How to make guest sessions start with Unity 2D by Default?

Question

My PC does not have enough resources to run two accounts in Unity 3D.

When I open a guest account from an already started session, it uses Unity 3D by default. How do I change that?

Answer 1

It is an interesting question. I've had a look at this, and it seems to be a bug somewhere. In my opinion, you should've been able to add a file called .dmrc to /etc/guest-session/skel containing

[Desktop]
Session=sessionname

Where sessionname can be something like "ubuntu", "ubuntu-2d", "gnome", etc. But this doesn't work no matter what I've tried. There are several bug reports about similar issues, so this will be looked into.

I did come up with a solution for you, however, but it's really hacky and just hides the problem without fixing it. But it does work. Open a terminal and paste the following commands: (Make sure you get the whole commands, otherwise you'll get into trouble)

sudo mv /usr/share/gnome-session/sessions/ubuntu.session /usr/share/gnome-session/sessions/ubuntu-3d.session
sudo mv /usr/share/gnome-session/sessions/ubuntu-2d.session /usr/share/gnome-session/sessions/ubuntu.session

This just swaps the two sessions, so any user who has chosen to use Unity and not Unity 2D will also be logged in with Unity 2D until he/she chooses differently again. This also means that any new users you create will default to using Unity 2D.