[ Thanks to Jane Walker for this link.
]
“Many security controls are ineffective or can be overridden if
an attacker gets physical access to your hosts, especially if
attackers are able to reboot those hosts. For example, by rebooting
your Red Hat Enterprise Linux server, an attacker can sign into
single user mode and change your root password–achieving a total
compromise of your server.“In this tip, I will look at how you can secure your GRUB boot
loader with a password that will prevent unauthorized access to
your hosts after a reboot…”