[CentOS] SSH authorization file fail and solution.

I encountered a situation where after I've set up the rsa key on my server (.ssh/authorized_keys), the server still keep asking for password.

So I did a little search on Google and here is a perfect answer:
http://askubuntu.com/questions/110814/server-keeps-asking-for-password-after-ive-copied-my-ssh-public-key-to-authoriz

Solution:

1. look at /var/log/secure (CentOS) for detail log and reasons.
2. change .ssh/authorized_keys's permission to 600 (owner read/write only)