service runs a System V init script in as predictable environment as possible, removing most environment variables and with current working directory set to /.

service works in most Linux distributions including Debian and Ubuntu.

systemd is the new system and service manager for Linux. It is a replacement for init system and can manage system startup and services. It starts up and supervises the entire system.

systemctl only works on systemd based Ubuntu like version 16.04 LTS and above.

systemd jobs start when they have to.

• [http://en.wikipedia.org/wiki/Systemd]
• [https://wiki.ubuntu.com/SystemdForUpstartUsers]

See init.

Upstart jobs start as soon as they can.