1. Download latest code from GitHub.

        wget --no-check-certificate https://github.com/letsencrypt/letsencrypt/archive/master.zip

2. Decompress the package.

        unzip master.zip && rm master.zip

3. Go into Let's Encrypt directory.

        cd letsencrypt-master

4. Start request for SSL certificate using following command.

        ./letsencrypt-auto certonly --webroot -w /var/www/domain.com/ -d www.domain.com -d domain.com