su not working in Debian 9?

Question

Debian

Hello.
Downloaded Debian 9. Installation went smoothly. Root password set.
The first boot of the system, everything is ok. I try to put the necessary programs.
~$ su
Password: toor
su authentication failure
The fact that I enter the password correctly is 100% Googled that you need to activate the root account.
But I can't do anything! Any command to edit or install requires root privileges.
This is some kind of nonsense!
Debian 8 - everything works as usual here. What the hell is in the new version?

Answer 1

Very strange.
I installed it again, only this time I did not specify the password for root during installation.
Now everything works.

Answer 2

Use sudo