Legally, the LFD420 official PDF is only available to enrolled students. However, The Linux Foundation often releases free sample chapters covering:
Linux Kernel Internals and Development (LFD420): Mastering the Core linux kernel internals and development lfd420 pdf hot
Because user-space debugging tools like standard GDB cannot easily freeze an operating system to inspect it, kernel engineers must rely on specialized instrumentation tools: Legally, the LFD420 official PDF is only available