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Comment by moshmosh | Hacker News Reader

The nice thing about docker is that you can use the same tooling on lots of operating systems, not just that it wraps some Linux functionality. Sure, it may involve using a VM, depending on the system, but I still get to just run "docker" and "docker-compose" and such, as if it were native. A systemd solution would need a VM running Linux w/ systemd even on Linux, in some cases.

Really, though, if I care about isolation and don't want to use docker, I'm gonna reach for FreeBSD + jails anyway, and I don't think systemd's gonna change that for me any time soon. If I want containers with better tooling outside the target OS, I'll use docker. Systemd falls in an awkward middle that I don't have much interest in.

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> A systemd solution would need a VM running Linux w/ systemd even on Linux, in some cases.

But that's exactly what happens with docker anyway (e.g.: Docker is still running in the Linux VM when running it from a different operating system). And considering the widespread systemd adoption throughout the Linux ecosystem, it's far more likely for systemd to be already installed in the VM than docker anyway.

Docker on Linux runs in a VM? No.

Systemd docker-replacement on a non-systemd Linux would need to run in a VM, though.

Systemd-docker-replacement: works only on systemd-Linux. Tooling for any other arrangement, including non-systemd linux, left as an exercise to the user.

Docker: works on Linux—systemd or otherwise. Has tooling to making working on macOS or Windows non-terrible and lets you use (mostly) the same commands as you would on Linux.

I'm saying that cross-platform tooling is what makes Docker Docker. Systemd can't replace it without replacing the tooling, even if it can do the same thing only on systemd-Linux.

> Systemd docker-replacement on a non-systemd Linux would need to run in a VM, though.

Would it? There's no reason this hypothetical systemd-docker-replacement couldn't be architected in a way that would not have a runtime dependency on systemd-the-init-system.

In any case, I'm not even sure if systemd wants to be a docker replacement (although it does seem to pick up more and more container features lately). But there's definitely some overlap between the two projects (in particular around process/service management) but podman is a much more direct competitor to docker than systemd.

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