rsync -Pav -e "ssh -i /home/pi/Documents/Qcloud.pem" ubuntu@a.jiazerui.com:/home/ubuntu/rescources /Downloads/Qcloud/
rsync -Pav -e "ssh -i /home/pi/Documents/Qcloud.pem" ubuntu@123.207.158.136:/home/ubuntu/rescources /home/pi/Downloads/Qcloud/
https://unix.stackexchange.com/questions/127352/specify-identity-file-id-rsa-with-rsynca
// http://blog.51cto.com/13444271/2112696
The end.