Getting to Know Linux File Permissions
At this point, you should now have a solid understand of the basic Linux file permissions. There are more advanced issues that you can now easily study, such as setuid and setgid and ACLs. Without a good foundation of the basics, however, you’d quickly get lost with those next-level topics.
Linux file permissions haven’t changed much, since the early days. And, they most likely won’t change much going into the future.