Virtualization is the latest buzz word. You may wonder computers are
getting cheaper every day, why should I care and why should I use
virtualization? Virtualization is a broad term that refers to the
abstraction of computer resources such as:

1. Platform Virtualization
2. Resource Virtualization
3. Storage Virtualization
4. Network Virtualization
5. Desktop Virtualization

This article describes why you need virtualization and list commonly used FOSS and proprietary Linux virtualization software.

Why should I use virtualization?

• Consolidation – It means combining multiple
  software workloads on one computer system. You can run various virtual
  machines in order to save money and power (electricity).
• Testing – You can test various configuration. You
  can create less resource hungry and low priority virtual machines (VM).
  Often, I test new Linux distro inside VM. This is also good for
  students who wish to learn new operating systems and programming
  languages / database without making any changes to working environment.
  At my work place I give developers virtual test machines for testing
  and debugging their software.
• Security and Isolation – If mail server or any
  other app gets cracked, only that VM will be under control of the
  attacker. Also, isolation means misbehaving apps (e.g. memory leaks)
  cannot bring down whole server.

Open Source Linux Virtualization Software

1. OpenVZ is an operating system-level virtualization technology based on the Linux kernel and operating system.
2. Xen is a virtual
   machine monitor for 32 / 64 bit Intel / AMD (IA 64) and PowerPC 970
   architectures. It allows several guest operating systems to be executed
   on the same computer hardware concurrently. XEN is included with most
   popular Linux distributions such as Debian, Ubuntu, CentOS, RHEL,
   Fedora and many others.
3. Kernel-based Virtual Machine (KVM)
   is a Linux kernel virtualization infrastructure. KVM currently supports
   native virtualization using Intel VT or AMD-V. A wide variety of guest
   operating systems work with KVM, including many flavours of Linux, BSD,
   Solaris, and Windows etc. KVM is included with Debian, OpenSuse and
   other Linux distributions.
4. Linux-VServer
   is a virtual private server implementation done by adding operating
   system-level virtualization capabilities to the Linux kernel.
5. VirtualBox
   is an x86 virtualization software package, developed by Sun
   Microsystems as part of its Sun xVM virtualization platform. Supported
   host operating systems include Linux, Mac OS X, OS/2 Warp, Windows XP
   or Vista, and Solaris, while supported guest operating systems include
   FreeBSD, Linux, OpenBSD, OS/2 Warp, Windows and Solaris.
6. Bochs
   is a portable x86 and AMD64 PC emulator and debugger. Many guest
   operating systems can be run using the emulator including DOS, several
   versions of Microsoft Windows, BSDs, Linux, AmigaOS, Rhapsody and
   MorphOS. Bochs can run on many host operating systems, like Windows,
   Windows Mobile, Linux and Mac OS X.
7. User Mode Linux (UML)
   was the first virtualization technology for Linux. User-mode Linux is
   generally considered to have lower performance than some competing
   technologies, such as Xen and OpenVZ. Future work in adding support for
   x86 virtualization to UML may reduce this disadvantage.

Proprietary Linux Virtualization Software

1. VMware ESX Server and VMWare Server
   – VMware Server (also known as GSX Server) is an entry-level server
   virtualization software. VMware ESX Server is an enterprise-level
   virtualization product providing data center virtualization. It can run
   various guest operating systems such as FreeBSD, Linux, Solaris,
   Windows and others.
2. Commercial implementations of XEN available with various features and support.
   • Citrix XenServer :
     XenServer is based on the open source Xen hypervisor, an exceptionally
     lean technology that delivers low overhead and near-native performance.
   • Oracle VM
     : Oracle VM is based on the open-source Xen hypervisor technology,
     supports both Windows and Linux guests and includes an integrated Web
     browser based management console. Oracle VM features fully tested and
     certified Oracle Applications stack in an enterprise virtualization
     environment.
   • Sun xVM
     : The xVM Server uses a bare-metal hypervisor based on the open source
     Xen under a Solaris environment on x86-64 systems. On SPARC systems,
     xVM is based on Sun’s Logical Domains and Solaris. Sun plans to support
     Microsoft Windows (on x86-64 systems only), Linux, and Solaris as guest
     operating systems.
3. Parallels Virtuozzo Containers
   – It is an operating system-level virtualization product designed for
   large-scale homegenous server environments and data centers. Parallels
   Virtuozzo Containers is compatible with x86, x86-64 and IA-64
   platforms. You can run various Linux distributions inside Parallels
   Virtuozzo Containers.