Use openssl to check SSL Certificate

Modern browsers provide the GUI to quickly check SSL certificate details

Sometimes in Linux environment, we need to use command line to check SSL certificate, then openssl comes to the picture.

$ echo | openssl s_client -servername NAME -connect HOST:PORT 2>/dev/null | openssl x509
$ echo | openssl s_client -servername NAME -connect HOST:PORT 2>/dev/null | openssl x509 -noout -${param}

• -text: print ssl certificate in text format, like echo | openssl s_client -connect www.google.com:443 2>/dev/null | openssl x509 -text
• -fingerprint: print certificate fingerprints
• -dates: print notBefor and notAfter date and time
• -subject: print subject name
• -issuer: print certificate issuer CA

Run man s_client to see the all available options.
Run man x509 to see the all available options.

Use below command to check ssl cert chain
openssl s_client -showcerts -connect example.com:443 -servername example.com