title: "tlsv1 alert unknown ca" error when using new SSL certificates
body: <p>I am configuring emqtt MQTT Broker with SSL/TLS certificates from Digicert. I had done the SSL configuration for the same broker some years back and it was fine. But when I configured the new broker installation with new certificates, I am getting &quot;unknown CA&quot; error.</p>
  <p>This is the SSL settings:</p>
  <pre><code>mqtt.listener.ssl.keyfile = etc/certs/prod.key 
  mqtt.listener.ssl.certfile = etc/certs/server.crt
  mqtt.listener.ssl.cacertfile = etc/certs/DigiCertCA.crt
  </code></pre>
  <p>And this is the error I saw in the server logs:</p>
  <pre><code>[error] &lt;0.27032.0&gt; SSL: certify: ssl_alert.erl:97:Fatal error: unknown ca
  </code></pre>
  <p>Can this be an issue with the new CA certifcate? Maybe it requires more dependent certificates in chain?</p>
  <p><strong>UPDATE</strong>
  This appears to be an OS issue.I got the following error when I tested the certificates using &quot;openssl verify&quot; in the server:</p>
  <pre><code>error 2 at 1 depth lookup:unable to get issuer certificate
  </code></pre>
  <p>Verify is success on my local PC with the same command and same certificates</p>
  <p>I updated the OS root certificates using &quot;yum update ca-certificates&quot;, but still I am getting the same error</p>