The answer is only root, because the ACL mask set to r-- does not restrict the root user’s write permission. The mask defines the maximum effective permissions for named users and groups, but root operates outside the ACL model entirely, always retaining full read and write access regardless of mask settings. On the LPIC-2 exam, this concept tests your understanding that ACLs control discretionary access for regular users and groups, while root’s superuser privileges bypass all ACL and standard permission checks. A common trap is assuming the mask applies universally, but the key distinction is that root is never limited by ACL entries or masks. Remember the mnemonic: “Mask binds the named, but root remains untamed.”
LPIC-2 System Security Practice Question
This LPIC-2 practice question tests your understanding of system security. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Only root.
The correct answer is C because the ACL output shows that the mask is set to r--, which limits the effective permissions of named users and groups to read-only, regardless of their ACL entries. However, the root user is not subject to ACL restrictions and always has full access to any file, including write permission, making root the only user who can write to the file.
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.
✗
Only the user www-data.
Why it's wrong here
www-data has read-only permission.
✗
No one, because the mask is r--.
Why it's wrong here
Mask does not affect root's permissions.
✓
Only root.
Why this is correct
Root has rw- and is not limited by mask.
Related concept
Read the scenario before looking for a memorised answer.
✗
Any user in the www-data group.
Why it's wrong here
Group has r--.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often overlook that the ACL mask applies only to named users and groups, not to root, leading them to incorrectly believe that the mask r-- blocks all write access, including root's.
Detailed technical explanation
How to think about this question
The ACL mask defines the maximum permissions that can be granted to named users, named groups, and the owning group, but it does not affect the file owner or root. When a file has an ACL, the kernel applies the mask as a logical AND with the ACL entries for those subjects, effectively capping their effective permissions. This behavior is defined in POSIX 1003.1e draft standard and is critical in multi-user environments where fine-grained access control is needed without granting full permissions to all subjects.
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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
System Security — This question tests System Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Only root. — The correct answer is C because the ACL output shows that the mask is set to r--, which limits the effective permissions of named users and groups to read-only, regardless of their ACL entries. However, the root user is not subject to ACL restrictions and always has full access to any file, including write permission, making root the only user who can write to the file.
What should I do if I get this LPIC-2 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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Question Discussion
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