What is the function of the ACL mask during permission evaluation?

• A. It stores the file creation time
• B. It defines the maximum allowed permissions for ACL entries
• C. It lists all ACL entries
• D. It sets the sticky bit

Answer: (B)

ACL mask sets the upper bound for the permissions granted by named user and named group entries in a POSIX ACL. When access is evaluated, the effective rights for those entries are the lesser of what the specific entry allows and what the mask allows. This lets you constrain how much access ACLs can grant, independently from the file’s standard mode bits. The mask does not affect the owner’s permissions or the other bits like the sticky bit, and it doesn’t store timestamps or simply list entries—the mask’s role is to cap the maximum rights for the named entries.