If you got an RSA private key file and need use it to login SSH server on Mac os system, you can direct use the follow command, it's working for Mac's Terminal too. 

{ Login Command } 

ssh root@12.10.117.126 -p 2201 -i /usr/data/yiilib.comKeys/yiilib.com.pem

{ PS }

set the pem file read only for cur user only