The abbreviation "motd" stands for "message of the day", and this file has been traditionally used for exactly that (it requires much less disk space than mail to all users).
If you want to change this message in ubuntu server follow this procedure first you need to edit /etc/motd.tail file
sudo vi /etc/motd.tail
Enter your message save and exit the file
Now you can restart your ubuntu server to check your changes are working or not
For Ubuntu Intrepid Users
There is a new package that provides this functionality with more options, called update-motd, available in Ubuntu Universe for Intrepid.
Install update-motd in Ubuntu Intrepid
sudo aptitude install update-motd
This will complete the installation
This package seeks to make the /etc/motd (Message of the Day) more dynamic and valuable, by providing a simple, clean framework for defining scripts whose output will regularly be written to /etc/motd.
The update-motd package creates a directory, /etc/update-motd.d, and installs a cronjob, /etc/cron.d/update-motd, which calls /usr/sbin/update-motd every 10 minutes (by default).
/usr/sbin/update-motd uses run-parts to execute each script in /etc/update-motd.d in lexigraphic order, concatenating the results with the message-of-the-day header, /etc/motd.tail.
In this way, users, or even other packages can drop scripts into /etc/update-motd.d to affect the MOTD.
create a script, such as /etc/update-motd.d/10-stats
sudo vi /etc/update-motd.d/10-stats
add the following lines and save the file.
Make sure you chmod +x /etc/update-motd.d/10-stats.Then, you can either run /usr/bin/update-motd, or uptimeWait ~10 minutes and then log in.
This is very simple and great idea where you can see whatever information you want when you login in to your server.