Linux Kernel

The Linux kernel is a free and open-source, monolithic, modular, Unix-like operating system kernel. Created by Linus Torvalds on August 25, 1991 (version 0.01 released September 17, 1991) as a personal project while a student at the University of Helsinki in Finland, the Linux kernel has grown into the most widely used operating system kernel in the world, powering Android phones, Chromebooks, servers, supercomputers (100% of the TOP500), embedded devices, IoT devices, and the vast majority of cloud infrastructure. Key features: monolithic kernel: the kernel runs in a single address space (kernel space) with full hardware access. However, it is modular, allowing device drivers and kernel modules to be loaded and unloaded at runtime via the module loader (lsmod, modprobe, insmod). Architecture support: x86 (32-bit and 64-bit), ARM, ARM64, RISC-V, MIPS, PowerPC, SPARC, s390, and more. The kernel supports over 30 distinct hardware architectures. Process management: preemptive multitasking with the Completely Fair Scheduler (CFS), supporting thousands of processes and threads. Namespaces and cgroups (control groups) provide process isolation and resource limits, forming the foundation of container technologies (Docker, Kubernetes). Memory management: virtual memory, demand paging, swap, transparent huge pages, and the OOM (Out of Memory) killer. The memory management subsystem supports memory overcommit and copy-on-write (COW). File systems: supports ext4, XFS, Btrfs, ZFS, F2FS, NTFS, FAT, exFAT, NFS, SMB/CIFS, and over 50 other file systems. The Virtual File System (VFS) provides a unified interface. Networking: TCP/IP, IPv6, netfilter (iptables/nftables), eBPF, and extensive networking protocols. Device drivers: over 50,000 device driver files. Security: SELinux, AppArmor, seccomp. GPL-2.0.