Limit Times a User Can Use The Computer

If you have children or teenagers, you might want to limit the times of day that they can use the computer. Here is how I did it:

For this example, "sammy" is the username of the user to be limited.

To limit when the user can login, edit /etc/security/time.conf and add:
edit /etc/pam.d/common-account, add:
To force the user to logout at a specific time: run sudo crontab -e and in the editor add:
The user will be logged out at 9:00 pm.
There is a pretty good crontab turotial at http://ubuntuforums.org/showthread.php?t=102626
If you have not edited a crontab entry before, here is a tip: when you are done, press ctrl-o to save the file but don't change the filename (crontab will be looking for the filename given), then press ctrl-x to exit.

If you want to get fancy, you can give the user a warning notification:
sudo -u sammy crontab -e