How Does Linux Start Up

I upvoted this because I think these sort of tutorials are a good thing. I've learned many things with tutorials like this, which are a great starting point (I used to spend ages reading through tldp howtos etc).

That said, I'd like to see more such descriptive docs about the modern Linux system. I confess, I know very little about how Systemd, dbus, whatever does device management and filesystem mounting, switching of networks in network-manager etc work. I use these daily and I have a vague idea but I would like to read a doc that just opens the boot, points at things and describes them, so to speak. Any recommendations?