generating the TLS cert

[Robert Moskowitz]

I am looking at a number of tutorials for setup.  I have found two 
different commands and looking for guidance:

genkey --days 3650 mail.example.com
or

openssl req -new -outform PEM -out smtpd.cert -newkey rsa:2048 -nodes 
-keyout smtpd.key -keyform PEM -days 365 -x509

Now I actually know a LOT about X.509, having worked on PKIX in IETF.  
But I am theory, not practice.  I want control over CN content and the 
tutorial with the later shows what I want.