Update certificates and OpenSSL on Ubuntu 14.04 and still getting expired LetsEncrypt certificate errors? [closed]
Solution 1:
There's no need to download all the ca certificates if you just wish to add one.
Simply download the new ISRG Root X1 root certificate in PEM format from Let's Encrypt's repository (having confirmed that the link is to the genuine HTTPS protected site of course).
Rename the file so that it's extension is .crt and place in /usr/local/share/ca-certificates.
Finally, run:
sudo update-ca-certificates --fresh