查看证书有效期
Let's Encrypt 默认情况下只提供三个月的有效期，在有效期剩余半个月的时候，Let's Encrypt 会发送邮件给你，提醒你需要做证书的续期操作。或者我们也可以通过以下命令查看证书的剩余有效期限：
$ ./certbot-auto certificates
Saving debug log to /var/log/letsencrypt/letsencrypt.log
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Found the following certs:
Certificate Name: example.com
Domains: *.example.com example.com
Expiry Date: 2019-06-19 09:37:01+00:00 (VALID: 89 days)
Certificate Path: /etc/letsencrypt/live/example.com/fullchain.pem
Private Key Path: /etc/letsencrypt/live/example.com/privkey.pem
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手动续期
如果你使用的是通配符域名，那么很不幸，你讲无法使用 certbot-auto renew 方法进行续期。我们可以尝试手动去续期，命令如下：
$ ./certbot-auto --server https://acme-v02.api.letsencrypt.org/directory \
-d "*.example.com" -d "example.com" \
--manual --preferred-challenges dns-01 certonly
已下部分是执行的日志
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator manual, Installer None
Cert is due for renewal, auto-renewing...
Renewing an existing certificate
Performing the following challenges:
dns-01 challenge for example.com
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NOTE: The IP of this machine will be publicly logged as having requested this
certificate. If you're running certbot in manual mode on a machine that is not
your server, please ensure you're okay with that.
Are you OK with your IP being logged?
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(Y)es/(N)o: Y
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Please deploy a DNS TXT record under the name
_acme-challenge.example.com with the following value:
mnDglnRF3P0VCEW6xoIDYblcswOJySkc3CPAQIwFm-c
Before continuing, verify the record is deployed.
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Press Enter to Continue
执行到这里时，我们就要开始添加记录了。打开你的域名提供商，添加一条TXT类型的记录。主机记录是上面打印出来的 _acme-challenge.example.com 记录值为 mnDglnRF3P0VCEW6xoIDYblcswOJySkc3CPAQIwFm-c。填写完毕之后，稍等一分钟，回车继续，不出意外的话，续期成功了。当然，你仍然需要重启 nginx。
Waiting for verification...
Cleaning up challenges
IMPORTANT NOTES:
- Congratulations! Your certificate and chain have been saved at:
/etc/letsencrypt/live/example.com/fullchain.pem
Your key file has been saved at:
/etc/letsencrypt/live/example.com/privkey.pem
Your cert will expire on 2019-06-19. To obtain a new or tweaked
version of this certificate in the future, simply run certbot-auto
again. To non-interactively renew *all* of your certificates, run
"certbot-auto renew"
- If you like Certbot, please consider supporting our work by:
Donating to ISRG / Let's Encrypt: https://letsencrypt.org/donate
Donating to EFF: https://eff.org/donate-le
