If you're using Ubuntu 12.10 with Unity or some other desktop environment and want to switch to a complete GNOME 3 desktop experience without installing Ubuntu GNOME Remix 12.10, you can do this by simply installing a few packages.
Using the instructions below, you won't just install GNOME Shell, but also the default settings and applications that come with Ubuntu GNOME Remix. There are also some optional steps to install the GNOME 3 applications which are missing from Ubuntu GNOME Remix.
sudo apt-get install full-gnome3-experience
No, the command in the header won't work, but you'll get a complete GNOME 3 experience in Ubuntu 12.10 by following the steps below.
1. Install the Ubuntu GNOME packages
You can simply install the "gnome-shell" package if GNOME Shell is all you want, but if you want the whole GNOME 3 desktop which includes the default applications as well as the default settings, use the command below:
When prompted, select GDM as the default display manager.
sudo apt-get install ubuntu-gnome-desktop ubuntu-gnome-default-settings
If you already had GDM installed and the package manager didn't prompt you to choose between LightDM and GDM or you've selected LightDM by mistake, you can run the following command:
sudo dpkg-reconfigure gdm
And select GDM instead of LightDM (more about changing the display manager, here). You can use LightDM with GNOME Shell, but you won't get the complete GNOME 3 experience - for instance, GNOME Shell won't use the new GNOME 3.6 lock screen.
It is also a good idea to remove the "ubuntu-settings" package:
sudo apt-get remove ubuntu-settings
Note that removing this package, the "ubuntu-desktop" package will be removed as well. This is just a meta package and your system shouldn't be affected by it.
The "ubuntu-settings" package is used to set various Ubuntu defaults, like the window button order, which Rhythmbox plugins are enabled by default and so on.
2. Install missing GNOME 3 packages
Even though they are part of the default GNOME 3 application stack, GNOME Documents and Boxes are not installed by default with the ubuntu-gnome-desktop package. Install them using the following command:
Note: Boxes is only available on 64bit due to a bug!
sudo apt-get install gnome-documents gnome-boxes
3. Upgrade GNOME Control Center, Nautilus, Totem and other GNOME 3 packages to version 3.6.x
Some packages in the Ubuntu 12.10 repositories aren't updated to the latest 3.6.x version. So, like we wrote a while back, you can use the GNOME3 PPA to upgrade these applications.
Add the PPA using the following command:
sudo add-apt-repository ppa:gnome3-team/gnome3
Then, launch Software Updater from Dash / menu and use it to upgrade your packages.
The packages that will be upgraded once you add the PPA are: GNOME Control Center 3.6.3, Aisleriot 3.6.0, Brasero 3.6.0, Nautilus 3.6.3 and Totem 3.6.2. The PPA also provides Transmission 0.7.1, Transmageddon 0.23 and Sound Juicer 3.5.0.
4. Remove overlay scrollbars
One thing I've noticed after following the steps above myself, is that GNOME Shell continues to use Ubuntu's overlay scrollbars. If you want to use the GNOME 3 scrollbars instead, remove overlay scrollbars using the following command:
sudo apt-get remove overlay-scrollbar*
Once you're done, restart your computer (a logout may be enough for most stuff, but to get all the changes, including GDM for the login screen, a restart is probably a better idea) and select "GNOME" from the login screen.
some info via Ubuntu GNOME Remix 12.10 release notes