freebsd/freebsd-src

★ 9,074CAudience · developerComplexity · 5/5Setup · hard

Mindmap

mindmap
  root((freebsd-src))
    What it is
      Full OS source
      Kernel and userland
      Thirty years active
    Directory layout
      sys kernel source
      bin and tools
      lib system libs
    Third-party code
      contrib components
      gnu GPL code
      cddl licensed
    Use cases
      Study OS internals
      Custom kernel build
      Contribute fixes
    Audience
      Systems developers
      OS researchers

mindmap root((freebsd-src)) What it is Full OS source Kernel and userland Thirty years active Directory layout sys kernel source bin and tools lib system libs Third-party code contrib components gnu GPL code cddl licensed Use cases Study OS internals Custom kernel build Contribute fixes Audience Systems developers OS researchers

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Things people build with this

USE CASE 1

Study the FreeBSD kernel source to understand how an operating system manages memory, processes, and networking at production scale.

USE CASE 2

Build a custom FreeBSD kernel with only the features your embedded device or router needs.

USE CASE 3

Contribute a bug fix or feature to FreeBSD by submitting a pull request through the GitHub mirror.

Tech stack

CAssemblyShellMake

Getting it running

Difficulty · hard Time to first run · 1day+

Building from source requires a supported platform and the FreeBSD Handbook, cross-compilation and custom kernels add significant extra complexity.

In plain English

FreeBSD is a full operating system, meaning it includes not just a kernel (the core that manages hardware) but also the shell, system libraries, networking stack, and standard command-line tools. This repository is the complete source tree for that entire system. It is published here as a read-only mirror, actual development happens through the FreeBSD project's own infrastructure, though the team is experimenting with accepting pull requests through GitHub. FreeBSD has been in continuous development for more than thirty years and powers a wide range of machines: web servers, personal desktops, and embedded devices like routers and storage appliances. Its networking, security, and storage subsystems are well-regarded in the industry, and several large internet companies have historically run it on high-traffic infrastructure. The repository is organized into clearly named subdirectories. The kernel lives in the sys folder. User-facing commands are split across bin, sbin, usr.bin, and usr.sbin. System libraries are in lib. Third-party software that the base system depends on is collected under contrib, gnu, and cddl, each grouped by the license it carries. There is also a stand folder for the boot loader, a crypto folder for cryptographic libraries, and a tests folder for automated testing via a tool called Kyua. Building FreeBSD from source is documented in the project's online handbook, which covers both building the userland (all the non-kernel parts) and compiling a custom kernel. The README points to those guides rather than reproducing them in full. Official pre-built disk images are available from the FreeBSD download site for anyone who does not need to build from source. The project supports multiple CPU architectures and hardware platforms, and a full list is maintained on the FreeBSD website.

Copy-paste prompts

Prompt 1

Walk me through building FreeBSD from source on a supported platform, what commands do I run and roughly how long does it take?

Prompt 2

I want to understand how FreeBSD networking handles TCP connections. Which source files in the freebsd-src repo should I read first?

Prompt 3

How do I compile a custom FreeBSD kernel that removes drivers I do not need to reduce image size for an embedded system?

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