title: Grant/Revoke permissions on a service executing
body: <p>I'm using a service on which I'd like to write a script to be able to grant and revoke group on real time (while it's running). </p>
  
  <p>For now, I execute <code>usermod -aG group user</code> on the service before running it. It's working fine, but if I do the same command while it's already started, the user's mod isn't effective until I restart the service.</p>
  
  <p>Is there a way to do it properly ?</p>