openssl x509 -enddate -noout -in /etc/letsencrypt/live/example.com/cert.pem

 openssl verify -CAfile certs/rootCA.crt certs/client.crt

 openssl verify -CAfile certs/rootCA.crt certs/server.crt

 echo | openssl s_client -servername example.com -connect example.com:443 2>/dev/null | openssl x509 -noout -dates -issuer

 openssl rsa -in secret.key -text -noout | grep "Private-Key"

 openssl pkey -inform PEM -pubin -in pub.key -text -noout

 openssl x509 -in example.com.pem -text

 openssl s_client -starttls ftp -connect localhost:21