Understanding the Linux Kernel Directory Structure.

The Linux kernel source tree can seem daunting at first, especially when you’re just getting started. This guide breaks down the top-level structure of the kernel source directory, so you know where to look for what.

📂 Top-Level Directory Structure of Linux Kernel (v6.1)

Name Type Description
COPYING File GPL license text (legal terms for usage and distribution).
CREDITS File List of contributors to the Linux kernel with roles and contacts.
Kbuild File Build system metadata; included by many Makefiles across subdirs.
Kconfig File Global configuration menu entry point (used in make menuconfig).
LICENSES/ Dir SPDX license texts used in various parts of the kernel.
MAINTAINERS File List of maintainers per subsystem + file patterns for reporting bugs.
Makefile File Top-level Makefile: entry point for building the kernel.
README File Getting-started documentation for building and booting the kernel.
System.map File Kernel symbol table (maps symbols to addresses). Useful for debugging.
Module.symvers File Symbol versioning info for external modules to ensure compatibility.
arch/ Dir Architecture-specific code (x86, ARM, RISC-V, etc.).
block/ Dir Block layer (e.g., block devices, request queues, I/O scheduling).
certs/ Dir Code and config for kernel module signature verification.
crypto/ Dir Cryptographic algorithms and APIs used in-kernel.
drivers/ Dir All device drivers (USB, GPU, network cards, etc.).
fs/ Dir File systems (ext4, xfs, NFS, FUSE, VFS layer, etc.).
include/ Dir Header files (include/linux/, include/uapi/, etc.). Used by kernel and modules.
init/ Dir Code run during kernel initialization (early boot).
io_uring/ Dir Fast async I/O subsystem introduced in newer kernels.
ipc/ Dir System V IPC mechanisms: semaphores, message queues, shared memory.
kernel/ Dir Core kernel code: scheduler, syscalls, fork/exec, timers, locking, etc.
lib/ Dir Generic helper libraries (math, RCU, string handling, bitmaps, etc.).
mm/ Dir Memory management subsystem (VM, page cache, slab, etc.).
net/ Dir Networking stack (TCP/IP, sockets, routing, protocols).
rust/ Dir [Optional] Rust language support in kernel (emerging in recent kernels).
samples/ Dir Sample kernel modules and features (e.g., BPF, tracepoints, etc.).
scripts/ Dir Scripts for building, checking, and preparing kernel modules.
security/ Dir Security modules: SELinux, AppArmor, Smack, LSM framework.
sound/ Dir Audio subsystem (ALSA, OSS, SoC audio).
tools/ Dir User-space tools (e.g., perf, bpf, selftests).
usr/ Dir Initramfs image creator (usr/initramfs_data.cpio). Used during kernel build.
virt/ Dir Virtualization support (KVM, guest hypervisors).

🧱 Generated Build Artifacts (After make)

File/Folder Type Description
vmlinux File Uncompressed kernel image (ELF format). Contains full kernel.
vmlinux.o File Linked object file (intermediate format before final vmlinux).
vmlinux.a File Archive of compiled objects before linking into vmlinux.o.
vmlinux.symvers File Symbol version mapping (used by external modules).
built-in.a File Statically linked object archive (combined .o files).
modules.order File List of modules compiled and their order of loading.
modules.builtin File List of built-in modules (not .ko, but statically linked).
modules.builtin.modinfo File Metadata of built-in modules for modinfo, depmod.

✅ Pro Tips

  • Run tree -L 1 inside the kernel root directory to visualize the structure.
  • Most of your time will be spent inside:
    • kernel/, arch/x86/, include/linux/, arch/x86/entry/syscalls/ — for syscall and core development.
    • drivers/ and fs/ — for device drivers and file systems.
    • tools/ — for advanced tools like perf, bpf, and cpupower.

This directory map is your compass when navigating the massive Linux kernel. Happy hacking! 🐧💻