Ideas: into single-user mode and change the root password is not required because the single-user mode root password to login
After entering 
↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ press the Enter ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ Press e ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ cursor to highlight the second line and then enter the e ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
↓ ↓ ↓ ↓ ↓ ↓↓ ↓ ↓ ↓ ↓ ↓ later add a space to write a 1 ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
This step is to enter into single-user mode (linux run levels)
↓ ↓ ↓ ↓ ↓↓ ↓ ↓ ↓ ↓ ↓ ↓↓ ↓ Enter ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
↓ ↓ ↓ ↓ ↓↓ ↓ ↓ ↓ ↓ ↓ ↓↓ ↓ input b ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
And then it will go directly to single-user mode
You can change the root password
passwd root
