title: 'su' command in Docker returns 'must be run from terminal'
body: <p>I'm developing a docker environment for teaching purposes and need to be able to switch users inside docker.</p>
  
  <p>I set up the 'user' user with a password but when I try to switch to it with su, I get "su must be run from terminal".</p>
  
  <p>I get this if I try to ssh into the docker and also by issuing commands through a php shell (an apache service is running on the Docker instance).</p>
  
  <p>Any help is much appreciated.</p>