LinuxSecurity.com: Implementing Access Control Lists using Linux

“Here’s information on implementing ACLs using Linux. Access
Control Lists (ACLs) support more fine-grained permissions.
Arbitrary users and groups can be granted or denied access in
addition to the three traditional classes of users. … The
main advantage of this mechanism is its simplicity. With just a
couple of bits, many permission scenarios can be modeled.
However, there often is a need to specify access permissions at a
more fine-grained level, especially for commercial applications and
their security requirements.”

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