当执行：

sudo snap install --classic certbot

报错：

error: cannot install "certbot": Post
       "https://api.snapcraft.io/v2/snaps/refresh": x509: certificate signed by
       unknown authority

方法：

yum -y install ca-certificates

然鹅依然无效。

参考：https://blog.csdn.net/xiunai78/article/details/104967014

系统更新：

yum update -y --nogpgcheck