Website: https://letsencrypt.org/

Let’s Encrypt is a new Certificate Authority: It’s free, automated, and open.

Certbot, previously the Let's Encrypt Client, is EFF's tool to obtain certs from Let's Encrypt, and (optionally) auto-enable HTTPS on your server. It can also act as a client for any other CA that uses the ACME protocol.

Certbot Official site: https://certbot.eff.org/
Get Certbot from: https://github.com/certbot/certbot

Install

CentOS 6

# sudo yum install epel-release
$ wget https://dl.eff.org/certbot-auto
$ chmod a+x certbot-auto

CentOS 7

# yum install epel-release
# yum install certbot

Cert

$ certbot[-auto] certonly
$ certbot[-auto] certonly --standalone -d example.com -d www.example.com

Renew

# certbot[-auto] renew [--dry-run] [--quiet]