Does my system accept the new let's encrypt root certificate?

Question

Let's encrypt changes there root certificate from DST Root CA X3 to ISRG Root X1- how can I check if my server (which connects to an api with let's encrypt certificate) works still in future?

Answer 1

The let's encrypt certificate chain will be different in future, see here, here and here.

Problem may be older systems like ubuntu 16.04 without updates. If you want to be safe, just run this line to see if the new root certificate is installed:

awk -v cmd='openssl x509 -noout -subject' '
    /BEGIN/{close(cmd)};{print | cmd}' < /etc/ssl/certs/ca-certificates.crt | grep ISRG

As an idea by: List all available ssl ca certificates