Microkernel operating system architecture and mach pdf free: Security and resilience issues of monol

Mach (/mɑːk/)[1] is a kernel developed at Carnegie Mellon University by Richard Rashid and Avie Tevanian to support operating system research, primarily distributed and parallel computing. Mach is often considered one of the earliest examples of a microkernel. However, not all versions of Mach are microkernels. Mach's derivatives are the basis of the operating system kernel in GNU Hurd and of Apple's XNU kernel used in macOS, iOS, iPadOS, tvOS, and watchOS.

The project at Carnegie Mellon ran from 1985 to 1994,[2] ending with Mach 3.0, which is a true microkernel. Mach was developed as a replacement for the kernel in the BSD version of Unix, so no new operating system would have to be designed around it. Mach and its derivatives exist within a number of commercial operating systems. These include all using the XNU operating system kernel which incorporates an earlier non-microkernel Mach as a major component. The Mach virtual memory management system was also adopted in 4.4BSD by the BSD developers at CSRG,[3] and appears in modern BSD-derived Unix systems, such as FreeBSD.

microkernel operating system architecture and mach pdf free

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One of the first systems to use a pipe-like system underpinning the operating system was the Aleph kernel developed at the University of Rochester. This introduced the concept of ports, which were essentially a shared memory implementation. In Aleph, the kernel itself was reduced to providing access to the hardware, including memory and the ports, while conventional programs using the ports system implemented all behavior, from device drivers to user programs. This concept greatly reduced the size of the kernel, and allowed users to experiment with different drivers simply by loading them and connecting them together at runtime. This greatly eased the problems when developing new operating system code, which otherwise generally required the machine to be restarted. The general concept of a small kernel and external drivers became known as a microkernel.

The major change between these experimental kernels and Mach was the decision to make a version of the existing 4.2BSD kernel re-implemented on the Accent message-passing concepts. Such a kernel would be binary compatible with existing BSD software, making the system immediately useful for everyday use while still being a useful experimental platform. Additionally, the new kernel would be designed from the start to support multiple processor architectures, even allowing heterogeneous clusters to be constructed. In order to bring the system up as quickly as possible, the system would be implemented by starting with the existing BSD code, and re-implementing it bit by bit as inter-process communication-based (IPC-based) programs. Thus Mach would begin as a monolithic system similar to existing UNIX systems, and evolve more toward the microkernel concept over time.[4]

Under Mach, and like UNIX, the operating system again becomes primarily a collection of utilities. As with UNIX, Mach keeps the concept of a driver for handling the hardware. Therefore, all the drivers for the present hardware have to be included in the microkernel. Other architectures based on Hardware Abstraction Layer or exokernels could move the drivers out of the microkernel.

The main difference with UNIX is that instead of utilities handling files, they can handle any "task". More operating system code was moved out of the kernel and into user space, resulting in a much smaller kernel and the rise of the term microkernel. Unlike traditional systems, under Mach a process, or "task", can consist of a number of threads. While this is common in modern systems, Mach was the first system to define tasks and threads in this way. The kernel's job was reduced from essentially being the operating system to maintaining the "utilities" and scheduling their access to hardware.

Development under such a system would be easier. Not only would the code being worked on exist in a traditional program that could be built using existing tools, it could also be started, debugged and killed off using the same tools. With a monokernel a bug in new code would take down the entire machine and require a reboot, whereas under Mach this would require only that the program be restarted. Additionally the user could tailor the system to include, or exclude, whatever features they required. Since the operating system was simply a collection of programs, they could add or remove parts by simply running or killing them as they would any other program.

By 1986 the system was complete to the point of being able to run on its own on the DEC VAX. Although doing little of practical value, the goal of making a microkernel was realized. This was soon followed by versions on the IBM RT PC and for Sun Microsystems 68030-based workstations, proving the system's portability. By 1987 the list included the Encore Multimax and Sequent Balance machines, testing Mach's ability to run on multiprocessor systems. A public Release 1 was made that year, and Release 2 followed the next year.

