Compatibility Between the Superuser and Privilege Models

To accommodate legacy applications, the implementation of privileges works with both the superuser and privilege models. This accommodation is achieved through use of the PRIV_AWARE flag, which indicates that a program works with privileges. The PRIV_AWARE flag is handled automatically by the operating system.

Consider a child process that is not aware of privileges. The PRIV_AWARE flag for that process would be false. Any privileges that have been inherited from the parent process are available in the permitted and effective sets. If the child sets a UID to 0, the process's effective and permitted sets are restricted to those privileges in the limit set. The child process does not gain full superuser powers. Thus, the limit set of a privilege-aware process restricts the superuser privileges of any non-privilege-aware child processes. If the child process modifies any privilege set, then the PRIV_AWARE flag is set to true.