User

• Add user

  # do all the defaults: create home, select shell, prompt for password.
  adduser hawkey
  
  # do nothing
  useradd hawkey
  useradd -d /home/hawkey -s /bin/bash 
  
  passwd hawkey # change password
  bash

• Delete user

  userdel hawkey
  userdel -r hawkey # delete home
  bash

• switch user

  su hawkey
  su # root
  bash

• add user to group

  usermod -aG g
  bash

• add sudoer

  # recommend use this!
  usermod -aG sudo hawkey
  bash

  Or

  visudo # however, this is nano
  vim /etc/sudoers
  bash

  and append a line:

  hawkey ALL=(ALL) NOPASSWD:ALL

• Change shell

  chsh -s /bin/bash # but never change shell for root !!!
  bash

  Or

  vi /etc/passwd
  bash

  and modify the corresponding line.