Centos 7 : Reset root password

The steps:

1. During boot menu, press (e) to edit existing kernel

2. Scroll down and find the line with (ro). Change (ro) with rw init=/sysroot/bin/sh. Ctrl-x to start

3. In emergency mode. Type #chroot /sysroot

4. Change the root password. Type #passwd root

5. Update the SELinux. Type #touch / .autorelabel

6. Exit and Reboot