The Linux kernel at a glance

In short: The Linux kernel is the core of every Linux system. It controls hardware, processes, memory, file systems and networking and mediates between programs and devices.

In more detail: Linus Torvalds started it in 1991 as a hobby project. Today thousands of developers from many companies contribute. The kernel is monolithic but can load modules at run time. Strictly speaking “Linux” means only the kernel, the whole operating system also consists of tools (see Important packages in the Linux base system).

In detail

• Tasks: process scheduler, memory management, drivers, file systems (ext4, Btrfs, XFS), network stack, security (SELinux, AppArmor, namespaces, cgroups).
• Size: more than 30 million lines of code, mostly C, increasingly Rust too.
• Licence: GPL version 2.
• Development: patches by email, maintainers per area, Linus decides on the main branch. See Kernel versions and release cycle.
• User and kernel space: programs run with limited rights and call the kernel through system calls, see System calls and kernel mode.
• Use: servers, smartphones (Android), routers, supercomputers, Steam Deck, cars.
• Show version: uname -r.

See also: Kernel (operating system core), Linux