 Solution

An access control list is attached to an object, such as a file, and lists which subjects or groups may perform which operations. Access requires checking the requesting identity against that object's list. A security capability is an unforgeable reference to an object carrying specified rights; possessing valid authority is what permits access. Protected storage or another integrity mechanism must prevent users manufacturing stronger security capabilities.

The traditional Unix owner/group/other read-write-execute permissions are a compact, restricted access control list: the inode records the owner, group and permission bits, and the operating system compares these against the caller's credentials.An already-open file descriptor can behave like a limited handle carrying rights, but that does not change the identity-based nature of the initial pathname permission check.