Whilst it is possible to view the contents of an SSL cert from within most modern browsers I occasionally find the need to use the command line to find out the same information. I find this useful when renewing certificates as browsers can occasionally cache certificates for longer than expected, causing false results.
The following command connects to the server, downloads the SSL certificate from port 443 and then uses the openssl tool to extract the information from the certificate into a readable format.
echo | openssl s_client -showcerts -servername example.com -connect example.com:443 2>/dev/null | openssl x509 -inform pem -noout -text
This produces the following output.
Certificate: Data: Version: 3 (0x2) Serial Number: 0f:d0:78:dd:48:f1:a2:bd:4d:0f:2b:a9:6b:60:38:fe Signature Algorithm: sha256WithRSAEncryption Issuer: C=US, O=DigiCert Inc, CN=DigiCert SHA2 Secure Server CA Validity Not Before: Nov 28 00:00:00 2018 GMT Not After : Dec 2 12:00:00 2020 GMT Subject: C=US, ST=California, L=Los Angeles, O=Internet Corporation for Assigned Names and Numbers, OU=Technology, CN=www.example.org Subject Public Key Info: Public Key Algorithm: rsaEncryption Public-Key: (2048 bit) Modulus: 00:d0:f0:12:74:a0:96:20:72:08:65:19:12:5a:5d: 4a:d0:3a:8c:66:8f:a0:29:2b:a7:db:d5:ac:0c:cf: a5:71:92:15:42:15:b0:07:92:76:31:75:d7:27:8e: 4d:50:6a:75:d1:7b:53:5e:27:aa:ed:eb:a4:60:3a: f2:8e:45:18:6b:45:33:5c:85:11:aa:20:12:fe:60: ac:9d:4c:45:8f:dd:d3:0e:3e:77:0f:09:c2:85:65: 34:c7:22:fb:74:13:b9:42:9f:f7:21:f6:f0:9c:44: 74:6d:c9:df:b3:1f:8f:60:b7:71:11:06:90:63:41: 9d:8f:34:7b:24:49:46:ac:f2:f0:8d:0b:48:f4:d3: 92:1a:f7:a2:45:ee:cc:e5:d7:83:7f:2e:82:bd:71: dd:28:19:58:33:6e:11:a1:3a:a0:6a:72:60:92:01: 59:9f:63:17:7a:49:42:7b:9c:3f:db:d3:05:e8:cc: 87:7e:f8:aa:fc:9d:d1:05:50:ab:75:b1:1e:ba:20: cb:89:d4:6d:6c:37:82:28:4c:c5:3f:7c:c1:10:f5: a0:a5:66:6b:53:53:c9:db:ed:85:c3:6d:05:f8:64: a7:c9:0e:eb:8f:e1:c4:b1:eb:2d:68:0e:15:3f:e5: e2:dc:fc:21:64:2d:ee:69:2b:04:78:db:77:65:cb: 54:f9 Exponent: 65537 (0x10001) X509v3 extensions: X509v3 Authority Key Identifier: keyid:0F:80:61:1C:82:31:61:D5:2F:28:E7:8D:46:38:B4:2C:E1:C6:D9:E2 X509v3 Subject Key Identifier: 66:98:62:02:E0:09:91:A7:D9:E3:36:FB:76:C6:B0:BF:A1:6D:A7:BE X509v3 Subject Alternative Name: DNS:www.example.org, DNS:example.com, DNS:example.edu, DNS:example.net, DNS:example.org, DNS:www.example.com, DNS:www.example.edu, DNS:www.example.net X509v3 Key Usage: critical Digital Signature, Key Encipherment X509v3 Extended Key Usage: TLS Web Server Authentication, TLS Web Client Authentication X509v3 CRL Distribution Points: Full Name: URI:http://crl3.digicert.com/ssca-sha2-g6.crl Full Name: URI:http://crl4.digicert.com/ssca-sha2-g6.crl X509v3 Certificate Policies: Policy: 2.16.840.1.114412.1.1 CPS: https://www.digicert.com/CPS Policy: 2.23.140.1.2.2 Authority Information Access: OCSP - URI:http://ocsp.digicert.com CA Issuers - URI:http://cacerts.digicert.com/DigiCertSHA2SecureServerCA.crt X509v3 Basic Constraints: critical CA:FALSE 1.3.6.1.4.1.11129.2.4.2: ...k.i.w.......X......gp .....g\1.F.....H0F.!..d..!...H.v.K.F.W'..{.;.JWBl...l.!.....0.d..L|nXSW....EO..F..p...BB.v..u..Y|..C._..n.V.GV6.J.`....^......g\1.......G0E. o.w.....c-....A[email protected]/..f.._s.H.P..!....H.....D%.<...+.|..'{..X....JN.v.oSv.1.1.....Q..w.....}..c).-. MwZ.I.J.h..a... .1....q.C.....O...z....D;.... [.V.=,r. Signature Algorithm: sha256WithRSAEncryption 73:70:85:ef:40:41:a7:6a:43:d5:78:9c:7b:55:48:e6:bc:6b: 99:86:ba:fb:0d:03:8b:78:fe:11:f0:29:a0:0c:cd:69:14:0b: c6:04:78:b2:ce:f0:87:d5:01:9d:c4:59:7a:71:fe:f0:6e:9e: c1:a0:b0:91:2d:1f:ea:3d:55:c5:33:05:0c:cd:c1:35:18:b0: 6a:68:66:4c:bf:56:21:da:5b:d9:48:b9:8c:35:21:91:5d:dc: 75:d7:7a:46:2c:22:27:a6:6f:d3:3a:17:eb:be:bd:13:c5:12: 26:73:c0:5d:a3:35:89:6a:fb:27:d4:dd:aa:74:74:2e:37:e5: 01:3b:a6:d0:30:b0:83:d0:a1:c4:75:21:85:b2:e5:fa:67:00: 30:a2:bc:53:83:4d:bf:d6:a8:83:bb:bc:d6:ed:1c:b3:1e:f1: 58:03:82:00:8e:9c:ef:90:f2:1a:5f:a2:a3:06:da:5d:be:9f: da:5d:a6:e6:2f:de:58:80:18:d3:f1:62:7b:a6:a3:9f:ae:a8: 69:72:63:81:65:ae:82:83:a3:b5:97:8a:9b:20:51:ff:1a:3f: 61:40:1e:48:d0:6b:38:f9:e1:fa:17:d8:77:4a:88:e6:3d:36: 24:4f:ef:0a:b9:9f:70:f3:83:27:f8:cf:2a:05:75:10:a1:8a: 0a:80:88:cd