I've been meaning to put down my thoughts about SystemD for the HPR community for some while, so here goes.

I want to say that I am not a SystemD hater. When SystemD was a hot topic of debate, many became irrational over it, but I want to start by saying that I don't think it's a bad technology. I think it is a rather good technology. I just don't want it on my personal computer. So I would like to run things down in this order: what is it (as in, what is it really,) what makes it a good technology, why I don't want it now (but might later,) and a few tips for you if you decide that you don't want it currently.

SystemD Is not an init system. SystemD includes an init system. SystemD Init was faster than SysVInit, but SystemD Init isn't the fastest init system, and SysVInit now has a parallelization helper, at least on Debian.

So, if SystemD Init is not SystemD, than what is SystemD? To understand this we must first understand something about Linux. Linux operates under a model where there are root processes, and there are user processes. These two kinds of processes are usually called "layers." SystemD is actually a third layer, that can be called a system layer. So when SystemD is added to a Linux system, that changes the system so that there are three layers, a root layer, a user layer, and a system layer. As such, you now ask SystemD to set how the system runs. This is why SystemD includes things like an init system, because if you want to change what the system is running, you ask SystemD to change it. SystemD then messages an appropriate system to implement the change, like messaging its init system to bring up or bring down a system daemon. Once you play out this in your head a bit, you really realize that SystemD acts more like a message passing system in this regard.

So why do I say SystemD is a good technology? Because this can standardize system control. Without SystemD a fleet of computers becomes like individual fingerprints or unique snowflakes. If you manage many computers, as many professional IT people do, you want them to all run the same, all have the same profiles and general configurations. So if you have a bunch of computers you are running, you can run a lot more if they are all run the same way. If your job requires you to run 10,000 webservers, you want them to run identically because it is impossible to keep an understanding of 10,000 unique configurations in a human head.

SystemD really shines in its support of virtualization as well. So to speak of servers, I used to run an email server for a few friends. Each of us had a userid and number as unix users. The mapping of unix userids and postfix userids can get confusing when it gets big. Thanks to SystemD's virtualization work, you can actually put a service like email into a namespace situation so that it has only the users root and the daemon user id (like "postfix"), so SystemD greatly enhances security for server installations. This might help explain its dominance in linux distributions that have been traditionally server-centric, such as debian and redhat.

So why don't I don't want it? Well, I've been doing a lot of talking about professional computer work and corporate work environments, but I use a "Personal Computer" as a hobby. I've been out-of-industry for decades now. And when I say "Personal Computer" I'm not talking a hardware specification, rather I'm talking about "This is my personal computer where I do things my way, as opposed to my work computer where I do things my companies way". Dear listener, please remember that I did the first community show contribution to HPR, and my topic was about personalization. For me, a hobbyist interested in operating system experimentation, I don't want a system layer, I want a traditional unix-like system that operates on a two-layer model and does things my way, nobody else's way.

So, what advice can I give to those who don't want SystemD now? Well, recently I've left Debian. Debian, you see, supports init system diversity, but as you now know dear listener, that is different than being without SystemD. You may have heard that SystemD is linux-specific, that is to say that it runs only on linux, not anything like a BSD system or a Windows system. But you may be curious to know that it is also Gnu-libC specific. Which means that the C compiler must use GNU's libC standard library. Thus, if you have a system built around the Musl C standard library like Alpine or Void, or a system like Android that runs on the Bionic C Standard library, you wont have a SystemD system. I'm personally learning Void as its package manager supports both binary and a ports collection much like the BSD's. But that is what I'm doing on my personal computer, I leave you in the freedom to do things your way on your personal computer!