How can I identify a fault during logon?

How can I solve the logon authentication fault-general Linux technology-Linux technology and application information? The following is a detailed description. On July 6, last June, I installed Debian6.0.3 on the virtual machine. Later, I did not continue using it. When I log on a few days ago, I enter my password and prompt "identify a fault ". I tried several common passwords. I may have forgotten my password. Follow the methods found on the Internet to change the password.
When entering the system interface, there is a row at the bottom of the default wait for five seconds, press the E key. Enter the editing mode. There are only two rows. Use the arrow keys to select 'debian GNU/Linux,... (recovery mode) 'and press e to enter the editing mode. However, the line starting with "kernel" cannot be found on the Internet. You have to change the last line of "ro single" to "rw single init =/bin/bash ". Press the "B" button introduced on the Internet to enter B. After several attempts, the following Operation prompt is displayed. Press Ctrl + X to restart.
Enter
Root @ (none) # mount-a press enter and enter
Root @ (none) # passwd root press enter, press the prompt to enter the new password press enter, then enter a check, and press Enter. The system prompts that the password is successfully updated. Input
Root @ (none) # reboot
When I log on with a common user and a new password, the system prompts "identify a fault ". To log on with the root account and the new password, the system prompts "identify a fault ". You cannot access the system. I tried to change the password of the "root" account. Didn't I change the password of a common user? I am still a netizen who affirmed this. Enter the single user mode again.
Root @ (none) # mount-
Root @ (none) # passwd username (change the password of a common user and replace usrename with the actual user name)
After restart, enter the logon page and enter the new password.
I just learned Debian, and this simple problem has plagued me for two days. I am very smiling. I just want to avoid detours like I do for beginners.