Unity Supported? No

Having run the update overnight (yes, overnight) on the Dell laptop to get onto Ubuntu Natty 11.04, I do believe that Ubuntu has hit it's 'Vista moment' in terms of compatibility. Remember when Windows Vista hit a massive road-block in the number of hardware devices that were no longer supported? 11.04 is at that point with graphics.

At log-on, the X-server informs me that I don't have the hardware required to run the Unity interface...

This is, of course, the never-ending problem of Ubuntu Linux never getting on top of compatibility issues with nVidia and ATI graphics cards. The variety of cards and lack of standards between them is well known by now, yet Canonical is pushing ahead with Unity 3-D graphics regardless.

I keep finding repeated questions as to why a desktop needs such a complex 3-D environment, on machines that can quite happily run 3-D games. Including mine...

You can run the test in Ubuntu 11.04 by running the command:

sudo /usr/lib/nux/unity_support_test -p

On the Dell 6400 I get:

OpenGL vendor string:   NVIDIA Corporation
OpenGL renderer string: GeForce Go 7300/PCI/SSE2
OpenGL version string:  2.1.2 NVIDIA 270.41.06

Not software rendered:    yes
Not blacklisted:          no
GLX fbconfig:             yes
GLX texture from pixmap:  yes
GL npot or rect textures: yes
GL vertex program:        yes
GL fragment program:      yes
GL vertex buffer object:  yes
GL framebuffer object:    yes
GL version is 1.4+:       yes

Unity supported:          no

The 'not blacklisted = no' doesn't mean it works.
The reply from Canonical:
"We blacklisted Geforce Go 7300/7400 because of some freezes at startup with the "nvidia-current" driver.
It seems that unity 3D can run with the "nvidia 173" driver with those card. However, you will get some slowness, you are warned!"

I switched to the nVidia 173 driver (I was running the 'recommended' current version, which is evidently not current enough). To workaround the 3-D detection at startup, you can edit your environment file:

sudo gedit /etc/environment

Add: UNITY_FORCE_START=1 to the end of the file.

Save the file and reboot

Choose the "ubuntu" session in the gdm login (the default session choice). This bypasses the detection and try to start unity 3D.

Alternatively you can install unity_2d from the repo's in 11.04, to get the lower-res and less-glossy flat version of Unity. Why you would want to is the subject of an entirely different discussion... RC