ROLE OF VIRTUAL MACHINE IN OPERATING SYSTEM

Transcription

1 ROLE OF VIRTUAL MACHINE IN OPERATING SYSTEM Sweety Sen, Sonali Samanta B.Tech, Information Technology, Dronacharya College of Engineering, Gurgaon, India Abstract- In this paper, we are concentrating about the role of Virtual Machine with Environment. Virtual machine helps us to operate multiple OS on the same hardware. At the same time.virtual machine can support individual processes or complete system. Depending on the abstraction level where virtualization occurs. Virtual Machine Operating System creates illusion of multiple processors each capable of executing independently. Virtual machines are separated into two major categories, based on their use and degree of correspondence to any real machine. The Operating System actually running on the hardware is called host operating system and the operating system running in the simulated environment is called guest operating system. Index Terms- Virtual machine, Host OS, Guest OS. I. INTRODUCTION OF OPERATING SYSTEM (OS) An operating system is a software program that enables the computer hardware to communicate and operate with the computer software. Without a computer operating system, a computer and software programs would be useless. Application programs usually require an operating system to function. The operating system provides two main functions. The first function is managing the basic hardware operations. The control of input and output, storage space, detecting equipment failure, and management of storage are just some of the responsibilities of the Operating System. The second function is managing and interacting with the applications software. It takes over the tasks of printing and saving data. To provide an environment for a computer user to execute programs. Basic Function of OS: Process Management : The Operating System also Treats the Process Management means all the Processes those are given by the user or the Process those are System s own Process are Handled by the Operating System. The Operating System will Create the Priorities for the user and also Start or Stops the Execution of the Process and Also Makes the Child Process after dividing the Large Processes into the Small Processes. Memory Management: Operating System also manages the Memory of the Computer System means provide the Memory to the Process and Also deallocate the Memory from the Process. And also defines that if a Process gets completed then this will deallocate the Memory from the Processes. Device Management: OS manages device communication via their respective drivers. It Allocates and De-allocates the device in the efficient way. It also decides which process gets the device when and for how much time. File Management: A file system is normally organized into directories for easy navigation and usage. These directories may contain files and other directions. OS Keeps track of information, location, uses, status etc. The collective facilities are often known as file system. It Decides who gets the resources and also allocates and de-allocates the resources. II. INTRODUCTION TO VIRTUAL OPERATING SYSTEM The idea of a virtual operating system is to provide standard versions of the following- 1. Operating system primitives accessible through programming languages 2. The utility programs such as compilers, linkers and editors 3. The command language or means by which users access system resources from a terminal based on organizational requirements. VM (operating system) Introduction: VM (often: VM/CMS) is a family of IBM virtual machine operating systems used on IBM mainframes System/370, System/390, zseries, System z and compatible systems, including the Hercules emulator for personal computers. The first version, released in 1972, was VM/370, or officially Virtual Machine Facility/370. This was a System/370 reimplementation of earlier CP/CMS operating system. Milestone versions included VM/SP.The current version, z/vm, is still widely IJIRT INTERNATONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 217

