How Linux modifies the root user's password

The root account of the Linux system is a very important account, but also the most privileged account, but sometimes forget the root password to do? Can not re-install the system, this is the next worst, in fact, Linux system, if you forget the root account password, you can enter the single user mode or other methods to modify the password. Of course, the specific way is related to boot Loader, OS, GRUB and Lilo are implemented differently. Boot Loader is a small program that runs before the operating system kernel runs. With this applet, we can initialize the hardware device and establish a mapping of the memory space to bring the system's hardware and software environment to a suitable state to prepare the correct environment for the final call to the operating system kernel. Here is a look at Red Hat Enterprise Linux 5 forgot the root password, how to modify the root account password: Forced to restart the Linux system, enter the interface shown below, you can press the up and down keys, select an option and then press "E" key.
Enter the following Grup interface

Select the second and then press the E key,
Press the left cursor, enter the next, and then add a single in front of the RO or root, press ENTER, and then press "B" key to start the Linux system into one-user mode

As shown below, when the boot is complete, enter passwd root to modify

After setting the new password, execute the restart command and reboot the system.

How Linux modifies the root user's password