Openssl s client -showcerts

openssl s_client -showcerts -connect YOUR_DOMAIN.COM:443
openssl s_client -showcerts -connect google.coom:443

openssl s_client -showcerts 

self signed certificate

openssl s_client -showcerts -connect google.com:443 
CONNECTED(00000006)
depth=0 OU = "No SNI provided; please fix your client.", CN = invalid2.invalid
verify error:num=18:self signed certificate
verify return:1 
depth=0 OU = "No SNI provided; please fix your client.", CN = invalid2.invalid
verify return:1 
write W BLOCK
--- 
Certificate chain
 0 s:/OU=No SNI provided; please fix your client./CN=invalid2.invalid
   i:/OU=No SNI provided; please fix your client./CN=invalid2.invalid
-----BEGIN CERTIFICATE-----
MIIDfDCCAmSgAwIBAgIJAJB2iRjpM5OgMA0GCSqGSIb3DQEBCwUAME4xMTAvBgNV
.../...

Errors

openssl s_client -showcerts -connect google.com
40D741D72F7F0000:error:8000006F:system library:BIO_connect:Connection refused:../crypto/bio/bio_sock2.c:114:calling connect()
40D741D72F7F0000:error:10000067:BIO routines:BIO_connect:connect error:../crypto/bio/bio_sock2.c:116:connect:errno=111

openssl s_client -showcerts  https://google.com
40B78119DD7F0000:error:10080002:BIO routines:BIO_lookup_ex:system lib:../crypto/bio/bio_addr.c:738:Servname not supported for ai_socktype connect:errno=0

See also

• openssl, openssl s_client
• TLS, mTLS: OpenSSL, LibreSSL, BoringSSL, WolfSSL, X.509, .pem, SNI, CT, OCSP, Mbed TLS, ALPN, your connection is not private, SSL Certificate Checker, Wildcard certificate, JA3 fingerprint, sslcan, TLS inspection