How to install SSL certificate for free ( Let's encrypt ) on Ubuntu 12.04 with Nginx only

https://www.sslforfree.com/

or

sudo wget https://dl.eff.org/certbot-auto 1

sudo mv certbot-auto /jet/etc/letsencrypt/certbot-auto

sudo chown root /jet/etc/letsencrypt/certbot-auto

sudo chmod 0755 /jet/etc/letsencrypt/certbot-auto

sudo chmod a+x /jet/etc/letsencrypt/certbot-auto

sudo /jet/etc/letsencrypt/certbot-auto --nginx --nginx-ctl /usr/sbin/nginx --nginx-server-root /etc/nginx

also can be helpful

update-ca-certificates