tldr/pages/common/openssl-s_client.md

openssl s_client

Create TLS client connections. More information: https://docs.openssl.org/master/man1/openssl-s_client/.

• 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 < /dev/null s_client -connect {{host}}:{{port}}

• 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 < /dev/null s_client -connect {{host}}:443 -showcerts