$ sudo systemctl enable sddm
Synchronizing state for sddm.service with sysvinit using update-rc.d...
Executing /usr/sbin/update-rc.d sddm defaults
Executing /usr/sbin/update-rc.d sddm enable
Created symlink from /etc/systemd/system/display-manager.service to /lib/systemd/system/sddm.service.