UNIX file access is based on __________.

• A. GID or UID and UNIX permissions.
• B. GID or UID and ACLs.
• C. NT ACLs and SID.
• D. NT ACLs and UNIX permissions.

Answer: (A)

UNIX access is determined by who you are (the user’s UID) and what groups you belong to (the GID), in combination with the file’s permission bits. Each file has an owner and an owning group, and three sets of permissions—one for the owner, one for the group, and one for others—control what can be read, written, or executed. When access is requested, the system checks if the requester is the owner (then uses the owner permissions), else if the requester is in the owning group (then uses the group permissions), or otherwise uses the permissions for others. ACLs can extend this in some setups, but the foundational UNIX access relies on UID/GID and the UNIX mode bits.