2 used as one of the main full virtualization solutions for the mainframe market. Overview: The heart of the VM architecture is a control program or hypervisor called VM-CP (usually: CP; sometimes, ambiguously: VM). It runs on the physical hardware, and creates the virtual machine environment. VM-CP provides full virtualization of the physical machine including all I/O and other privileged operations. It performs the system's resource-sharing, including device management, dispatching, virtual storage management, and other traditional operating system tasks. Each VM user is provided with a separate virtual machine having its own address space, virtual devices, etc., and which is capable of running any software that could be run on a standalone machine. A given VM mainframe typically runs hundreds or thousands of virtual machine instances. VM-CP began life as CP-370, a reimplementation of CP-67, itself a reimplementation of CP-40. Running within each virtual machine is another, "guest" operating system. This might be: CMS ("Conversational Monitor System", renamed from the "Cambridge Monitor System" of CP/CMS). Its official name is VM- CMS (confusing, since VM is commonly called VM/CMS). Most virtual machines run CMS, a lightweight, single-user operating system. Its interactive environment is comparable to that of a single-user PC, including a file system, programming services, device access, and command-line processing. A mainstream operating system. IBM's mainstream operating systems (i.e. the MVS or DOS/VSE families) can be loaded and run without modification. The VM hypervisor treats guest operating systems as application programs with exceptional privileges - it prevents them from using privileged instructions but simulates privileged instructions on their behalf. Most mainframe operating systems terminate a normal application which tries to usurp the operating system's privileges. Another copy of VM. A "second level" instance of VM can be fully virtualized inside a virtual machine. This is how VM development and testing is done. (A "secondlevel" VM can potentially implement a different virtualization of the hardware. This technique was used to develop S/370 software before S/370 hardware was available, and it has continued to play a role in new hardware development at IBM. The literature cites practical examples of virtualization five levels deep.levels of VM below the top are also treated as applications but with exceptional privileges. A copy of the mainframe version of AIX or Linux. In the mainframe environment, these operating systems often run under VM, and are handled like other guest operating systems. A specialized VM subsystem. Several non- CMS systems run within VM-CP virtual machines, providing services to CMS users such as spooling, intercrosses communications, and specialized device support. They operate "behind the scenes", extending the services available to CMS without adding to the VM- CP control program. By running in separate virtual machines, they receive the same security and reliability protections as other VM users. Examples include: RSCS ("Remote Spooling and Communication Subsystem", aka VNET) communication and information transfer facilities between virtual machines RACF ("Resource Access Control Facility") a security system GCS ("Group Control System"), which provides a limited simulation of the MVS API. History: The early history of VM is described in the articles CP/CMS and History of CP/CMS. VM/370 was a reimplementation of CP/CMS, and was made available in 1972 as part of IBM's "System/370 Advanced Function" announcement (which added virtual memory hardware and operating systems to the System/370 series). Early releases of VM through VM/370 Release 6 continued in open source, and today are considered to be in the public domain. This policy ended in the late 1970s with the chargeable VM/SE and VM/BSE upgrades and in 1980 with VM/System Product (VM/SP). However, IBM continued providing updates in source form for existing code for many years. VM remained an important platform within IBM, used for operating system development and timesharing use; but for customers it remained IBM's "other operating system". The OS and DOS families remained IBM's strategic products, and customers were not encouraged to run VM. Those that did formed close working relationships, continuing the community-support model of early CP/CMS users. In the meantime, the system struggled with political infighting within IBM over what resources should be available to the project, as compared with other IBM efforts. A basic "problem" with the system was seen at IBM's field sales level: VM/CMS demonstrably reduced the amount of hardware needed to support a given IJIRT INTERNATONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 218

3 number of time-sharing users. IBM was, after all, in the business of selling computer systems. Virtual Memory: A Virtual Memory has the advantage of allowing more processes to run than the allowed memory size. This is achieved by only including parts of processes that are necessary to run in memory and the rest on disk. The absolute minimum part of a process that must always be in memory is called its working set. Usually, a program doesn't need to have its entire binary file in memory to run when it is performing a task that only uses part of its file. What this means is that, say, a 16MB program could happily run on a machine with only 4MB of memory. Virtual Machine: A virtual machine (VM) is a software implementation of a machine (for example, a computer) that executes programs like a physical machine. A virtual machine is a completely isolated guest operating system installation within a normal host operating system. Virtual Machine Operating System creates illusion of multiple processors each capable of executing independently. Virtual machines are separated into two major categories, based on their use and degree of correspondence to any real machine:- System Virtual Machines: A system virtual machine provides a complete system platform which supports the execution of a complete operating system. These usually emulate an existing architecture, and are built with the purpose of either providing a platform to run programs where the real hardware is not available for use or of having multiple instances of virtual machines leading to more efficient use of computing resources, both in terms of energy consumption and cost effectiveness, or both. A virtual machine can provide an instruction set architecture (ISA) that can vary from the host hard drive, such as visual display formatting of adjunct software management tools, font characteristics, and html formatting. Application provisioning, maintenance, high availability and disaster recovery are inherent in the virtual machine software selected. Process Virtual Machines: A process VM, sometimes called an application virtual machine, or Managed Runtime Environment(MRE), runs as a normal application inside a host OS and supports a single process. It is created when that process is started and destroyed when it exits. Its purpose is to provide a platform-independent programming environment that abstracts away details of the underlying hardware or operating system, and allows a program to execute in the same way on any platform. This type of VM has become popular with the Java programming language, which is implemented using the Java virtual machine. Fig.1- Process and system VMs. (a) In a process VM, virtualizing software translates a set of OS and user-level instructions composing one platform to those of another. (b) In a system VM, virtualizing software translates the ISA used by one hardware platform to that of another. Advantages of a virtual machine include: Allows multiple operating system environments on a single physical computer without any intervention Virtual machines are widely available and are easy to manage and maintain. Offers application provisioning and disaster recovery options Drawbacks of virtual machines include: They are not as efficient as a physical computer because the hardware resources are distributed in an indirect way. Multiple VMs running on a single physical machine can deliver unstable performance Working Of Virtual Machine OS: A virtualmachine monitor is a software layer that runs on a host platform and provides an abstraction of a complete computer system to higher-level software. The software running above the virtualmachine abstraction is called guest software (operating system and applications).our goal for this paper is to examine and reduce the performance overhead associated with running a VMM on a host operating system. Building it on a standard Linux host operating system leads to an order of magnitude performance degradation IJIRT INTERNATONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 219

