See man psql.. Use the -servername switch to enable SNI in s_client. The handshake still passes OK because the extension appears to be non-essential (or at least considered to be such by openssl) and you get the connected TLS tunnel. openssl s_client -starttls smtp -connect example.com:25 openssl s_client -starttls smtp -connect example.com:465 openssl s_client -starttls smtp -connect example.com:587. openssl s_client-connect www. # openssl x509 -in cert.pem -out rootcert.crt. Let's break this down into two parts. Extract a certificate from a server. Making the HTTP request. For more information, see OpenSSL s_client commands man page in the OpenSSL toolkit. openssl s_client is not a particularly great tool for this, but it can be done. TLS/SSL and crypto library. # openssl s_client -connect server:443 -CAfile cert.pem. Don’t worry about this unless you need it because some application requires a PKCS12 file or you’re given one that you need to get stuff out of. To create a full circle, we’ll make sure our s_server is actually working by accessing it via openssl s_client: joris@beanie ~ $ openssl s_client -connect localhost:44330 CONNECTED(00000003) depth=0 C = NL, ST = Utrecht, L = Utrecht, O = Company, OU = Unit, CN = localhos t You didn't specify why you wanted to use s_client.. $ openssl s_client -connect www.feistyduck.com:443 -servername www.feistyduck.com In order to specify the server name, OpenSSL needs to use a feature of the newer handshake format (the feature is called Server Name Indication [SNI]), and that will force it to abandon the old format. openssl s_client -cipher ECDHE-RSA-AES256-SHA:ECDHE-RSA-AES256-GCM-SHA384 \ -connect example.com:443 The above list specifies two specific ciphers. As soon as you connect to the server, run: ehlo example.com. openssl s_client sni openssl s_client -connect example.com:443 -servername example.com. Hence in your test the openssl s_client command advertises that is supports NPN but the server turns a blind eye onto ot. Contribute to openssl/openssl development by creating an account on GitHub. Think of it like a zip file for keys & certificates, which includes options to password protect etc. You will get output like below as reply: To view a complete list of s_client commands in the command line, enter openssl -?. SNI is a TLS extension that supports one host or IP address to serve multiple hostnames so that host and IP no longer have to be one to one. If the connection succeeds then an HTTP command can be given such as "GET /" to retrieve a web page. The following table includes some commonly used s_client commands. A group of ciphers can also be passed. If it is to check the SSL certificate (which is why I came across your question), it still doesn't work with s_client as Magnus pointed out 7 years ago. 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