Once upon a time I installed Linux on my PC to learn more about system administration. I tried to install a slip server but it didn't work with shadow and mgetty. I had to patch sliplogin and it worked until the new Linux 1.1 releases. No one could tell me what had happened. There was no documentation about changes since the 0.99 kernel except the kernel change summaries from Russ Nelson, but they didn't help me very much in solving problems.
The Linux Programmer's Guide is meant to do what the name implies-- It is to help Linux programmers understand the peculiarities of Linux. By its nature, this also means that it should be useful when porting programs from other operating systems to Linux. Therefore, this guide must describe the system calls and the major kernel changes which have effects on older programs like serial I/O and networking.