The maintainer script calls systemctl directly. Actions such as enabling
a unit file should be done using
deb-systemd-helper so that they work
on machines with or without systemd. Starting a service should be done via
invoke-rc.d if the service has a corresponding sysvinit script or
deb-systemd-invoke if it does not.
If you are using debhelper, please use the
addon, which is provided by
debhelper (>= 9.20160709~).