- A
AllowUsers alice charlie
By listing other users, bob is implicitly denied.
- B
PermitRootLogin no
Why wrong: This affects root only.
- C
DenyUsers bob
Why wrong: DenyUsers is a valid directive but not as common in exam context; AllowUsers is more typical.
- D
AllowUsers bob
Why wrong: This would allow bob, not deny him.
Question 109 of 1,000
XK0-005 Security Practice Question
This XK0-005 practice question tests your understanding of security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
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
✓
AllowUsers alice charlie
Option A is correct because the AllowUsers directive in /etc/ssh/sshd_config explicitly lists the usernames that are permitted to log in via SSH. By specifying 'AllowUsers alice charlie', only those users are allowed SSH access, effectively blocking user 'bob' without needing a DenyUsers directive. This directive is processed before authentication, so any user not in the list is immediately rejected.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 this is correct
By listing other users, bob is implicitly denied.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
PermitRootLogin no
Why it's wrong here
This affects root only.
- ✗
DenyUsers bob
Why it's wrong here
DenyUsers is a valid directive but not as common in exam context; AllowUsers is more typical.
- ✗
AllowUsers bob
Why it's wrong here
This would allow bob, not deny him.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often choose DenyUsers bob because it seems intuitive to block a specific user, but the question's requirement to 'prevent bob while allowing other users' is best met by AllowUsers with a whitelist, which is a common exam trick to test understanding of whitelist vs. blacklist logic.
Detailed technical explanation
How to think about this question
The AllowUsers and DenyUsers directives are processed by sshd during the authentication phase, before password or key verification. AllowUsers supports patterns and can include user@host syntax for finer control. In a real-world scenario, using AllowUsers with a whitelist is often preferred for security hardening because it defaults to denying all unspecified users, reducing the attack surface compared to a DenyUsers blacklist approach.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
Visual reference
What to study next
Got this wrong? Here's your next step.
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FAQ
Questions learners often ask
What does this XK0-005 question test?
Security — This question tests Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: AllowUsers alice charlie — Option A is correct because the AllowUsers directive in /etc/ssh/sshd_config explicitly lists the usernames that are permitted to log in via SSH. By specifying 'AllowUsers alice charlie', only those users are allowed SSH access, effectively blocking user 'bob' without needing a DenyUsers directive. This directive is processed before authentication, so any user not in the list is immediately rejected.
What should I do if I get this XK0-005 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
This XK0-005 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 XK0-005 exam.
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