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systemd/README.md

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+### Systemd unit files for `step-ca`
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+For documetation 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).
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+For documentation on `cert-renewer@.*`, see [Automating Certificate Renewal](https://smallstep.com/docs/step-ca/certificate-authority-server-production#automate-x509-certificate-lifecycle-management)