+1 for the implicit sentiment that it may be time for a book-length elucidation of the system, as I was looking around the the same thing — even if it’s
http://0pointer.net/blog/ posts cleaned up and laid out in a systematic (not temporally linear..)
That webpage is unfortunately the best doc I have found on SystemD. Its not unfortunate because it's bad doc, it's good but some is a little out of date. It's that there is nothing better from the makers of SystemD. In the ideal world only "us" system administrators would care about SystemD and it wouldn't be an issue for others. But SystemD is highly pervasive while being difficult to administer. Last I saw, the Amazon AWS linux images had removed it, using SysV-style init like the old days.