To be able to log-in as NOT root and still be able to execute commands with root rights we need sudo. Users who should be able to use sudo must be part of the sudo-group. So we install sudo
sudo apt-get install sudo
and add the user to the group sudo with the following command:
sudo adduser <username> sudo
The reason behind it is, that it’s more secure to login as a „normal“ user and block root access altogether – or at least over ssh.