37 Facts About Linux kernel

Linux kernel is a free and open-source, monolithic, modular, multitasking, Unix-like operating system kernel.

Linux kernel is provided under the GNU General Public License version 2 only, but it contains files under other compatible licenses.

Linux kernel is deployed on a wide variety of computing systems, such as embedded devices, mobile devices, personal computers, servers, mainframes, and supercomputers.

Linux kernel started with a task switcher in Intel 80386 assembly language and a terminal driver.

At this point, Linux kernel was able to run Bash, GCC, and some other GNU utilities:.

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Torvalds assigned version 0 to the Linux kernel to indicate that it was mainly for testing and not intended for productive use.

The initial success of Linux kernel was driven by programmers and testers across the world.

The fact that Linux is a monolithic kernel rather than a microkernel was the topic of a debate between Andrew S Tanenbaum, the creator of MINIX, and Torvalds.

Linux kernel used to be maintained without the help of an automated source code management system until, in 2002, development switched to BitKeeper.

Linux kernel typically makes use of memory protection and virtual memory and can handle non-uniform memory access, however the project has absorbed µClinux which makes it possible to run Linux kernel on microcontrollers without virtual memory.

Linux kernel is a clone of UNIX, and aims toward POSIX and Single UNIX Specification compliance.

The kernel provides system calls and other interfaces that are Linux-specific.

Therefore, they must always be recompiled whenever a new Linux kernel executable is installed in a system, otherwise they will not be loaded.

In-tree drivers that are configured to become an integral part of the kernel executable are statically linked by the building process.

In-Linux kernel APIs include libraries of low-level common services used by device drivers:.

Modules compiled for a specific version of the Linux kernel cannot be loaded into another version without being recompiled, assuming that the in-Linux kernel API has remained the same at the source level; otherwise, the module code must be modified accordingly.

Linux kernel creates processes by means of the or by the newer system calls.

Linux kernel scheduler is modular, in the sense that it enables different scheduling classes and policies.

Normal tasks, by default, the Linux kernel uses the Completely Fair Scheduler class, introduced in the 2.

PREEMPT_RT code included in mainline Linux kernel provide RT-mutexes, a special kind of Mutex which do not disable preemption and have support for priority inheritance.

The first part is made up of an asynchronous interrupt service routine that in Linux kernel is known as the top half, while the second part is carried out by one of three types of the so-called bottom halves.

The modifications to the kernel were so fundamental that Torvalds viewed the Motorola version as a fork and a "Linux-like operating system".

Linux kernel has been ported to various handheld devices such as Apple's iPhone 3G and iPod.

Rebootless updates can even be applied to the Linux kernel by using live patching technologies such as Ksplice, kpatch and kGraft.

Linux kernel is written in a special C programming language supported by GCC, a compiler that extends in many ways the C standard, for example using inline sections of code written in the assembly language of the target architecture.

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Google moved its production Linux kernel used throughout its datacenters to being built with Clang in 2020.

Each Linux kernel subsystem is assigned a maintainer who is responsible for reviewing patches against the Linux kernel code standards and keeps a queue of patches that can be submitted to Linus Torvalds within a merge window of several weeks.

Patches are merged by Torvalds into the source code of the prior stable Linux kernel release, creating the -rc release candidate for the next stable kernel.

The -rc development release of the kernel goes through regression tests and once it is judged to be stable by Torvalds and the kernel subsystem maintainers a new Linux kernel is released and the development process starts all over again.

In 2014, Sharp backed out of Linux kernel development, saying that "The focus on technical excellence, in combination with overloaded maintainers, and people with different cultural and social norms, means that Linux kernel maintainers are often blunt, rude, or brutal to get their job done".

Torvalds contended that there would never be consistency in the handling of patches because different Linux kernel subsystems have, over time, adopted different development processes.

Mainline Linux kernel has only solid support for a small subset of the many devices that run Linux kernel.

Some operating systems developed for mobile phones initially used heavily modified versions of Linux kernel, including Google Android, Firefox OS, HP webOS, Nokia Maemo and Jolla Sailfish OS.

In 2010, the Linux community criticised Google for effectively starting its own kernel tree:.

Prominent Linux kernel developers have been aware of the importance of avoiding conflicts between developers.

In September 2006, a survey of 29 key Linux kernel programmers indicated that 28 preferred GPLv2 to the then-current GPLv3 draft.

Linux kernel is a registered trademark of Linus Torvalds in the United States, the European Union, and some other countries.