The book contains the full transcript of Software Diagnostics Services training with 16 hands-on exercises on various topics related to Linux API. Our primary goal is to learn Linux API in an accelerated fashion. So, first, we review Linux API fundamentals necessary for software diagnostics. Then we learn various analysis techniques for Linux API exploration. And finally, we see examples of how the knowledge of Linux API helps in diagnostics and debugging. The rough coverage or schedule includes general API aspects that can also be applicable to other operating systems. We also take a radical detour and introduce category theory in the API context. Our coverage is not only theoretical. We also do a tour through different API subsets and classes. An integral part of this training is practical exercises.