Linux

Linux is a family of open-source Unix-like operating systems built on the Linux kernel. Strictly, "Linux" names only the kernel itself; in everyday use the word also refers to the complete operating systems assembled around it and to the broader ecosystem of distributions, applications, and communities. Because the kernel alone is not a usable system, what people actually run is a distribution – a particular configuration of software packaged around the kernel, almost always including the GNU core utilities and C library that provide the Unix-like userspace. This combination is sometimes written GNU/Linux, a term favored by the GNU project to credit its contribution, though "Linux" remains the common shorthand.

Linux is not UNIX-certified, but it implements the POSIX interfaces and follows Unix conventions, placing it firmly in the Unix-like family. It has become by far the most widely deployed member of that family, powering most web servers, cloud infrastructure, Android devices, and supercomputers.

Linux kernel

The Linux kernel is a free and open-source, Unix-like operating-system kernel first released by Linus Torvalds in 1991. It is the core component of every Linux distribution and of other operating systems such as Android. Written almost entirely in C, it is developed in the open under the GNU General Public License, version 2 only.

The kernel is monolithic: it runs as a single large image in kernel space, in contrast to a microkernel design that keeps the core small and pushes services out into user-space processes. Linux nevertheless achieves modularity through loadable kernel modules (LKMs) – code that can be loaded and unloaded at runtime to add device drivers, filesystems, or other functionality without rebooting. Most device drivers live inside the kernel tree and ship with it, which is a major reason for Linux’s broad hardware support.

Responsibilities centralized in the kernel include process scheduling through its preemptive, priority-based CPU scheduler, memory management (virtual memory, paging, and the slab allocator), the virtual file system (VFS) that presents a uniform interface over many concrete filesystems, and the inter-process communication primitives such as pipes, signals, sockets, and shared memory. The same kernel also implements the namespace and control-group (cgroup) facilities that underpin containerization.

The kernel follows a strict userspace-ABI stability policy, summarized by Torvalds as "we don’t break userspace": a change that would break a previously working userspace program is treated as a bug. This is why binaries compiled years apart, on different distributions, can run on the same kernel. Releases are maintained through a stable and long-term support (LTS) process, with LTS branches kept for several years to give distributions a predictable base. Development happens in public on the Linux Kernel Mailing List (LKML), organized around subsystem maintainers whose trees are pulled into mainline by Torvalds.

Linux distributions

A distribution (or distro) is a complete, installable operating system assembled around the Linux kernel. Beyond the kernel itself, a distribution typically bundles the GNU core utilities and C library, an init system, a package manager together with its repositories, a curated set of prebuilt software packages, and often a default desktop environment and an installer. The kernel is the same project everywhere; what distinguishes distributions is the choices made around it – the package format, the init system, the release cadence, the curated software set, and the intended audience.

Distributions are commonly grouped into families that share an upstream and a package lineage. The Debian family (Debian, Ubuntu, Linux Mint, and many others) shares the apt/dpkg packaging stack. The Fedora/Red Hat family (Fedora, RHEL, CentOS Stream, Rocky Linux, AlmaLinux) shares rpm-based packaging and the dnf/yum tooling. The Arch family (Arch, Manjaro, EndeavourOS) shares pacman and a rolling release, bleeding-edge philosophy. A handful of distributions are independent, built from scratch rather than derived from another, Alpine and Void among them.

Release model is another axis that cuts across families. Some distributions ship numbered point releases on a fixed cadence, such as Ubuntu’s biannual releases; others follow a rolling release with no discrete versions at all. The trade-offs between the two are covered under rolling release.

Consumer-oriented distributions

Debian is one of the oldest operating systems based on the Linux kernel and today it is the foundation distribution for many Linux distributions, including the ubiquitous Ubuntu. Debian is known to be highly stable and reliable, and it is widely used on servers for this reason. For general consumers, a lot of package configuration is required to make it usable – out-of-the-box it’s a pretty bare-bones distribution.

Ubuntu is perhaps the most well-known Linux distribution. Based on Debian, Ubuntu is beginner-friendly, stable, and widely used. It has a large community and excellent support via its parent company, Canonical.

Linux Mint is a polished, easy-to-use alternative to Ubuntu. Based on Debian, it has a more traditional desktop environment that will feel more familiar to users coming from Windows or macOS. The focus is on providing a familiar experience out-of-the-box, with minimal setup required.

openSUSE is known for its powerful system management tools, and it is therefore a good choice for people who want a lot of control over the configuration of their system.

Arch Linux is a lightweight and flexible distribution that is known for its simplicity and customization options. It is popular among advanced users who want to build their system from the ground up. Arch Linux follows a rolling release model, meaning that users always have access to the latest software updates without needing to reinstall or upgrade the entire system.

Manjaro is a user-friendly distribution based on Arch Linux. It offers rolling updates but without all the complexity involved in setting up Arch.

Pop!_OS, developed by System76, is optimized for performance and comes with excellent support for gaming and AI/ML workflows.

