My religious view, having started since the Slackware on CD days with original rc and experienced upstart, launchd, openrc, daemontools, runit, daemontools-encore and s6 is: SystemD does too much, has too many dependencies, does it awkwardly and is unfriendly to configuration management, robustness, troubleshooting, "least surprise" principle and simplicity.
If I were Debian devs, there are two choices to init-agnosticism: a) pick one init provider at a time or b) manage multiple init systems simultaneously. For the latter, a very simple meta-init process could either exec() the only init system if one is used or supervise 2+ init systems. Then, there would need to be a tool to manage the lifecycle of a service no matter which init system it belonged to.
It might be easier to pick a), but a common use-case is to use daemontools for custom or other services that need to be kept running. Granted, there are probably packages that already run daemontools, runit or daemontools-encore as a child under the existing system init.
It's times like these that I wish there were a capabilities-oriented standard file layout such that every service knew how to start, soft-stop, hard-stop, enable, disable, reload-config and validate-config itself rather than every N init system having to find magic command-line args to not spawn in the background, change the user/group and change the log level, ports, bound address(es) and log destination. And then Cfengine, augeas, puppet, chef, salt, etc. reimplemented all of that logic per service. Services should also know how to backup/restore/wipe their own data (if not a 12Factor service themselves), whether they're up/down and how to gather their own metrics... and then cacti, nagios, nrpe and so on implemented all of that sort of logic per service too. sigh Cross-cutting concerns should be managed at the place that knows best how to manage the data and process lifecycle best: per service. Then, once that's done in a standard way, /etc configuration and configuration management can customize away. Having each service become enumerable and discoverable like a Bluetooth profile is another matter.
Experimenting with FreeBSD has been a breath of fresh air. Things I've come to expect to take an extended amount of time figuring out just work out of the box.
Some systemd advocates say the critics are just upset at change. I don't dislike change in general, but changing defaults out from under me? Defaults like this? That irks me. I lost a several tmux sessions before I realized what was happening. I thought I was doing something wrong because SystemD violated my expectations so severely.
The whole point is for the administrators to be able to avoid users running long-running processes on shared systems (e.g. university systems).
Of course not. But I do want to have the nohup software they have running to keep running when they log out.
> The whole point is for the administrators to be able to avoid users running long-running processes on shared systems (e.g. university systems).
Right, which is why it should be possible to do this. The issue is that the default behavior has changed from honoring nohup to not honoring nohup. Defaulting to honoring nohup is what's expected, and is reasonable.