$sudo passwd root
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
$su
Password:
root@username-laptop:/home/username/Downloads/Python-2.7#
$sudo passwd root
Enter new UNIX password:
Retype new UNIX password:
passwd: password updated successfully
$su
Password:
root@username-laptop:/home/username/Downloads/Python-2.7#
转载于:https://www.cnblogs.com/stillzhl/archive/2011/08/20/ubuntu_root.html