Reset the password after you forget the root password.

1. When the grub screen appears, use the up and down keys to select the one you usually start Linux (do not select DoS), and then press the e key
2. Use the up and down keys again to select the one you usually start Linux (similar to kernel/boot/vmlinuz-2.4.18-14 Ro root = label =/), and then press the e key
3. Modify the command line you see and add single. The result is as follows:
Kernel/boot/vmlinuz-2.4.18-14 single Ro root = label =/
4. Press enter to return, and then press the B key to start, you can directly enter the Linux Command Line
5. Enter passwd root and press Enter.
6. Change the new password
7. Log On with the new password after reboot.