==== Ubuntu 20.04 ====
  * 安裝 DNS CloudFlare Plugin<code sh>
apt install python3-certbot-dns-cloudflare
</code>
  * 建立 /root/lets-encrypt/cloudflare.ini <code sh>mkdir -p /root/lets-encrypt/</code>Exp:<file>
# Cloudflare API credentials used by Certbot
dns_cloudflare_email = cloudflare@example.com
dns_cloudflare_api_key = 0123456789abcdef0123456789abcdef01234567
</file>
  * 設定保護權限 <code sh>
chmod 600 /root/lets-encrypt/cloudflare.ini
</code>
  * 進行申請新憑證 Exp. example.com <code sh>
/usr/bin/certbot certonly \
  --dns-cloudflare \
  --dns-cloudflare-credentials /root/lets-encrypt/cloudflare.ini \
  --dns-cloudflare-propagation-seconds 10 \
  -d example.com
</code>
  * 進行定期更新憑證 Exp. example.com <code sh>
/usr/bin/certbot renew \
  --dns-cloudflare \
  --dns-cloudflare-credentials /root/lets-encrypt/cloudflare.ini \
  --dns-cloudflare-propagation-seconds 10
</code>
  * 設定每天自動檢查更新 
    - 建立 /root/lets-encrypt/renewcert.sh <code sh>
vi /root/lets-encrypt/renewcert.sh</code><file>
/usr/bin/certbot renew \
  --dns-cloudflare \
  --dns-cloudflare-credentials /root/lets-encrypt/cloudflare.ini \
  --dns-cloudflare-propagation-seconds 10
</file><code sh>
chmod a+x /root/lets-encrypt/renewcert.sh
</code>
    - 設定 /etc/crontab<code sh>
vi /etc/crontab</code><file>
:
# let's encrypt
35 2 * * * root /root/lets-encrypt/renewcert.sh > /tmp/renewcert.log
</file><code sh>
systemctl restart crond
</code>