You can edit the message-of-the-day file, /etc/motd, to include announcements or inquiries to all users of a system when they log in. Use this feature sparingly, and edit this file regularly to remove obsolete messages.
$ pfedit /etc/motd
Edit the text to include the message that will be displayed during user login. Include spaces, tabs, and carriage returns.
$ cat /etc/motd Welcome to the UNIX universe. Have a nice day.