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this post was submitted on 20 Aug 2023
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As someone who wrote an init system for fun and knows how udev and practically everything else associated with bringing a modern computer to a fully functional state (including network mounts, if that is your nitpick) works, i can not know what you are nitpicking about without you saying it. Not that someone who is actively supporting two commercial products to meet different requirements would have any idea what i am saying.
PS It's all simple really, just that it seems magic to people without curiosity.
Sure - it’s primarily the way systemd uses cgroups
For example, systemd’s use of cgroups for process monitoring makes it trivial to support setting resource limits for us
One of the major issues we’re having with systemd, and the reason we’re using OpenRC on a different project, is the way Before and After with targets still cause all the services to start at the same time, causing resource contention
An alternative we’ve used once is to create a special target for the services that had to start early, even if the entire boot took longer, and use a process to then request new targets be started by systemd
This project we found it simpler to use OpenRC, though
Calling them “functionally the same” without taking into account how process monitoring works on different init systems is disingenuous
Process monitoring, in the basic sense, is seeing if a process is running. You mean how they handle dependency trees/graphs ? From what i just read sysD targets are groups that can have other groups in them (aka inherit, aka "services", aka compose). I wonder if that is the core of the problem. Not that i care, that's the hole they dug for themselves when they insisted only pid EINS can orchestrate cgroups (didn't use to be).
Either way, in the overwhelming majority of use cases they are practically the same.
Bdw, i didn't downvote you. I reserve it only for the most irrational fans, aka parroting fanboys.
One of the big issues with process monitoring, in the general sense, is how PID 1 checks on processes
The cgroups usage lets them make use of a very powerful Linux-specific feature. Some competitors such as Upstart tried to use ptrace for this, but that causes services to run slower
“Is a process running” I think is a harder question than you realize. systemd also offers the ability to ask “is a process running correctly” through watchdogs, and “is a process using too much memory” or “is a process using too much CPU” and offer corrective action if they are
The systemd.target issues I mention are related to different design goals. Systemd tries to start as many services as possible at once, but we need some services up within 1 second, and the rest can take longer
One option I offered was a modification to systemd so that targets could handle Before/After during our design, but the maintenance of porting it over for each update versus using OpenRC was decided to be too much effort