If you have forgotten the root password on Linux CentOS you need a data manipulation:
1) when loading the GRUB loader to stop by pressing any key.
2 Select the desired stitch and) push (e).
3) select the line with the kernel (kernel/vmlinuz/… of …kernel version.../root = LABEL =/)
4) Appends to the end of the line is single and press Enter
5) Press b to boot the system
6) after changing password (passwd)