If you can't login to a server via serial console and you got login: pam_securetty(login:auth): access denied: tty 'ttyS0' is not secure ! in logs then you have to add at the end of the file /etc/securetty the following lines:

# Standard serial ports
ttyS0
ttyS1

For production server I am using a securetty file which is attached to this page.

Files: securetty.zip