lyzh@ubuntu:~$ passwd root
passwd: You may not view or modify password information for root.
lyzh@ubuntu:~$ sudo passwd root
Enter new UNIX password: 
Retype new UNIX password: 
passwd: password updated successfully
lyzh@ubuntu:~$ 
lyzh@ubuntu:~$ 
lyzh@ubuntu:~$ su root
Password: 
root@ubuntu:/home/lyzh# 
root@ubuntu:/home/lyzh# 
root@ubuntu:/home/lyzh#