Official installation steps: https://certbot.eff.org/lets-encrypt/centosrhel7-nginx
How to install snapd on centos7: https://snapcraft.io/docs/installing-snap-on-fedora
Reference: https://blog.csdn.net/qq_37769323/article/details/104124108
如果centos的内核为：kernel 3.10.0-123.4.2.el7.x86_64 则会报错：error: system does not fully support snapd: cannot read the value of fs.may_detach_mounts kernel
parameter: open /proc/sys/fs/may_detach_mounts: no such file or directory
In this case, please upgrade your centos kernel. Reference: Note: You must execute yum update to update all packages before upgrading the kernel. Please refer to https://linux.cn/article-8310-1.html , otherwise the update will not succeed! [Refer to how to upgrade the Linux kernel: https://linux.cn/article-8310-1.html ]
The old installation method [timer automatic update is to use the command certbot -q renew ]: https://blog.csdn.net/weixin_43343144/article/details/108312285