SSH password-free login (root) under Linux

Configure host A to log in to host A without a password, host B
eg:
A:192.168.113.181
B:192.168.113.182
Perform the following on host A:
　1.　

$ssh-keygen -t rsa -P ''

-------------------- Then keep pressing the Enter key, and the generated key will be saved in the .ssh/id_rsa file according to the default option
　2.　

ssh-copy-id -i id_rsa.pub [email protected]

Just two simple steps, you can achieve it!
  Test it:

  [root@localhost .ssh]# ssh 192.168.113.182
  Last login: Tue Jan  5 14:48:10 2016 from 192.168.113.181