How to display a message before login?
For local login (or telnet) you need to modify:
/etc/motd
For display a message before login you edit instead
/etc/issue
see http://www.cyberciti.biz/faq/howto-change-login-message/
For SSH, you need to change the Banner config option in sshd_config:
http://www.cyberciti.biz/tips/change-openssh-sshd-server-login-banner.html