root@localhost ansible]#  export ANSIBLE_SCP_IF_SSH=y  ##执行这个命令即可正常！
[root@localhost ansible]#  ansible all -m ping
192.168.220.141 | SUCCESS => {
    "changed": false, 
    "ping": "pong"
}