Simply put:

• If you open a shell or terminal (or switch to one), and it asks you to log in (Username? Password?) before it gives you a prompt, it's a login shell.


• If it doesn't (like gnome-terminal), and lets you use it straight away, it's a non-login shell.

If you are a normal user of Ubuntu Desktop, the only login shell is...your desktop (you type a password to get in, right ;)? Well, technically it's a login shell that starts a GUI, but that's getting in to jargon. And yes, it will read the settings in .profile

The only time you (a normal user) will probably see a login shell that looks like a login shell is if you are having some problem with your desktop and you switch to a virtual terminal with the Ctrl+Alt+F1 shortcut.

The other general cases for having a login shell include:

• accessing your computer remotely via ssh (or connecting locally with ssh localhost)


• simulating an initial login shell with bash -l (or sh -l)


• simulating an initial root login shell with sudo -i
  
  
  
  • or sudo -u username -i for another non-root user
  
  
  
  


• authenticating as another non-root user with su - username (and their password)


• using the sudo login command to switch user