openssl s_client

OpenSSL command to create TLS client connections. More information: https://www.openssl.org/docs/manmaster/man1/openssl-s_client.html.

• Display the start and expiry dates for a domain’s certificate:

openssl s_client -connect host:port 2>/dev/null | openssl x509 -noout -dates

• Display the certificate presented by an SSL/TLS server:

openssl s_client -connect host:port </dev/null

• Set the Server Name Indicator (SNI) when connecting to the SSL/TLS server:

openssl s_client -connect host:port -servername hostname

• Display the complete certificate chain of an HTTPS server:

openssl s_client -connect host:443 -showcerts </dev/null