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Mansa Musa was the ruler of the Mali Empire in West Africa. Details recorded here should be sourced; unknown information is left blank.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
 | This article is written like a personal reflection, personal essay, or argumentative essay that states a Wikipedia editor's personal feelings or presents an original argument about a topic. (July 2014) |
The Linux kernel provides multiple interfaces to user-space and kernel-mode code. The interfaces can be classified as either application programming interface (API) or application binary interface (ABI), and they can be classified as either kernel–user space or kernel-internal.
The Linux API includes the kernel–user space API, which allows code in user space to access system resources and services of the Linux kernel.[3] It is composed of the system call interface of the Linux kernel and the subroutines in the C standard library. The focus of the development of the Linux API has been to provide the usable features of the specifications defined in POSIX in a way which is reasonably compatible, robust and performant, and to provide additional useful features not defined in POSIX, just as the kernel–user space APIs of other systems implementing the POSIX API also provide additional features not defined in POSIX.
The Linux API, by choice, has been kept stable over the decades through a policy of not introducing breaking changes; this stability guarantees the portability of source code.[4] At the same time, Linux kernel developers have historically been conservative and meticulous about introducing new system calls.[citation needed]
Much available free and open-source software is written for the POSIX API. Since so much more development flows into the Linux kernel as compared to the other POSIX-compliant combinations of kernel and C standard library,[citation needed] the Linux kernel and its API have been augmented with additional features. Programming for the full Linux API, rather than just the POSIX API, may provide advantages in cases where those additional features are useful. Well-known current examples are udev, systemd and Weston.[5] People such as Lennart Poettering openly advocate to prefer the Linux API over the POSIX API, where this offers advantages.[6]
At FOSDEM 2016, Michael Kerrisk explained some of the perceived issues with the Linux kernel's user-space API, describing that it contains multiple design errors by being non-extensible, unmaintainable, overly complex, of limited purpose, in violation of standards, and inconsistent. Most of those mistakes cannot be fixed because doing so would break the ABI that the kernel presents to the user space.[7]
The system call interface of a kernel is the set of all implemented and available system calls in a kernel. In the Linux kernel, various subsystems, such as the Direct Rendering Manager (DRM), define their own system calls, all of which are part of the system call interface.
Various issues with the organization of the Linux kernel system calls are being publicly discussed. Issues have been pointed out by Andy Lutomirski, Michael Kerrisk and others.[8][9][10][11]
A C standard library for Linux includes wrappers around the system calls of the Linux kernel; the combination of the Linux kernel system call interface and a C standard library is what builds the Linux API. Some popular implementations of the C standard library are
Although the landscape is shifting, amongst these options, glibc remains the most popular implementation, to the point of many treating it as the default and the term equivalent to libc.
As in other Unix-like systems, additional capabilities of the Linux kernel exist that are not part of POSIX:
futex (fast userspace mutex), epoll, splice, dnotify, fanotify, and inotify have been exclusive to the Linux kernel so far.getrandom was introduced in version 3.17 of the Linux kernel mainline[12]memfd was proposed by the kdbus developers[13]
memfd_create was merged into the Linux kernel mainline in kernel version 3.17readahead initiates a file "read-ahead" into page cacheDRM has been paramount for the development and implementations of well-defined and performant free and open-source graphics device drivers without which no rendering acceleration would be available at all, only the 2D drivers would be available in the X.Org Server. DRM was developed for Linux, and since has been ported to other operating systems as well.[14]
 | This article needs attention from an expert in free and open-source software, software or computing. The specific problem is: This section mostly ignores the kernel-userspace ABI (that is very real and important thing) and jumps into userspace-to-userspace APIs. (February 2018) |
The Linux ABI is a kernel–user space ABI. As ABI is a machine code interface, the Linux ABI is bound to the instruction set. Defining a useful ABI and keeping it stable is less the responsibility of the Linux kernel developers or of the developers of the GNU C Library, and more the task for Linux distributions and independent software vendors (ISVs) who wish to sell and provide support for their proprietary software as binaries only for such a single Linux ABI, as opposed to supporting multiple Linux ABIs.
An ABI has to be defined for every instruction set, such as x86, x86-64, MIPS, ARMv7-A (32-Bit), ARMv8-A (64-Bit), etc. with the endianness, if both are supported.
It should be able to compile the software with different compilers against the definitions specified in the ABI and achieve full binary compatibility. Compilers that are free and open-source software are e.g. GNU Compiler Collection, LLVM/Clang.
Many kernel-internal APIs exist, allowing kernel subsystems to interface with one another. These are being kept fairly stable, but there is no guarantee for stability. A kernel-internal API can be changed when such a need is indicated by new research or insights; all necessary modifications and testing have to be done by the author.
The Linux kernel is a monolithic kernel, hence device drivers are kernel components. To ease the burden of companies maintaining their (proprietary) device drivers outside of the main kernel tree, stable APIs for the device drivers have been repeatedly requested. The Linux kernel developers have repeatedly denied guaranteeing stable in-kernel APIs for device drivers. Guaranteeing such would have faltered the development of the Linux kernel in the past and would still in the future and, due to the nature of free and open-source software, are not necessary. Ergo, by choice, the Linux kernel has no stable in-kernel API.[15]
Since there are no stable in-kernel APIs, there cannot be stable in-kernel ABIs.[16]
For many use cases, the Linux API is considered too low-level, so APIs of higher abstraction must be used. Higher-level APIs must be implemented on top of lower-level APIs. Examples:
If a change results in user programs breaking, it's a bug in the kernel. We never EVER blame the user programs.
In fact, the way I see things the Linux API has been taking the role of the POSIX API and Linux is the focal point of all Free Software development. Due to that I can only recommend developers to try to hack with only Linux in mind and experience the freedom and the opportunities this offers you. So, get yourself a copy of The Linux Programming Interface, ignore everything it says about POSIX compatibility and hack away your amazing Linux software. It's quite relieving!
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Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
The Linux kernel provides multiple interfaces to user-space and kernel-mode code. The interfaces can be classified as either application programming interface (API) or application binary interface (ABI), and they can be classified as either kernel–user space or kernel-internal.
NetworkManager is a daemon that sits on top of libudev and other Linux kernel interfaces (and a couple of other daemons) and provides a high-level interface for the configuration of the network interfaces to simplify the use of computer networks on Linux distributions.
Namespaces are a feature of the Linux kernel that partition kernel resources such that one set of processes sees one set of resources, while another set of processes sees a different set of resources. The feature works by assigning the same namespace type to a set of resources and processes, but allowing those namespaces to refer to distinctly isolated environments. This provides the illusion that a process or a process group is the sole user of the system's hardware and software resources. Examples of such resources include process IDs, hostnames, user IDs, file names, network interfaces, and inter-process communication (IPC) mechanisms. Linux namespaces, alongside cgroups (control groups), are the foundational technologies underpinning modern OS-level virtualization and Linux containerization platforms such as Docker, Kubernetes, LXC, and Podman. While cgroups dictate how much of a system's resources a process can use (such as CPU, memory, and disk I/O limits), namespaces dictate what a process is allowed to see and interact with. The term "namespace" is often used to denote a specific type of namespace (e.g., process ID namespace) as well as a particular space of names. A Linux system begins with a single initial namespace of each type, which is shared by all processes. Processes can subsequently create additional namespaces or join existing ones, allowing complex, nested isolation boundaries.
io_uring is a Linux kernel system call interface for storage device asynchronous I/O operations. It addresses performance issues with similar interfaces provided by functions like read()/write() or aio_read()/aio_write() for operations on data accessed by file descriptors.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Brown v. Board of Education in 1954.
