This book uses many different terms, some of which have the same meaning. We have listed some of these terms and their definitions here. The book also contains inline links to relevant Wikipedia articles.
- The policy is a system-wide set of rules enforced by grsecurity. A very good description is offered in the mandatory access control article: "Any operation by any subject on any object will be tested against the set of authorization rules (aka policy) to determine if the operation is allowed."
- access control list
- From a related Wikipedia article: "An access control list (ACL) is a list of permissions attached to an object. The list specifies who or what is allowed to access the object and what operations are allowed to be performed on the object." In the context of this book, an ACL is used to mean a single role or subject definition, or the whole policy file.
- Ruleset is used much in the same way as "access control list". It is perhaps more often used to refer to role or subject definitions than the whole policy file.
- An object is a part of the system that is used by the programs running on the system. It can be an absolute path to a file or a directory; a capability; a system resource; a PaX flag; network access (IP ACLs).
- A subject uses and accesses objects and the ruleset of the subject enforces what objects it may use and in what way. In practice a subject is most often a program running on the system. In grsecurity, a subject is defined as an absolute path to the actual program executable (e.g. /sbin/init) or a directory (e.g. /lib/hal/scripts).
- A role is an abstraction that encompasses traditional users and groups that exist in Linux distributions and special roles, that are specific to grsecurity. Roles can be used to split the responsibility of system administration into smaller logical sets of responsibilities, such as "database administrator" or "DNS administrator". Compare this approach to having a single superuser (e.g. root) that is used to do every administrative task on the system.
- With domains you can combine users that do not belong in the same group as well as groups so that they share a single policy. Domains work just like roles.