How can systemd and systemctl be enabled and used in Ubuntu Docker containers? [closed]

This is by design. Docker should be running a process in the foreground in your container and it will be spawned as PID 1 within the container’s pid namespace. Docker is designed for process isolation, not for OS virtualization, so there are no other OS processes and daemons running inside the container (like systemd, cron, syslog, etc), only your entrypoint or command you run.

If they included systemd commands, you’d find a lot of things not working since your entrypoint replaces init. Systemd also makes use to cgroups which docker restricts inside of containers since the ability to change cgroups could allow a process to escape the container’s isolation. Without systemd running as init inside your container, there’s no daemon to process your start and stop commands.

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