SSH login as root fails, but I'm sure I entered the right password

Question

What am I missing? I change the root password on a unix machine, then try to log in with that password. PasswordAuthentication is set to yes in sshd_config and the sshd daemon has been restarted. This behavior happens whether I log in remotely or locally:

root@ip-10-0-0-155:~# passwd
Enter new UNIX password: 
Retype new UNIX password: 
passwd: password updated successfully
root@ip-10-0-0-155:~# ssh root@127.0.0.1
root@127.0.0.1's password: 
Permission denied, please try again.
root@127.0.0.1's password:

Answer 1

Check this file: /etc/ssh/sshd_config and search for the line:

PermitRootLogin no

replace it by:

PermitRootLogin yes