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 Virtual private server


A virtual private server (also referred to as VPS or virtual server, and abbreviated VPS or VDS) is a method of partitioning a physical server computer into multiple servers that each has the appearance and capabilities of running on its own dedicated machine. Each virtual server can run its own full-fledged operating system, and each server can be independently rebooted.


The practice of partitioning a single server so that it appears as multiple servers has long been common practice in mainframe computers, but has seen a resurgence lately with the development of virtualization software and technologies for other architectures.



Overview

The physical server boots normally. It then runs a program that boots each virtual server within a virtualization environment (similar to an emulator). The virtual servers have no direct access to hardware and are usually booted from a disk image.


There are 2 kind of virtualizations: software based and hardware based. In a software based virtualization environment, the virtual machines share the same kernel and actually require the main node's resources. This kind of virtualization normally has many benefits in a web hosting environment because of quota incrementing and decrementing in real time with no need to restart the node. The main examples are Virtuozzo (a product of swsoft.com), HyperVM (a product of lxlabs.com), and openvz which is the core kernel of both virtuozzo and hypervm.


In a hardware based virtualization, the virtualization mechanism partitions the real hardware resources and no burst and/or realtime quota modification is possible. The limits are hard and only modified after a restart. This kind of environment is more secure and is useful in enterprise/commercial usages. Examples include Microsoft Virtual Server, VMWare, and Xen


Uses


Virtual private servers bridge the gap between shared web hosting services and dedicated hosting services, giving independence from other customers of the VPS service in software terms but at less cost than a physical dedicated server. As a VPS runs its own copy of its operating system, customers have superuser-level access to the machine, and can install almost any software that runs on the OS. Certain software does not run well in a virtualized environment, including firewalls, anti-virus clients, and indeed virtualizers themselves; some VPS providers place further restrictions, but they are generally lax compared to those in shared hosting environments. Due to the number of virtualization clients typically run on a single machine, a VPS generally has limited processor time, RAM, and disk space.


Due to their isolated nature, VPSes have become common sandboxes for possibly-insecure public services or update testing. For example, a single physical server might have two virtual private servers running: one hosting the production-level (live) website, and a second which houses a copy of it. When updates to crucial parts of software need to be made, they can be tested in the second VPS, allowing for detailed testing to be conducted without requiring several physical servers.



Virtual private servers are also sometimes employed as honeypots, allowing a machine to deliberately run software with known security flaws without endangering the rest of the server. Multiple honeypots can be quickly set up via VPSes in this fashion.


Virtual private servers are often used by aggressive search engine marketers and web spammers as well.


Virtualization Software


There are several different pieces of software that handle the task of virtualization.


1. User-mode Linux
2. vmware
3. Microsoft Virtual Server
4. qemu
5. VDSmanager
6. Virtualbox
7. xensource
8. parallels
9. OpenVZ
10. HyperVM
11. Virtuozzo
12. FreeVPS
13. Solaris Containers (Zones)


See also


1. mulation
2. Operating system-level virtualization
3. Paravirtualization
4. Virtual machine


Texts are from Wikipedia, the free encyclopedia