Enable Root Login over SSH

1. As root, edit the sshd_config file in /etc/ssh/sshd_config:

nano /etc/ssh/sshd_config

2) Add a line in the Authentication section of the file that says PermitRootLogin yes. This line may already exist and be commented out with a "#". In this case, remove the "#".

# Authentication:

#LoginGraceTime 2m

PermitRootLogin yes

#StrictModes yes

#MaxAuthTries 6

#MaxSessions 10

3) Save the updated /etc/ssh/sshd_config file.

4) Restart the SSH server:

service sshd restart

source: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/v2v_guide/preparation_before_the_p2v_migration-enable_root_login_over_ssh

Common Issues:

If the root have locked by too many wrong authentications. Try:

usermod -U root