If you use Letsencrypt to create a free ssl for your site, you have to renew it about three months.
/opt/letsencrypt ./letsencrypt-auto renew
When run ./letsencrypt-auto renew command, you may encounter an error like this:
To solve this error, you can do following our tutorial.
Step 1. Run command below:
rm ./letsencrypt-auto* wget https://raw.githubusercontent.com/certbot/certbot/75499277be6699fd5a9b884837546391950a3ec9/letsencrypt-auto chmod +x ./letsencrypt-auto ./letsencrypt-auto --no-self-upgrade
Step 2. Run renew