Users and groups

Adding an existing user to an existing group 
 usermod -a -G theExampleGroup theExampleUser 
 Changing the primary group of an existing user 
 usermod -g theExampleGroup theExampleUser 
 See wich groups the user belongs to 
 groups theExampleUser 
 Add an existing user to the sudo group 
 usermod -aG sudo username 
   Add a new user with name, shell and home directory 
 sudo useradd -m -c "Samwise the Brave" sam -s /bin/bash 
   
 https://www.cyberciti.biz/faq/howto-linux-add-user-to-group/ 
 https://www.digitalocean.com/community/tutorials/how-to-create-a-sudo-user-on-ubuntu-quickstart 
 https://askubuntu.com/questions/643411/ubuntu-14-04-new-user-created-from-command-line-has-missing-features