If you want to try the latest Ubuntu 12.04 Precise Pangolin alpha or a daily build in VirtualBox (guest), you'll stumble upon a few issues like: VirtualBox can't boot from the 32bit ISO because PAE is not enabled by default so you'll get a kernel error, the mouse or the Internet connection isn't working or the screen is glitchy and black in Unity 3D after installing the VirtualBox Guest Additions from the repositories (required if you want to use Unity 3D).
So here is how to fix these issues and run the latest Ubuntu 12.04 Precise Pangolin build with Unity 3D in VirtualBox.
Before proceeding, make sure you've installed the latest VirtualBox 4.1.x (4.1.8 at the time I'm writing this post).
Can't boot - PAE not enabled by default on 32bit
When you firstly want to boot the latest Ubuntu 12.04 Precise Pangolin 32bit ISO, you'll get a message similar to this: "This kernel requires the following features not present on the CPU: pae. Unable to boot - please use a kernel appropriate for your CPU".
This occurs because Ubuntu 12.04 uses the PAE kernel by default for 32bit. To fix it, all you have to do is select the virtual machine, then click "Settings" and under System > Processor, check the "Enable PAE/NX" box:
Now you should be able to boot the live CD.
Mouse not working
The second issue: the mouse isn't working by default. Here's a work-around (which we've also posted in our Ubuntu 12.04 Alpha 2 post): start the machine and from the menu, select Machine > Disable Mouse Integration:
Later on, if you install the VirtualBox guest additions, there's no need for this work-around and the mouse should work without other tweaks.
Internet not working
If your VirtualBox Ubuntu 12.04 guest can't connect to the Internet, select Devices > Network Adapters and under "Attached to", select "Bridge Adapter". You guest machine Internet connection show now disconnect and reconnect and it should then work.
Fix Unity 3D (with Compiz) display issues
If you've installed VirtualBox Guest Additions from the repositories (by installing the virtualbox-guest-utils package), and you're running the latest updates on your Precise machine, you've probably encountered some annoying display issues: invisible / black boxes, screen doesn't gets refreshed properly (Dash still shows up after being closed), etc:
These issues are caused by the latest VirtualBox Guest Additions from the Precise repositories. Until this is fixed, you can install the VirtualBox Guest additions manually.
Firstly, make sure you've removed VirtualBox Guest Additions installed from the Ubuntu Precise repositories:
sudo apt-get remove virtualbox-*
And install VirtualBox Guest Additions from the menu, via Devices > Install Guest Additions:
Now reboot the machine and Ubuntu 12.04 Precise Pangolin with Unity 3D should work.