"If you read my article “Get to know Linux: File
permissions” you know that it’s possible, out of the
box, to control who can access a file and what they can do with it.
This helps to make Linux a fairly secure system. But did you know
you can take even further control of that system with the help of
Access Control Lists? Access Control Lists allow you to provide
different levels of access to files and folders. Say, for instance,
user jlwallen creates a file but doesn’t want to allow anyone
to do anything with this file but he and another user, wookie (even
though there are other users that belong to the group jlwallen).
ACL can handle this task.
"In this article you will learn how to install and use ACL to
further enchance your file permissions on a Linux system."