#1 Add user without password non-interactively
adduser --disabled-password --gecos "" username_new_user

#2 Grant root access to the user
usermod -aG sudo username_new_user

#3 Create a folder named .ssh
cd /home/username_new_user
mkdir ~/.ssh

#4 Create a blank file named id_rsa
cd ~/.ssh
touch id_rsa

#5 Change the file permission of id_rsa
sudo chmod 0444 id_rsa

#6 Change the ownership
sudo chown -R username_new_user: /home