XK0-006 Security Practice Question
An administrator needs to prevent a specific user 'bob' from logging in via SSH while allowing other users. Which configuration directive should be added to /etc/ssh/sshd_config?
⚠ Common exam trap
The trap is that candidates may choose AllowUsers with a whitelist (like option A) thinking it blocks bob, but it also blocks all other users not in the list. The question's requirement to 'prevent bob while allowing other users' is best met by a blacklist approach using DenyUsers. This tests understanding of whitelist vs. blacklist logic.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
DenyUsers bob
The DenyUsers directive in /etc/ssh/sshd_config explicitly blocks specific usernames from logging in via SSH. By specifying 'DenyUsers bob', only user bob is denied, while all other users remain allowed. This matches the requirement to prevent bob without affecting others. AllowUsers with a whitelist would also block bob but would require listing every other user, which is impractical and not the intended solution.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
AllowUsers alice charlie
Why it's wrong here
Incorrect. AllowUsers alice charlie would block bob, but it would also block all other users except alice and charlie, violating the requirement to allow other users.
- ✗
PermitRootLogin no
Why it's wrong here
Incorrect. PermitRootLogin controls root SSH access, not a specific user like bob.
- ✓
DenyUsers bob
Why this is correct
Correct. DenyUsers bob blocks only bob from SSH login, leaving all other users unaffected.
- ✗
AllowUsers bob
Why it's wrong here
Incorrect. AllowUsers bob would permit only bob and block everyone else, which is the opposite of the requirement.
Go deeper
Related to this question
Learn chapter
User and Group Administration
Key term
SSH
SSH (Secure Shell) is a cryptographic network protocol that provides secure, encrypted communication and remote administration between two devices over an unsecured network.
Key term
User
A user is any person, system, or device that interacts with an IT service, resource, or identity system, typically authenticated through credentials and authorized to perform specific actions.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This XK0-006 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the XK0-006 exam.