Installing VirtualBox

The (VirtualBox) website has a lot of quality documentation including:

End-user documentation
Technical documentation
Source code repository timeline
List of changes (changelog)

This article will briefly cover the installation process. Both i386 and AMD64 (x86_64) versions are available.

You will need to be the root user for the following tasks. Login to a root shell or "su -" in a terminal window.

Download the RHEL repo config.

Note:
As an alternative, you may choose to download and install individual
RPMS rather than configuring the repository. That procedure is
documented on the VB web site and will not be covered here.

cd /etc/yum.repos.d
wget http://download.virtualbox.org/virtualbox/rpm/rhel/virtualbox.repo

Optionally
add a line "enabled=0" if you do not want the repository to be enabled
by default. This will require adding "--enablerepo virtualbox" to yum
commands to access the repository.

The installation of VB will
require the building of kernel modules. If DKMS (Dynamic Kernel Module
Support) is installed it will be used and will simplify kernel upgrades.
Installing DKMS from RPMforge or EPEL repository is recommended before
installing VirtualBox. Don't forget to configure the yum-priorities
plugin. Installing DKMS will pull in required development dependencies.

yum --enablerepo rpmforge install dkms

<!> A forum user notes that all but the latest version of DKMS from Dell may be buggy.

If DKMS is not used and the development environment and kernel source are not already installed:

yum groupinstall "Development Tools"
yum install kernel-devel

You
may also choose to only install a minimum set of individual development
tool packages (at least gcc and make are required) rather than the
groupinstall which some may consider overkill. Replace "kernel-devel"
with "kernel-PAE-devel" if using a PAE kernel. If you are not using a
standard CentOS kernel, you must acquire and install the source for your
kernel from wherever you got the kernel. Do not try to use VirtualBox
with a Xen kernel, nor to install a Xen kernel in a Guest OS.

Note: For CentOS as a Guest OS the same packages are used to build the "Guest Additions" drivers.

Install the RPM:

yum install VirtualBox-4.1

or for the old versions

yum install VirtualBox-4.0

or

yum install VirtualBox-4.2

The
installer will create the "vboxusers" group and create the necessary
kernel modules if the development environment has been correctly
configured.

For each "username" that will run VirtualBox:

usermod -a -G vboxusers username

or use the GUI Users and Groups tool.