* http://manpages.ubuntu.com/manpages/wily/en/man5/systemd.ser...
* http://manpages.ubuntu.com/manpages/wily/en/man5/systemd.uni...
* https://wiki.ubuntu.com/SystemdForUpstartUsers
* http://askubuntu.com/questions/636899/
* http://askubuntu.com/a/613814/43344