How to fix 'certificate, issued by ‘/C=US/O=Let's Encrypt/CN=R3’: Issued certificate has expired.'

How to fix 'certificate, issued by ‘/C=US/O=Let's Encrypt/CN=R3’:   Issued certificate has expired.'

This how-to has been tested on Ubuntu 14.xx and higher and may also work on some older Debian OS.

Step 1 - You have to update your operating system to latest minor version:

sudo apt-get update

sudo apt-get dist-upgrade

reboot

Step 2 - Comment out DST_Root_CA_X3.crt

nano /etc/ca-certificates.conf

find 'DST_Root_CA_X3.crt' then put an exclamation mark in front of the line, like this:

!mozilla/DST_Root_CA_X3.crt

Step 3 - Force Update Certificates

sudo update-ca-certificates --fresh

Step 4 - Retest

Your expired Root CA X3 certificate has now been updated!