I am a Linux user, but I don’t really know how most things work, even after years of casual use on my Main, I just started getting into Devuan and wondered then, what exacly does systemd do that most distros have it? What even is init freedom? And why should I care?
Systemd is the first program that runs once the kernel has started. It’s job is mostly just starting up other processes, and managing those other processes. If you don’t know what systemd is, then you probably shouldn’t care about if you’re using it or not, it’s good software but there are fine alternatives.
What makes systemd particularly interesting is that it is different from historical init systems. Historically these init systems were an unholy mess of shell scripts. This offers maximum flexibility, but limits the functionality of the init system itself. Systemd replaces these shell scripts with simple ini-like service files that allow everything to be declared simply and declaratively, and allows specifying more rich metadata, like dependencies. But it’s different, and some people place a higher value on “how it’s always been” than pragmatism. I personally have zero sympathy for them because throwing out objective progress to hold onto a broken system designed for 1960s computing is just dumb.
Preach.
Removed by mod
It’s especially funny because systemd isn’t one program any more than GNU is. It’s a project. systemd-initd handles init. systemd-journald handles journal logs. systemd-resolved handles DNS resolution. Etc. Each systemd daemon has one area of responsibility!
I mean to a certain degree, I can understand if people find a problem with Poetterings approach of doing things !CORRECTLY!. Like, systemd-resolved resolving A-records with multiple addresses ina deterministic fashion because it’s not defined not to be deterministic, and because actual load balancing would be better. It’s not wrong, but it’s breaking everything. And it got patched after some uproar. And there are a few things like that.
But at the same time - I don’t think people appreciate how hard doing process management right on linux can be, especially if the daemon to run is shitty. Like, init scripts just triggering the shutdown port on a tomcat - except the tomcat is stuck and not reacting to the normal shutdown port and now you have a zombie process and an init script in a fucked up state. Or, just killing the main process and for some reason not really removing the children, now there’s zombies all over the place. Or, not trying appropriate shutdown procedures first and just killing things, “because it’s easier” - except my day just got harder with a corrupt dataset. Or, just trying soft and “Pwease wexit Mr Pwocess” signals and then just giving up. Or having “start” just crash because there was a stale PID from an OOM killed process around. Man I’m getting anxiety just thinking about this.
And that’s just talking about ExecStart and ExecStop, pretty much, which I have done somewhat correct in a few init scripts back in the day (over months of iteration of edge cases). Now start thinking about the security features systemd-analyze can tell you about, like namespaces, unmapping syscalls, masking parts of the filesystem, … imagine doing that with the jankyness of the average init.d script. At that point I’d start thinking about rebooting systems instead of trying to restart services, honestly.
And similarly, I’m growing fond of things like systemd-networkd, systemd-timesyncd. I’ve had to try to manage NetworkManager automatically and jeez… Or just directly handling networking with network-scripts. Always a pleasure. Chucking a bunch of pretty readable ini-files into /etc/systemd/networkd is a blessing. They are even readable even to people rather faint on the networking heart.
I was with you until the last paragraph. Just about every init system is different from historical init systems. Do you really think OpenRC or runit or any of the other init systems people are using have any similarity to SysV init? I think you’re attacking a strawman in the last paragraph. (Edit: Except Slackware users. Slackware still does init the way it’s traditionally been done, but I can’t think of anyone else who does)
Yes? OpenRC is certainly much closer to sysvinit than systemd and in many ways just expands upon it.
I thought people hate systemd because it’s a resource hog compared to OpenRC. TIL i guess
The difference is absolutely negligible.
I never used openRC (outside of Docker containers that run Alpine) so I wouldn’t know. Linux community has enough controversies, init utils shouldn’t be one of them
Best answer I’ve ever read ☝🏻☺️
Solid answer.