4 compared to running outside a virtual machine (a standalone system). However, we find that a few simple extensions to the host operating system reduces virtualization overhead to 14-35% overhead, which is comparable to the speed of virtual machines that run directly on the hardware Fig.2- Virtual-machine structures Fig. 3- Guest application system call This picture shows the steps UMLinux takes to transfer control to the guest operating system when a guest application process issues a system call. The mmap call in the SIGUSR1handler must reside in guest user space. For security, the rest of the SIGUSR1 handler should reside in guest kernel space. The current UMLinux implementation includes an extra section of trampoline code to issue the mmap; this trampoline code is started by manipulating the guest machine process s context and finishes by causing a breakpoint to the VMM process; the VMM process then transfers control back to the guest-machine process by sending a SIGUSR1 1. Guest application issues system call; intercepted by VMM process via ptrace 2. VMM process changes system call to no-op (getpid) 3. Getpid returns; intercepted by VMM process 4. VMM process sends SIGUSR1 signal to guest SIGUSR1 handler 5. Guest SIGUSR1 handler calls mmap to allow access to guest kernel data; intercepted by VMM process 6. VMM process allows mmap to pass through 7. mmap returns to VMM process 8. VMM process returns to guest SIGUSR1 handler, which handles the guest application s system call. Architecture of Virtual Machine Despite their incredible complexity, computer systems exist and continue to evolve because they are designed as hierarchies with well-defined interfaces that separate levels of abstraction. Using well-defined interfaces facilitates independent subsystem development by both hardware and software design teams. The simplifying abstractions hide lower-level implementation details, thereby reducing the complexity of the design process. Figure 1a, shows an example of abstraction applied to disk storage. The operating system abstracts hard-disk addressing details for example, that it is comprised of sectors and tracks so that the disk appears to application software as a set of variable-sized files. Application programmer scan then create, write, and read files without knowing the hard disk s construction and physical organization. Unlike abstraction, virtualization does not necessarily aim to simplify or hide details. For example, in Figure1b, virtualization transforms a single large disk into two smaller virtual disks, each of which appears to have its own tracks and sectors. Virtualization software uses the file abstraction as an intermediate step to provide a mapping between the virtual and real disks. A write to a virtual disk is converted to a file write (and therefore to a real disk write). Note that the level of detail provided at the virtual disk interface the sector/track addressing is no different from that for a real disk; no abstraction takes place. Fig.4- Abstraction and virtualization applied to disk storage.(a) Abstraction provides a simplified interface to underlying resources. (b) Virtualization provides a different interface or different resources at the same abstraction level. III. ARCHITECTED INTERFACES Fig. 5 shows some important interfaces and implementation layers in a typical computer system. Three of these interfaces at or near the HW/SW boundary the instruction set architecture, the application binary interface, and IJIRT INTERNATONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 220

