this post was submitted on 25 Feb 2024
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Can containers boot on their own? Then they are hosts, if not they are guests.
Unless there is some kind of mutual 50/50 cohabitation of userspace with two different pid1s
pid 1 left pid 1 right
@cypherpunks @onlinepersona
It depends what you mean by "boot". Linux containers are by definition not running their own kernel, so Linux is never booting. They typically (though not always) have their own namespace for process IDs (among other things) and in some cases process ID 1 inside the container is actually another systemd (or another init system).
However, more often PID 1 is actually just the application being run in the container. In either case, people do sometimes refer to starting a container as "booting" it; I think this makes the most sense when PID 1 in the container is systemd as the word "boot" has more relevance in that scenario. However, even in that case, nobody (or at least almost nobody I've ever seen) calls containers "guests".
As to calling containers "hosts", I'd say it depends on if the container is in its own network namespace. For example, if you run
podman run --rm -it --network host debian:bookworm bashyou will have a container that is in the same network namespace as your host system, and it will thus have the same hostname. But if you omit--network hostfrom that command then it will be in its own network namespace, with a different IP address, behind NAT, and it will have a randomly generated hostname. I think it makes sense to refer to the latter kind of container as a separate host in some contexts.