Clients

This kernel requires following features not present on the CPU: pae

Issue

Trying to run Linux based OS on Oracle VM VirtualBox. Following error is displayed:

List and run last used commands in Linux

To list through most recently used commands one by one use Arrow-Up key

To display all used commands:
history

To run a command from the history list:
!391
where 391 command number

Ubuntu Grub - Change Default OS

If you install Ubuntu as a second Operating System alongside Windows, every time computer boots you will be presented with a Grub boot menu where you can make a choose which OS to boot. If you don't make any choice in 10 seconds your default OS will boot. Obviously after installing Ubuntu it will become the default Operating System.
You may want to change your default OS or reduce Grub timeout. Probably easiest way to achieve this is to install StartUp-Manager.

Open Terminal and run sudo apt-get install startupmanager and wait until installation is completed.
Open Dash Home, type "Startup" in the search box and open StartUp-Manager
In StartUp-Manager select your Default OS and reduce reduce timeout if required. Click Close to save changes

Disable Ubuntu Unity Launcher Autohide

Unity 3D on Ubuntu 11.04 (Natty Narwhal) and Ubuntu 11.10 (Oneiric Ocelot)

Use this method to disable Unity Launcher autohide on Ubuntu 11.04. On Ubuntu 11.10 this will only work if you use Unity 3D. For Unity 2D check the second method below. Unity 2D was introduced in Ubuntu 11.10 to provide Unity interface for computers without accelerated 3D graphics. You can read more about differences here.

1. Install CompizConfig Settings Manager: Open Terminal and run: sudo apt-get install compizconfig-settings-manage

2. Open Dash Home, type "compiz" in the search box and open CompizConfig Settings Manager

3. Open Ubuntu Unity Plugin
Disable Ubuntu Unity Launcher Autohide

4. In Hide Launcher select Never.

This will affect only logged on user.

Unity 2D on Ubuntu 11.10 (Oneiric Ocelot)

1. Install dconf-tool tool: Open Terminal and run: sudo apt-get install dconf-tools
Disable Ubuntu Unity Launcher Autohide

2. To disable Unity Launcher auto hide, run: dconf write /com/canonical/unity-2d/launcher/use-strut true

3. To re-enable Unity Launcher auto hide, run: dconf write /com/canonical/unity-2d/launcher/use-strut false