Cause of ssh password-free Logon (Public Key logon) Failure

The cause of ssh password-free login (Public Key login) failure a few days ago, the MyBookLive has become a brick-and-mortar. I removed the hard disk and re-built the system. Today, when I Configure ssh Login, www.2cto.com because the previous private key is still on the PC, directly copy the public key and put it in. ssh/authorized_keys, but found that the public key login is not good. it is very strange that previously, except for a centos6 configuration failure (that is because of selinux, centos6 bug, you can use restorecon-R-v/root /. and MBL is based on debian. view sshd. log suddenly realized that it was a touch before creating the authorized_key. I did not pay attention to the permission of 666, but I did not recognize the permission of sshd... chmod 600. ssh/authorized_keys can be used or 644.