Linux Glossary

Also: control groups · cgroup v2

cgroups (control groups) are a Linux kernel feature that limits, accounts for, and isolates the resource usage — CPU, memory, disk I/O, network — of a group of processes.

Also: Linux container · OCI container · Docker container

A container is a process or group of processes running in isolation on a shared kernel, using namespaces for visibility isolation and cgroups for resource limits, packaged with its own filesystem and dependencies.

Also: init · PID 1 · systemd · SysVinit

The init system is the first user-space process started by the kernel at boot, running as PID 1, responsible for starting and supervising all other system services and handling shutdown.

Also: Linux kernel · monolithic kernel · kernel space

The kernel is the core of an operating system, responsible for managing memory, scheduling processes, and mediating all access between software and hardware. The Linux kernel is the component that makes a system 'Linux'.

Also: LKM · loadable kernel module · driver module

A kernel module is a piece of code that can be loaded into and unloaded from a running Linux kernel on demand, extending its functionality — most commonly with device drivers — without requiring a reboot or recompilation.

Also: distro · Linux distro

A Linux distribution is a complete operating system built around the Linux kernel, bundling it with system libraries, a package manager, default utilities, and a curated set of software, along with policies for how all of it is maintained and updated.

Also: LTS · LTS release · extended support

Long-term support (LTS) designates a software release that will receive security patches and critical bug fixes for an extended period — typically several years — without introducing new features or breaking changes.

Also: Linux namespaces · PID namespace · network namespace

A Linux namespace is a kernel feature that gives a process an isolated view of a particular system resource — process IDs, network interfaces, mount points, hostnames — forming the primary isolation mechanism behind containers.

Also: FOSS · free software · OSS

Open source software is software distributed under a licence that grants anyone the right to use, inspect, modify, and redistribute the source code, subject to conditions defined by that licence.

Also: apt · dnf · pacman · dependency resolution

A package manager is the tool that installs, updates, configures, and removes software on a Linux system, resolving dependencies automatically and verifying package integrity through cryptographic signatures.

Also: seccomp-bpf · syscall filtering

seccomp is a Linux kernel feature that restricts which system calls a process may make, reducing the kernel attack surface available to a compromised or untrusted program.

Also: UEFI Secure Boot · verified boot

Secure Boot is a UEFI firmware feature that verifies the cryptographic signature of each component in the boot chain — bootloader, kernel, and drivers — refusing to execute anything not signed by a trusted key.

Also: SELinux · AppArmor · MAC · mandatory access control

SELinux and AppArmor are Linux mandatory access control systems that confine processes to explicitly permitted actions, so that even a process running as root is limited to what its policy allows.

Also: syscall · kernel API

A system call is the mechanism by which a user-space program requests a service from the kernel — such as opening a file, allocating memory, or sending network data — crossing the privilege boundary between application and kernel.

Also: systemctl · journald · systemd unit

systemd is the init system and service manager used by most major Linux distributions, handling service startup and supervision, logging, device management, and system state through a unified set of components.

Also: Wayland compositor · Wayland protocol

Wayland is a display server protocol for Linux designed to replace the X Window System, in which a single compositor handles rendering, input, and window management rather than the client-server split X uses.

Also: X Window System · Xorg · X server

X11 is the long-standing display server protocol for Unix-like systems, providing a network-transparent client-server architecture in which applications connect to an X server that manages display output and input devices.