Laurent Bercot:
Also, admittedly, I simply did not want to read the systemd unit file documentation to understand how to start a s6 supervision tree from systemd. I will do the effort and come up with a small unit file suitable for this.
* https://lists.debian.org/debian-user/2014/09/msg01715.html * http://jdebp.info./FGA/inittab-is-history.html * https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=752075#82