5 the application programming interface are especially important for VM construction. Fig.5- Computer system architecture. Key implementation layers communicate vertically via the instruction set architecture (ISA), application binary interface (ABI), and application programming interface (API). Instruction set architecture: The ISA marks the division between hardware and software, and consists of interfaces 3 and 4 in Fig. 2 Interface 4 represents the user ISA and includes those aspects visible to an application program. Interface 3, the system ISA, is a superset of the user ISA and includes those aspects visible only to operating system software responsible for managing hardware resources. Application binary interface: Program access to the hardware resources and services available in a system through the user ISA (interface 4) and the system call interface (interface 2). The ABI does not include system instructions; rather, all application programs interact with the hardware resources indirectly by invoking the operating system s services via the system call interface. System calls provide a way for an operating system to perform operations on behalf of a user program after validating their authenticity and safety. Application programming interface: The API gives a program access to the hardware resources and services available in a system through the user ISA (interface 4) supplemented with high-level language (HLL) library calls (interface 1). Any system calls are usually performed through libraries. Using an API enables application software to be ported easily, through recompilation, to other systems that support the same API. Advantages: 1. Multiple OS environments can exist simultaneously on the same machine, isolated from each other. 2. Virtual machine can offer an instruction set architecture that differs from real computer's. 3. Easy maintenance, application provisioning, availability and convenient recovery. Disadvantages: 1. Virtual machine is not that efficient as a real one when accessing the hardware. 2. When multiple virtual machines are simultaneously running on a host computer, each virtual machine may introduce an unstable performance, which depends on the workload on the system by other running virtual machines. 3. The host OS required a separate host user process to control the main guest-machine process, and this generated a large number of host context switches. Applications: Try new operating systems- If you want to try a new OS on same hardware. Put together a VM and build Ubuntu on it. Suddenly, you can launch and try dozens of operating systems without much hassle. Test your software- When we create new software like web application, application program etc. we can test that software on different OS by using the VMware. Weather the software run efficiently on different OS or not. Small Biz disaster recovery- This isn t highly recommended, but it d work if you re bootstrapping. Say you re hosting a few web servers with your amazing app on them. Your house gets hit by lightning. Your site is off the air. Now, imagine that scenario but you ve got virtual backups of the latest build and configuration ready to install and deploy wherever else you ve got a point of presence. Poof. You re online again. Build kid boxes- Build Edubuntu (a kid flavored Ubuntu) on a virtual machine for the kids (the specs I mention above are for \heavy users, but you could get away with a lot less if you only ran ONE VM). If (when) things go sour from one too many tweaks, just drop the VM and restore from your pristine copy. Talk about easy. You can get them back on the net in less than 10 minutes. Backup your system- When you get ready to move from XP to Vista, you can use VMware to make a backup of your old system. If things go horribly sour, you could have the VM version up and running in short order. By the way, you can have TWO servers and have a copy of the VM on both. This would give you even more business continuity, should something happen to the server. IJIRT INTERNATONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 221

6 Save Legacy Systems- Offices and data centers often have an old box around that just can t be mucked with. There s additional software you can use to do what s called a P2V switch, a physicaltovirtual conversion, where the old box s image gets copied onto the virtual machine files, and thus, gives you a hopefullyoperational clone of the old grandpa box in the corner. Conclusion and Future Work: In the future, there can be reduction in the size of the host operating system used to support a VMM. Much of the code in the host OS can be eliminated, because the VMM uses only a small number of system calls and abstractions in the host OS. Reducing the code size of the host OS will help make VM a fast and trusted base for future virtualmachine services. In this presentation we examine Virtual Machine on the basis of operating system. We study how there is actual working between Operating system and virtual machine and how we can access multiple operating system on same hardware. Virtual Machine in Technology: Operating System (VM) An IBM pseudo- operating system hypervisor running on IBM 370, ESA and IBM 390 architecture computers. VM comprises CP( Control Program ) and CMS ( Conversational Monitor System ) providing Hypervisor and personal computing environments respectively. VM became most used in the early 1980s as a Hypervisor for multiple DOS/VS and DOS/VSE systems and as IBM's internal operating system of choice. It declined rapidly following widespread adoption of the IBM PC and hardware partitioning in microcode on IBM mainframes after the IBM VM has been known as VM/SP (System Product, the successor to CP/67), VM/XA, and currently as VM/ESA (Enterprise Systems Architecture). VM/ESA is still in used in 1999, featuring a web interface, Java, and DB2. It is still a major IBM operating system. 2. A software emulation of a physical computing environment. The term gave rise to the name of IBM's VM operating system whose task is to provide one or more simultaneous execution environments in which operating systems or other programs may execute as though they were running "on the bare iron", that is, without an eveloping Control Program. A major use of VM is the running of both outdated and current versions of the same operating system on a single CPU complex for the purpose of system migration, thereby obviating the need for a second processor. REFERENCES [1] tem) [2] machine [3] tem). [4] Brinch Hansen P. (1973) Operating System Principles. [5] Kernighan. Software Practice and Experience, 5 (4), [6] =667&q=virtual+machine+architecture+operating+ system&revid= &sa=x&ei=73qevkw 4B9OA8gXy_IL4Ag&ved=0CHsQ1QIo [7] ual-machine-vm [8] "VM/SP Announced 1980/02/11, GA 1980/12/12" Elliott, Jim ( ). "The Evolution of IBM Mainframes and VM" (PDF). SHARE Session Retrieved [9] release history 1. An abstract machine for which an interpreter exists. Virtual machines are often used in the implementation of portable executors for high-level languages. The HLL is compiled into code for the virtual machine (an intermediate language) which is then executed by an interpreter written in assembly language or some other portable language like C. Examples are Core War, Java Virtual Machine, OCODE, OS/2, POPLOG, Portable Scheme Interpreter, Portable Standard Lisp, Parallel Virtual Machine, Sequential Parlog Machine, SNOBOL Implementation Language, SODA, Smalltalk. IJIRT INTERNATONAL JOURNAL OF INNOVATIVE RESEARCH IN TECHNOLOGY 222