"systemctl" can run a "main" foreground process as follows:

    systemctl init apache2

---

Service templates are not fully supported. For example, the default
"postfix" instance on Debian is "postfix@-.service" and the following
workaround is required to start it by "systemctl" command:

  ln -sv /lib/systemd/system/postfix@.service /etc/systemd/system/postfix@-.service

See the following upstream bug report for details:

  https://github.com/gdraheim/docker-systemctl-replacement/issues/62
