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.
A systems administrator needs to restrict SSH access to a Linux server so that only users in the 'sshusers' group can log in. Which configuration change should be made in /etc/ssh/sshd_config?
Add 'AllowUsers sshusers'
Why wrong: AllowUsers restricts by user, not group.
Add 'DenyGroups all'
Why wrong: DenyGroups blocks groups, but does not explicitly allow sshusers.
Add 'AllowGroups sshusers'
AllowGroups restricts SSH access to members of the specified group.
Add 'PermitRootLogin no' and add users to sshusers
Why wrong: PermitRootLogin controls root access, not group-based access.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Add 'AllowGroups sshusers'
Option C is correct because the 'AllowGroups' directive in /etc/ssh/sshd_config restricts SSH login to only users who are members of the specified group. By adding 'AllowGroups sshusers', only users in the 'sshusers' group will be permitted to authenticate via SSH, while all others are denied. This is the standard OpenSSH mechanism for group-based access control.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Add 'AllowUsers sshusers'
Why it's wrong here
AllowUsers restricts by user, not group.
Add 'DenyGroups all'
Why it's wrong here
DenyGroups blocks groups, but does not explicitly allow sshusers.
Add 'AllowGroups sshusers'
Why this is correct
AllowGroups restricts SSH access to members of the specified group.
Related concept
Read the scenario before looking for a memorised answer.
Add 'PermitRootLogin no' and add users to sshusers
Why it's wrong here
PermitRootLogin controls root access, not group-based access.
Common exam traps
The trap here is that candidates confuse 'AllowUsers' with 'AllowGroups', mistakenly thinking that 'AllowUsers sshusers' would restrict access to members of the 'sshusers' group, when in fact it only allows a user whose exact username is 'sshusers'.
Detailed technical explanation
Under the hood, OpenSSH's 'AllowGroups' and 'DenyGroups' directives match against the user's supplementary group memberships as reported by the system's group database (e.g., /etc/group). The check occurs after authentication but before session creation, and if the user is not in any allowed group, the connection is rejected with 'Authentication refused' in the logs. In a real-world scenario, using 'AllowGroups' is preferred over 'AllowUsers' for scalability, as it avoids maintaining a long list of usernames and simplifies auditing via group membership.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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.
What to study next
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FAQ
Security — This question tests Security — Read the scenario before looking for a memorised answer..
The correct answer is: Add 'AllowGroups sshusers' — Option C is correct because the 'AllowGroups' directive in /etc/ssh/sshd_config restricts SSH login to only users who are members of the specified group. By adding 'AllowGroups sshusers', only users in the 'sshusers' group will be permitted to authenticate via SSH, while all others are denied. This is the standard OpenSSH mechanism for group-based access control.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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