Ubuntu's default root password is random, that is, each boot has a new root password.
Acquisition method:
1. Enter the command sudo passwd, (or sudo passwd root)
2. Enter the current user password
3. The terminal will prompt us to enter a new password
4. In the confirmation time
After the amendment is successful, enter the command su root, then enter the new password on it.
Reproduced in: https: //www.cnblogs.com/liuming8080/p/3810694.html