Here’s a quick note for checking the contents of a TLS (SSL) server certificate with the OpenSSL command-line tools.
Comments: echo “Q” causes the openssl s_client to disconnect (quit) immediately after verifying connectivity. Replace your hostname and port for “your.fqdn.com:443”. The x509 command shows the contents of the certificate in text format.
This should return details for the server cert like: Issuer, Validity (Not Before, Not After), Subject (CN), Subject Alternative Name (SAN), etc. This is useful for verifying changes after installing a new cert or checking values for your existing certs (expiration, …).
Linux users will have openssl pre-installed. Windows users can find these tools in Git Bash, or with the latest Windows 10 in Windows Subsystem for Linux (WSL) distribution like Ubuntu.