What Is Linux?

Linux is a free, open-source operating system kernel first released in 1991 by Linus Torvalds, then a student at the University of Helsinki. The kernel forms the core of a family of Unix-like operating systems that together run on a wider range of computing hardware than any other OS family, from embedded microcontrollers and smartphones to supercomputers and cloud data centers. Linux is distributed under the GNU General Public License version 2, which requires that any derivative work also be made available in source form, a licensing structure that has underpinned the growth of a large collaborative development community.

The full operating system environment that most users encounter combines the Linux kernel with the GNU userspace tools, library collections such as glibc, and additional software stacks for graphics, networking, and package management. This combination is formally called GNU/Linux, though "Linux" is widely used as shorthand. The result is a highly modular system whose components can be selected and configured for specific deployment contexts.

Kernel Architecture

As documented at kernel.org, the Linux kernel is a monolithic design with loadable module support: core subsystems including process scheduling, memory management, virtual file systems, and networking are compiled into a single kernel image, while device drivers and file system implementations can be loaded dynamically at runtime as kernel modules. The memory management subsystem supports virtual memory, demand paging, and copy-on-write semantics. The process scheduler has evolved from its original round-robin design through the O(1) scheduler to the Completely Fair Scheduler (CFS), introduced in kernel version 2.6.23 in 2007, which models CPU time allocation as a fair-queuing problem. The networking stack implements IPv4, IPv6, and a variety of transport protocols through a layered socket interface. Linux's portability across processor architectures, including x86, ARM, RISC-V, PowerPC, and MIPS, reflects a design that separates machine-dependent code into architecture-specific subdirectories.

Distributions and Ecosystem

A Linux distribution packages the kernel with a curated set of userspace tools, init systems, package managers, and desktop environments to produce an installable operating system. Major distributions include Debian and its derivatives (Ubuntu, Linux Mint), Red Hat Enterprise Linux and its derivatives (CentOS Stream, AlmaLinux, Rocky Linux), Fedora, Arch Linux, and SUSE Linux Enterprise. Android, which runs on the Linux kernel but uses a distinct userspace, is by installed-device count the most widely deployed Linux-based system. The Linux Foundation, a nonprofit consortium, coordinates the development of the kernel and hosts collaborative projects for cloud infrastructure, networking, and embedded systems. Major technology companies including Google, Intel, IBM, Samsung, and Meta are among the largest contributors to the Linux kernel source tree.

Security and Open-Source Development

Linux kernel development follows a structured process: patches are submitted to mailing lists, reviewed by maintainers responsible for specific subsystems, and merged through Torvalds or a small group of trusted lieutenants into the mainline kernel repository on GitHub. Security vulnerabilities are addressed through a coordinated disclosure process, and stable kernel branches receive backported security fixes for extended maintenance windows. The Linux kernel security documentation describes the security modules framework (LSM), which provides a pluggable interface for mandatory access control policies. SELinux, developed by the NSA, and AppArmor, maintained by Canonical, are the most widely deployed LSM implementations.

Applications

Linux has applications across a wide range of computing contexts, including:

• Cloud infrastructure and container orchestration, where Linux underlies virtually all major cloud provider data centers
• Embedded systems and industrial automation, including automotive control units and network routers
• High-performance computing clusters and scientific simulation environments
• Android-based mobile devices and consumer electronics
• Desktop and workstation environments in scientific research and software development