It is recommended that there should NOT be duplicate _______ in directories?

• A. Passwords
• B. Emails
• C. Usernames
• D. Groups

Answer: (C)

In a directory used for authentication, the username must be unique for every user. The username is the primary identifier the system uses to log in, apply permissions, and track activity. If two entries shared the same username, the directory wouldn’t know which account to authenticate or which set of permissions to apply, leading to security and access-control problems. Passwords aren’t required to be unique—they can be the same across users—so duplicating them isn’t a reliable way to identify someone. Emails and other attributes may or may not be unique depending on the setup, but the critical constraint that avoids identity clashes and ensures precise access control is that usernames are unique.