When booting into single user mode you will not be prompted for the root password. This is something every attacker knows and prays on once he has gained physical access to you box. So what do you do?
Firstly, a good sys admin knows not to forget the root password. Login in as root is never a good idea so using sudo is always advised.
This still leaves the single user mode vulnerable, to secure it you will have to append the following line “su:S:wait:/sbin/sulogin” to your “/etc/inittab” file.
Now, every time you boot into single user mode you will be prompted for the root password.

# password protect single user mode
su:S:wait:/sbin/sulogin

PS: Always remember you password, if you can’t then write in down in a safe place.