Mach received a major boost in visibility when the Open Software Foundation (OSF) announced they would be hosting future versions of OSF/1 on Mach 2.5, and were investigating Mach 3 as well. Mach 2.5 was also selected for the NeXTSTEP system and a number of commercial multiprocessor vendors. Mach 3 led to a number of efforts to port other operating systems parts for the microkernel, including IBM's Workplace OS and several efforts by Apple to build a cross-platform version of the classic Mac OS.[9]

Some of Mach's more esoteric features were also based on this same IPC mechanism. For instance, Mach was able to support multi-processor machines with ease. In a traditional kernel extensive work needs to be carried out to make it reentrant or interruptible, as programs running on different processors could call into the kernel at the same time. Under Mach, the bits of the operating system are isolated in servers, which are able to run, like any other program, on any processor. Although in theory the Mach kernel would also have to be reentrant, in practice this is not an issue because its response times are so fast it can simply wait and serve requests in turn. Mach also included a server that could forward messages not just between programs, but even over the network, which was an area of intense development in the late 1980s and early 1990s.

Most developers instead stuck with the original POE concept of a single large server providing the operating system functionality.[14] In order to ease development, they allowed the operating system server to run either in user-space or kernel-space. This allowed them to develop in user-space and have all the advantages of the original Mach idea, and then move the debugged server into kernel-space in order to get better performance. Several operating systems have since been constructed using this method, known as co-location, among them Lites, MkLinux, OSF/1, and NeXTSTEP/OPENSTEP/macOS. The Chorus microkernel made this a feature of the basic system, allowing servers to be raised into the kernel space using built-in mechanisms.

By the mid-1990s, work on microkernel systems was largely stagnant, although the market had generally believed that all modern operating systems would be microkernel based by the 1990s. The primary remaining widespread uses of the Mach kernel are Apple's macOS and its sibling iOS, which run atop a heavily modified hybrid Open Software Foundation Mach Kernel (OSFMK 7.3) called "XNU"[15] also used in OSF/1.[9] In XNU, the file systems, networking stacks, and process and memory management functions are implemented in the kernel; and file system, networking, and some process and memory management functions are invoked from user mode via ordinary system calls rather than message passing;[16][17] XNU's Mach messages are used for communication between user-mode processes, and for some requests from user-mode code to the kernel and from the kernel to user-mode servers.

Debian is a popular and freely available computer operating system (OS) that uses a Unix-like kernel-- typically Linux -- alongside other program components, many of which come from GNU Project. Debian can be downloaded over the internet or, for a small charge, obtained on CD, DVD, Blu-ray disc or USB flash drive. As open source software, Debian is developed by nearly 1,000 active programmers from around the world who collectively form Debian Project.

An argument for microkernels is that all of the monolithic sub-systems need to synchronize multiple values at one time. In order to do this, they must use locks and will suffer from Amdahl's law when extended to parallel architectures. The counter is that microkernels result in lots of IPC messages.

A monolithic kernel is a kernel architecture where the entire operating system is working in the kernel space and alone as supervisor mode. In difference with other architectures, the monolithic kernel defines alone a high-level virtual interface over computer hardware, with a set of primitives or system calls to implement all operating system services such as process management, concurrency, and memory management itself and one or more device drivers as modules.

A hybrid kernel is a kernel architecture based on combining aspects of microkernel and monolithic kernel architectures used in computer operating systems. The category is controversial due to the similarity to monolithic kernel; the term has been dismissed by some as simple marketing. The traditional kernel categories are monolithic kernels and microkernels (with nanokernels and exokernels seen as more extreme versions of microkernels).

'Monolithic' in this context does not refer to there being a single large executable, and as you say, there Linux supports the dynamic loading of kernel modules at runtime. When talking about kernels, 'monolithic' means that the entire operating system runs in 'privileged' or 'supervisor' mode, as opposed to other types of operating systems that use a type of kernel such as a 'microkernel', where only a minimal set of functionality runs in privileged mode, and most of the operating system runs in user space. 2ff7e9595c