Useful site with SSL commands, CSR and certificate decoder:

Display certificate request

$ openssl req -noout -text -in /etc/apache2/ssl/server2016.csr

Display to whom it was issued from PEM file

$ openssl x509 -noout -in imapd.pem -subject

Display certificate

$ openssl x509 -noout -text -in /etc/apache2/ssl/server2016.crt

Create key

$ openssl genrsa 2048 >

Create certificate request from existing key (SHA2)

$ openssl req -new -key -sha256 -out server2016.csr

Create certificate request from existing certificate and key

$ openssl x509 -x509toreq -in -out

Show public key information

$ openssl rsa -in -pubout

Convert certificates to PEM format

$ openssl x509 -inform der -in linuxia.crt -out linuxia.pem

Test SSL connection and print out SSL certificate

$ openssl s_client -connect

Connect to SMTP server with STARTTLS

$ openssl s_client -connect --starttls smtp


For more information, check the OpenSSL Command-Line HOWTO.