Adding a new user to a Ubuntu/Debian server

Execute this on shell.sh

# Let' add Mario to the server

# Add the user with the interactive shell
adduser mario 

# Check the creation of the user home directory
ls -al /home/mario/

# and set the default console to bash
chsh -s `which bash` mario

# Add the ssh key for mario here:
mkdir /home/mario/.ssh/
nano /home/mario/.ssh/authorized_keys

# Add the user to the users allowed to use ssh 
nano  /etc/ssh/sshd_config
# and edit/add the line
AllowUsers root mario luigi yoshi

# restart the ssh agent
/etc/init.d/ssh restart

# optional: add the user to the sudoers
sudo usermod -aG sudo mario

# bonus: you can change the user password with
passwd mario