Certbot supports Ubuntu 12.04+ (14.04+ for the apache plugin), CentOS/RHEL 6+, and Debian 7+. With the exception of CentOS/RHEL 5 (which was released in 2007!),

Certbot supports Ubuntu 12.04+ (14.04+ for the apache plugin), CentOS/RHEL 6+, and Debian 7+. With the exception of CentOS/RHEL 5 (which was released in 2007!), all releases of those distributions that still receive security updates are supported. What OS are you referring to?