> particularly how a process for a command is handled through it's life cycle fork(), execve(), waitpid() and friends > also things like how redirection works

> particularly how a process for a command is handled through it's life cycle fork(), execve(), waitpid() and friends > also things like how redirection works dup() ing file descriptors. dup2 is atomic alternative to separately closing a file descriptor and dup'ing to it. xv6 book is freely available on MIT website - it teaches implementation of toy Unix like operating system.. as another commenter mentioned APUE is pretty popular too.