Glossary

Kernel source uses a heavy vocabulary of acronyms and short names. This page defines the terms that recur across the tree and across this wiki. Subsystem-specific jargon (e.g. CFS, EEVDF, BFQ, slub) lives on the relevant subsystem page.

General

• ABI / API — Application Binary Interface (user-visible, stable, never break) vs. in-kernel API (no stability guarantee). See Documentation/process/stable-api-nonsense.rst.
• bzImage / zImage / Image / vmlinuz — Compressed boot image. vmlinux is the uncompressed ELF, bzImage is the x86-style self-extracting big image, Image is the arm64 raw image.
• defconfig — A make defconfig target that produces a .config from a curated list of options under arch/<arch>/configs/.
• DT / DTB / DTS — Device tree, device-tree blob, device-tree source. Used on platforms without ACPI (most ARM, RISC-V, PowerPC).
• initcall — A function annotated with early_initcall/subsys_initcall/device_initcall/etc., run in order during boot from do_initcalls() in init/main.c.
• initramfs — A cpio archive embedded into or loaded with the kernel; the first user-space root file system. See usr/ and init/initramfs.c.
• Kconfig — The kernel's configuration language (declarative). Files named Kconfig define menus, options, and dependencies.
• Kbuild — The recursive make system. See top-level Makefile and Documentation/kbuild/.
• UAPI — User-space API. Headers under include/uapi/ are intended for export to user space and changes there are scrutinized.

Concurrency

• RCU — Read-Copy Update, a synchronization mechanism with very cheap read-side. Implementations live in kernel/rcu/.
• SRCU — Sleepable RCU, allows blocking inside read-side critical sections.
• spinlock_t — Busy-wait lock used in any context. Always disables preemption while held.
• mutex — Sleeping lock for process context only.
• seqlock / seqcount — Sequence counter that lets readers retry rather than block writers.
• completion — One-shot synchronization, complete() / wait_for_completion().
• percpu — Per-CPU data, accessed without locks via this_cpu_* macros and __percpu annotation.
• NMI / IRQ / softirq / tasklet / threaded IRQ — The hierarchy of interrupt contexts, from cannot-be-masked to schedulable.

Memory

• MMU — Memory Management Unit. Translates virtual to physical addresses.
• page — Hardware page (typically 4 KiB on x86, 4/16/64 KiB on arm64).
• THP — Transparent Huge Page. Backed by mm/huge_memory.c.
• slab / slub / kmem_cache — Allocator for small fixed-size objects, on top of the page allocator.
• vmalloc — Allocator returning virtually contiguous, physically discontiguous memory. See mm/vmalloc.c.
• page cache — Cached file contents indexed by (inode, offset). Backbone of the VFS.
• swap / swap cache — Backing store for anonymous pages.
• memcg — Memory cgroup. Implemented in mm/memcontrol.c.
• DAMON — Data Access MONitor, a workload-aware memory monitoring framework under mm/damon/.
• OOM — Out-of-memory. Implemented in mm/oom_kill.c.

Process and scheduling

• task_struct — The kernel's thread descriptor. Defined in include/linux/sched.h.
• CFS / EEVDF — Completely Fair Scheduler / Earliest Eligible Virtual Deadline First. EEVDF replaces CFS as the default fair-scheduling class. Code in kernel/sched/fair.c.
• sched_ext / SCX — BPF-programmable scheduler. See kernel/sched/ext.c.
• PI / RT / Deadline — Priority inheritance, real-time, and SCHED_DEADLINE classes.
• futex — Fast userspace mutex. Kernel side in kernel/futex/.

Storage and I/O

• VFS — Virtual File System. The abstract layer in fs/.
• inode / dentry / superblock / file — The four core VFS objects.
• bio — Block I/O descriptor used by the block layer (block/bio.c).
• request queue / blk-mq — The multi-queue block-layer scheduler.
• DM / MD — Device Mapper / multiple-device (software RAID).
• io_uring — Asynchronous I/O via shared submission/completion rings. See io_uring.

Networking

• socket / sock / sk_buff (skb) — Socket descriptor, kernel-side socket, and packet buffer.
• netdev / net_device — A network interface.
• netns / netnamespace — Network namespace (per-network-stack isolation).
• netfilter — In-kernel firewall hooks. See net/netfilter/.
• XDP — eXpress Data Path. BPF programs run on RX before skb allocation.
• GRO / GSO / TSO — Generic receive/segmentation offload, TCP segmentation offload.

BPF, tracing, security

• BPF / eBPF — In-kernel virtual machine for safe programmability. See kernel/bpf/.
• BTF — BPF Type Format, debug info used by BPF and the verifier.
• ftrace / tracepoint / uprobe / kprobe — Tracing primitives.
• LSM — Linux Security Module. Framework in security/ with SELinux, AppArmor, Smack, IMA, Landlock, IPE.
• seccomp — Syscall filtering. See kernel/seccomp.c.

Architectures and platforms

• arch — One of the 22 directories under arch/. The most active are x86, arm64, riscv, powerpc, and s390.
• vDSO — Virtual dynamic shared object, kernel-provided code mapped into every user process for fast syscalls (gettimeofday, etc.).
• EFI / UEFI — Firmware interface used at boot on x86_64/arm64.
• ACPI — Firmware tables for power and device enumeration on x86 and some arm64 systems.

Build artifacts and conventions

• vmlinux — The fully linked, uncompressed ELF kernel.
• System.map — Symbol map from a kernel build.
• modules.builtin / modules.dep — Lists used by modprobe and depmod.
• SPDX-License-Identifier — The first line of every source file declaring the license. The kernel is GPL-2.0-only with a few LGPL-2.1-or-later and other accepted variations.
• Tested-by / Reviewed-by / Signed-off-by — Trailers in commit messages capturing chain-of-custody. See Documentation/process/submitting-patches.rst.