What about forgetting the password of the Linux root user?

Before forgetting the Windows password, either use the tool to clear it or reload the system. What if you forget the root password of the Linux system? Do you use tools like windows to crack or reload the system? Haha, not all. This method is very simple, now do it again, one to do the study notes, and then share to everyone, I hope that will not be able to help the birds, see the following steps (here is the CentOS 6.4 example):

1, in the 3 seconds of power-on press the ENTER key, the following interface will appear:

2, according to the letter E, the following interface appears

3, again after the letter E, the following interface appears, and then add a single after quiet, or the number 1, or the letter S can be, here I add a single:

4, then press ENTER, followed by enter the letter B, the system started into a single user mode, and then enter the passwd command to modify the password:

What about forgetting the password of the Linux root user?