Which utility is used to modify Access Control List entries on Linux files?

• A. chmod
• B. setfacl
• C. chown
• D. ls

Answer: (B)

Access Control Lists extend the traditional permission model by letting you grant or restrict access for additional users and groups beyond the owner, group, and others. To modify these ACL entries, you use setfacl. It writes or updates entries, such as giving a specific user read and write rights with a command like setfacl -m u:alice:rw- filename. You can also remove entries or set default ACLs on directories. The basic chmod operation only changes the standard owner/group/other bits and does not touch ACLs, while chown changes who owns the file and ls merely shows permissions (ACLs are shown if the system is configured to display them).