Question: how to change forgotten root password in centos?
Answer: Step 1: Access Boot Menu. Restart the system, then tap the Esc key about once per second to launch the GRUB menu.
Step 2: Edit Boot Options. Use the arrows to highlight the version of Linux you boot into, then press e. ... 
Step 3: Remount the Drive. ... 
Step 4: Changing the Password. ... 
Step 5: Restart.