In Order to emergency, change configuration or reset root password. Follow following steps
1. Shutdown the computer 2. Boot into Recovery Mode --After BIOS load, hold down Shift key to access the grub menu --Once in grub menu, select the entry ending in "(recovery mode)" 3. From the next menu selected option to enter Root Session 4. At the root session, execute command mount -o remount,rw / to remount the filesystem as read-write
Then after you can reset the Root password to change the configuration.