Disable Root SSH Login on Linux

One of the biggest security holes you could open on your server is to
allow directly logging in as root through ssh, because any cracker can
attempt to brute force your root password and potentially get access to
your system if they can figure out your password.

It's much better to have a separate account that you regularly use and
simply sudo to root when necessary. Before we begin, you should make
sure that you have a regular user account and that you can su or sudo to
root from it.

To fix this problem, we'll need to edit the sshd_config file, which is
the main configuration file for the sshd service. The location will
sometimes be different, but it's usually in /etc/ssh/. Open the file up
while logged on as root. 

vi /etc/ssh/sshd_config

Find this section in the file, containing the line with
"PermitRootLogin" in it.

#LoginGraceTime 2m
#PermitRootLogin no
#StrictModes yes
#MaxAuthTries 6

Make the line look like this to disable logging in through ssh as root.

PermitRootLogin no

Now you'll need to restart the sshd service:

/etc/init.d/sshd restart