Installed a new version of ubuntu16.04, the root password has been wrong;
1. The default root password is random, that is, there is a new root password every time you boot. We can enter the command sudo passwd in the terminal, then enter the password of the current user, and then press the enter key
2. The terminal will prompt us to enter a new password and confirm it. The password at this time is the new root password. After the modification is successful, enter the command su root, and then enter the new password and it will be ok