openssl x509 -enddate -noout -in /etc/letsencrypt/live/example.com/cert.pem

 openssl verify -CAfile certs/rootCA.crt certs/client.crt

 openssl verify -CAfile certs/rootCA.crt certs/server.crt

echo | openssl s_client -servername example.com -connect example.com:443 2>/dev/null | openssl x509 -noout -dates -issuer

 openssl rsa -in secret.key -text -noout | grep "Private-Key"

 openssl pkey -inform PEM -pubin -in pub.key -text -noout

 openssl x509 -in example.com.pem -text

 openssl s_client -starttls ftp -connect localhost:21

openssl s_client -connect example.com:443 -servername example.com:443 < /dev/null | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > public.crt

echo QUIT | openssl s_client -servername www.example.com:443 -connect xx.xxx.xxx.xx:443 -status 2> /dev/null | grep -A 17 'OCSP response:' | grep -B 17 'Next Update'

If you get an error like

Oct 23 17:55:05 hpb01-rp nginx[2837]: nginx: [emerg] SSL_CTX_use_PrivateKey_file("/etc/nginx/ssl/some.key") failed (SSL: error:0B080074:x509 certificate routines:X509_check_private_key:key values mismatch)

Check certificate and private key

openssl x509 -in /path/to/yourdomain.crt -noout -modulus | openssl sha1

openssl rsa -in /path/to/your.key -noout -modulus | openssl sha1

You need to get the same sha sum from both commands.

• https://www.xolphin.com/support/OpenSSL/Frequently_used_OpenSSL_Commands
• https://www.namecheap.com/support/knowledgebase/article.aspx/9781/2238/nginx-ssl-error0b080074x509-certificate-routines-x509checkprivatekeykey-values-mismatch