Let’s Encrypt的证书自然不用多说，大家都知道是一个免费的SSL证书，对于个人及小企业来说，Let’s Encrypt家的证书绝对是够用了。
虽然Let’s Encrypt家的证书是个好东西，但是申请的方式却千差万别，我这里提供一种差异化的申请方式，在Debian、CentOS、Ubuntu系统上能做到无差异的进行部署Let’s Encrypt家的SSL证书。
下载及给certbot赋予可执行权限
首先，选择需要保存certbot文件的目录，可以自定义，也可以选择现有目录，我是选择现有的系统目录，路径是/usr/local/src，先进入保存目录：
cd /usr/local/src
用wget命令下载certbot：
wget https://dl.eff.org/certbot-auto
再赋予可执行权限：
chmod +x certbot-auto
到这里，certbot程序就算安装好了，我们接下来就可以使用certbot程序进行证书申请了。
利用certbot申请Let’s Encrypt证书
利用certbot申请Let’s Encrypt证书需要如下几个条件：
– 系统的root权限
– 443端口未被占用，防火墙放行443端口，且外网能直接访问本机的443端口
– 域名解析到了当前主机
满足以上条件之后，我们就能开始进行Let’s Encrypt证书的申请了。
执行如下命令，我们可在交互程序中进行申请SSL证书：
./certbot-auto certonly
第一次执行的时候，可能会进行一些初始化、安装所必须的依赖等操作，期间可能需要手动确认，待安装完成之后，会要求输入一些所需要的信息，步骤如下：
root@BWH123:/usr/local/src# ./certbot-auto certonly
Bootstrapping dependencies for Debian-based OSes... (you can skip this with --no-bootstrap)
... #略过其中一些系统依赖安装步骤
How would you like to authenticate with the ACME CA?
-------------------------------------------------------------------------------
1: Spin up a temporary webserver (standalone)
2: Place files in webroot directory (webroot)
-------------------------------------------------------------------------------
Select the appropriate number [1-2] then [enter] (press 'c' to cancel): 1 #选择认证方式，建议选择1
Plugins selected: Authenticator standalone, Installer None
Enter email address (used for urgent renewal and security notices) (Enter 'c' to
cancel): bwh321@live.com #输入想使用的邮箱，用于接收证书到期提醒等信息，建议选择常用的
-------------------------------------------------------------------------------
Please read the Terms of Service at
https://letsencrypt.org/documents/LE-SA-v1.2-November-15-2017.pdf. You must
agree in order to register with the ACME server at
https://acme-v01.api.letsencrypt.org/directory
-------------------------------------------------------------------------------
(A)gree/(C)ancel: A # 同意TOS，输入A
-------------------------------------------------------------------------------
Would you be willing to share your email address with the Electronic Frontier
Foundation, a founding partner of the Let's Encrypt project and the non-profit
organization that develops Certbot? We'd like to send you email about EFF and
our work to encrypt the web, protect its users and defend digital rights.
-------------------------------------------------------------------------------
(Y)es/(N)o: N # 是否愿意共享邮箱给EFF，我选择了N
Please enter in your domain name(s) (comma and/or space separated) (Enter 'c'
to cancel): ssl.bwh123.com #输入需要申请的域名
Obtaining a new certificate
Performing the following challenges:
http-01 challenge for ssl.bwh123.com
Waiting for verification...
Cleaning up challenges
IMPORTANT NOTES:
- Congratulations! Your certificate and chain have been saved at:
/etc/letsencrypt/live/ssl.bwh123.com/fullchain.pem
Your key file has been saved at:
/etc/letsencrypt/live/ssl.bwh123.com/privkey.pem
Your cert will expire on 2018-05-28. 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"
- Your account credentials have been saved in your Certbot
configuration directory at /etc/letsencrypt. You should make a
secure backup of this folder now. This configuration directory will
also contain certificates and private keys obtained by Certbot so
making regular backups of this folder is ideal.
- 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
root@BWH123:/usr/local/src#
可以看到，按照要求输入之后，我们成功申请了Let’s Encrypt的证书，其中证书路径在/etc/letsencrypt/live/ssl.bwh123.com，需要搭配Nginx或者Apache使用的话，直接使用就好了。
证书快到有效期结束时，我们同样也可以使用这个小程序来进行证书有消息更新，更新命令为：
./certbot-auto renew
查看帮助信息可以使用如下命令：
./certbot-auto –help
本命令在Vultr及BandwagonHost及DigitalOcean及Linode上的VPS测试通过，搭配Nginx之后可以正常使用，至于SSL证书的情况，可以查看本站的SSL证书，用的就是Let’s Encrypt的证书。
参考信息：https://certbot.eff.org/#pip-other