Elementary OS focuses on providing a beautiful and intuitive user experience. It is popular among users who appreciate aesthetics and simplicity.

Enterprise-oriented distributions

Fedora is known for integrating the latest Linux features. It’s popular with early adopters, software developers, and other tech enthusiasts who want the latest innovations in Linux. Originally a continuation of the Red Hat Linux project, Fedora is now the upstream source for CentOS Stream and Red Hat Enterprise Linux (RHEL).

Red Hat Enterprise Linux (RHEL) is a commercial distribution that is widely used in enterprise environments. It is known for its stability, security, and long-term support.

CentOS Stream, formerly CentOS (which is a discontinued distribution), is a free and open-source distribution that is based on RHEL. It is popular for servers and enterprise environments due to its stability and long-term support.

AlmaLinux is a community-driven, open-source fork of CentOS.

Rocky Linux is another community-driven, open-source fork of CentOS, created by one of the original founders of CentOS.

Oracle Linux is a free and open-source distribution that is based on RHEL. It is optimized for Oracle software and hardware, but it can be used for general-purpose computing as well.

Specialized distributions

Alpine Linux is an independent Linux distribution, built from scratch rather than being based on an existing distribution like Debian. The most notable characteristic of Alpine is its size. Base images are typically around 5MB, compared to Debian’s 100MB+. This has made Alpine extremely popular for Docker containers where minimizing image size matters. The distribution was originally created for security-focused use cases like routers and firewalls, which explains its minimal approach.

Alpine uses musl libc instead of the more common glibc that Debian uses. This makes Alpine significantly lighter but can occasionally cause compatibility issues with software expecting glibc.

For package management, Alpine has apk (Alpine Package Keeper), while Debian uses apt/dpkg. Alpine’s packages are generally smaller and more minimal.

Alpine uses OpenRC as its init system, whereas Debian-based systems use systemd by default.

Alpine also uses BusyBox for many core utilities instead of GNU coreutils, which contributes to its small footprint but means some commands may have slightly different options or behaviors than you’d expect on Debian or other mainstream distributions.

NixOS takes a markedly different approach to package management. The entire system configuration – packages, services, and users – is declared in a single functional expression evaluated by the Nix package manager, which makes the system fully reproducible and upgrades atomic, with rollbacks available should a change go wrong.

Tails is a portable, live distribution focused on privacy and anonymity. It is designed to boot from a USB stick, run entirely in RAM, and leave no trace on the host machine, routing all network traffic through the Tor network.

Kali Linux is a Debian-based distribution built for penetration testing and security auditing, preloaded with tools for vulnerability analysis, network sniffing, and exploitation.

Linux desktop environments

A desktop environment (DE) is the graphical layer that sits above the kernel and userspace to provide the familiar windows, icons, menus, and pointer desktop experience. It bundles a window manager, a file manager, settings panels, and a set of default applications. Most distributions ship a default DE but allow others to be installed, so the same distribution can be run under different DEs. The major DEs in the Linux ecosystem include:

  • GNOME. The default on Fedora, Ubuntu, and others; a modern, opinionated shell with a focus on keyboard-driven workflow and minimal chrome.
  • KDE Plasma. The default on Kubuntu, openSUSE, and others; highly configurable and traditional in layout.
  • Xfce. A lightweight and stable DE suited to older or lower-spec hardware.
  • Cinnamon. Linux Mint’s native DE, offering a Windows-like layout.
  • MATE. A continuation of the classic GNOME 2 line.

Linux package managers

Each distribution family ships its own native package manager, which fetches software from the distribution’s curated repositories and resolves dependencies:

  • APT. Debian and its derivatives (Ubuntu, Mint).
  • DNF. Fedora and the Red Hat family.
  • Pacman. Arch and its derivatives.
  • Zypper. openSUSE.

Alongside the distro-native managers, a newer generation of universal package formats – chiefly Flatpak, Snap, and AppImage – bundles an application together with its dependencies so that a single artifact runs across distributions. These trade the integration and shared-library efficiency of native packages for portability and sandboxing. Flatpak is oriented toward desktop applications and distributed through Flathub; Snap, backed by Canonical, covers both desktop and server workloads; AppImage is a single self-contained, runnable file. Their rise has eased cross-distribution packaging for application authors, at the cost of larger downloads and duplication of libraries. Nix, from NixOS, takes a different route still, managing packages as immutable store paths referenced by a functional configuration language.

Security layers

Linux distributions commonly layer a mandatory access control (MAC) framework on top of the kernel’s discretionary file permissions, confining programs with policies that the programs themselves cannot override:

  • SELinux. The default on Fedora, CentOS Stream, and RHEL; enforces type-enforcement policies that label every process and object and govern the interactions between them.
  • AppArmor. The default on Ubuntu and SUSE; confines programs with path-based profiles, generally considered simpler to author than SELinux policy.

A complementary approach is taken by distributions such as Talos and Flatcar, which mount the system image read-only and apply changes only through atomic, verifiable updates. The running system cannot be tampered with at runtime, which makes the security story about immutability and reproducibility rather than runtime confinement.

See also