Linux is a multi-user system, once people get to your root user, he can do whatever they like on your system, because the single-user on the system have full control permissions, if the improper operation or others to enter, then the consequences will be inconceivable, how to prevent the entry of single users, and has the following aspects of attention.
1, on the / etc / inittab file for protection, if the id: 3: initdefault in 3 to become one, you can boot directly into each single-user mode. On the / etc / inittab file to root, enter through the chown 700 / etc / inittab the property to other users can not modify on the line.
2, If you are using the lilo boot manner, possibly through linuxconf or directly modify lilo.conf to boot, waiting to enter the time when set to 0 or the shortest line. This case, if into single user mode, you can use floppy disks to boot.
3, if the use is conducted GRUB boot, the easiest way is to use GRUB password protection on startup option.
4, in order to prevent others from remotely destroyed the system restart, in addition to the ROOT password and / etc directory files for effective management but also should set the password on the CMOS, so that even if the system into single user mode, and can not directly start the computer to operate.