For documentation on `step-ca.service`, see [Running `step-ca` As A Daemon](https://smallstep.com/docs/step-ca/certificate-authority-server-production#running-step-ca-as-a-daemon).
See also: There is a systemd certificate renewal timer, in the [`systemd` directory of `smallstep/cli`](https://github.com/smallstep/cli/tree/master/systemd).