So here is my two-minute recipe guide to getting the latest VirtualBox product installed (for zero dollars!) on Scientific Linux 6.1. (You could always just download the relevant rpm and install it directly, but I prefer to do all my package management via yum wherever possible, so that’s the approach described here).

1. Get the gpg key

VirtualBox is supplied as a bunch of rpm packages which have been digitally signed. By checking the signature, you know no-one’s messed about with the packages before they reached you. It therefore makes sense to obtain and install the digital key needed to do that signature check. It’s easy to do, as root, at a command prompt, by issuing these two commands:

wget http://download.virtualbox.org/virtualbox/debian/oracle_vbox.asc
rpm --import oracle_vbox.asc

2. Create the yum repository

Again as root, issue this command to create a new, blank repository file:

gedit /etc/yum.repos.d/virtualbox.repo

Now paste in these contents to the empty file:

[virtualbox]
name=RHEL/CentOS-$releasever / $basearch - VirtualBox
baseurl=http://download.virtualbox.org/virtualbox/rpm/rhel/6.0/$basearch
enabled=1
gpgcheck=1
gpgkey=http://download.virtualbox.org/virtualbox/debian/oracle_vbox.asc

Save the file changes and close down gedit. Just in passing, you might note that I’ve changed this file from the version which Oracle themselves makes available on the VirtualBox website. Specifically, their baseurl uses an environment variable, called $releasever, where I have hard-coded in the number 6.0. The trouble, of course, is that if you are using the latest versions of Scientific Linux or Centos, you’ll be picking up a releasever of 6.1 or 6.2 …and no such directory exists on the VirtualBox servers. You’d need to manually check out those server’s directory structure to see if that situation changes over time.

3. Install the Software

As root once more, the following one-liner will display all the different versions of VirtualBox that are available for installation:

yum search VirtualBox

You might see this sort of output in return:

Loaded plugins: refresh-packagekit
virtualbox | 951 B 00:00
virtualbox/primary | 4.4 kB 00:00
virtualbox 17/17
============== N/S Matched: VirtualBox ==============
VirtualBox-3.2.x86_64 : Oracle VM VirtualBox
VirtualBox-4.0.x86_64 : Oracle VM VirtualBox
VirtualBox-4.1.x86_64 : Oracle VM VirtualBox

This shows that Oracle keeps a couple of older versions of the software alive and available, should you need to use them. Most people, though, will really only need the latest version, so pick that from the list and issue an appropriate “yum install” command. In my case, given the above output, this command will do the right thing:

yum -y install VirtualBox-4.1.x86_64

It’s a 58MB download or so, and as it’s installed you might see this message appear:

Running Transaction
 Installing : VirtualBox-4.1-4.1.8_75467_rhel6-1.x86_64 1/1

Creating group 'vboxusers'. VM users must be member of that group!

This gives you the clue to the last stage of the installation process…

4. Assigning Group Privileges

The software installation has created a new O/S group, called vboxusers, but it won’t have made your user account a member of that group. That needs to be fixed.

From the Gnome top panel, clieck System > Administration > Users and Groups. Find your user details on the Users tab and double-click the entry. Switch to the Groups tab, scroll down and check the vboxusers group name:

Click [OK] to save the change, and you’re done, though you’ll need to log off and back on before the group membership changes take practical effect.

If you prefer doing everything at the command line, just edit /etc/group (as root, of course) and add a :your-username entry to the end of the vboxusers line, which will probably be the last line of the file. In my case, for example, the line ended up reading vboxusers:x:501:hjr -which simply means that user ‘hjr’ is now a member of the vboxusers group. (Again, it’ll take a log off and fresh log on before the new group membership actually takes effect).

Either way, you’re now done and can run the VirtualBox program successfully, with the program launcher being found in Applications > System Tools.

5. USB Support

The version of VirtualBox installed by the above procedure will be unable to access USB 2.0 devices that might be plugged into your physical host. However, this shortcoming can be fixed by installing the “Oracle/VirtualBox Extension Pack”. Download it from the VirtualBox website and then just double-click the file when the download completes. You should see the following appear:

Click the [Install] button there, agree to the license, authenticate as root and all should be done in a matter of seconds. You’re now ready to build and run fully-functional virtual machines.

piix4_smbus 0000.00.07.0: SMBus base address uninitialized - upgrade bios or use force_addr=0xaddr

It doesn’t actually do any harm to the guest (as far as I can tell), so one could perfectly well leave it alone. But it’s possible to get rid of it altogether simply by issuing three commands and editing one configuration file. First:

sudo nano /etc/modprobe.d/blacklist.conf

Add the text

blacklist i2c_piix4

…to the end of the file. Finally, issue the commands:

sudo update-initramfs -u -k all
sudo reboot

When the machine comes back up after that last reboot, you won’t see the error message. What this is doing is simply preventing an attempt to load the i2c_piix4 kernel module. VirtualBox doesn’t emulate the hardware for which this module is actually needed, but Ubuntu doesn’t know that and tries to load it anyway. Blacklisting the module prevents Ubuntu doing that and thus makes the error disappear.