To start a service at boot, use the enable command:

sudo systemctl enable application.service

This will create a symbolic link from the system’s copy of the service file (usually in /lib/systemd/system or /etc/systemd/system) into the location on disk where systemd looks for autostart files (usually /etc/systemd/system/some_target.target.wants).

update-rc.d service_name defaults

With sysv-rc-conf or sysvconfig

sysv-rc-conf service_name on