I'm trying to run Unity 2d in xubuntu, I installed the packages but when I try to run it I get
[FATAL] Settings schema 'com.canonical.Unity' is not installed
How can I get it to run? I'd like to install as little stuff as possible.
I think unfortunately you will have to install more dependencies, and the one you are missing is gnome-session, without which unity 2d can't run, and you get the error message you received. This is actually detailed at Launchpad; installing unity 2d manually from Synaptic does not automatically pull in the correct dependencies.
Running an apt-cache rdepends unity-2d proves this:
unity-2d
Reverse Depends:
unity-2d-dbg
unity-2d-common
libunity9
unity-2d-dbg
unity-2d-common
ubuntu-desktop
libunity9
gnome-session
|gnome-session
If you don't want absolutely everything that gnome-session includes, you could try installing it with the --no-install-recommends flag and this will install just the essential elements needed for unity-2d.
Run in terminal
sudo apt-get install gnome-session --no-install-recommends
It should not be necessary to install the ubuntu-desktop package as well, but keep that in mind if all else fails.
Using unity-2d should now be possible and it should be a login option at the Xubuntu screen and if you have any visual defects in it is also worth installing the following, according to this Launchpad report.
sudo apt-get install light-themes ubuntu-mono ubuntu-wallpapers-precise gnome-themes-standard
As the two bug reports at Launchpad have proven, you do need to install a fair amount of things to run unity-2d on Xubuntu.
