This LPIC-2 practice question tests your understanding of file sharing and samba. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 Samba server is configured with 'security = ads' and joined to an Active Directory domain. Users can authenticate but cannot access shares. The smb.conf includes 'winbind use default domain = yes'. What could be the problem?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The 'valid users' parameter uses domain prefix while default domain is set
When 'winbind use default domain = yes' is set, Winbind strips the domain prefix from usernames, so users authenticate as 'username' instead of 'DOMAIN\username'. If the 'valid users' parameter in a share definition explicitly uses the domain prefix (e.g., 'valid users = DOMAIN\username'), the stripped username will not match, and access is denied. This mismatch is the most direct cause of authentication succeeding but share access failing.
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.
✗
The 'winbind use default domain' option should be 'no'
Why it's wrong here
Setting to no would require domain prefix, but the issue is mismatch.
✗
The 'idmap backend' is not configured
Why it's wrong here
idmap backend is for UID/GID mapping, not authentication.
✗
The Samba server's time is not synchronized with the domain controller
Why it's wrong here
Time sync affects Kerberos but not basic authentication.
✓
The 'valid users' parameter uses domain prefix while default domain is set
Why this is correct
If valid users expects 'DOMAIN\user' but winbind strips the domain, authentication fails.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates assume authentication success means all Samba operations are fine, overlooking the subtle interaction between 'winbind use default domain' and share-level access control parameters like 'valid users'.
Detailed technical explanation
How to think about this question
Under the hood, when 'winbind use default domain = yes' is active, Winbind's NSS module returns usernames without the domain component, and Samba's internal access control compares these stripped names against the 'valid users' list. If the list contains 'DOMAIN\user', the comparison fails because the incoming name is just 'user'. This is a common misconfiguration in mixed environments where some shares are defined with explicit domain prefixes and others rely on the default domain behavior. Real-world troubleshooting often involves checking the 'valid users' and 'invalid users' parameters in each share definition against the winbind default domain setting.
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 practitioner preparing for the LPIC-2 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
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.
File Sharing and Samba — This question tests File Sharing and Samba — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The 'valid users' parameter uses domain prefix while default domain is set — When 'winbind use default domain = yes' is set, Winbind strips the domain prefix from usernames, so users authenticate as 'username' instead of 'DOMAIN\username'. If the 'valid users' parameter in a share definition explicitly uses the domain prefix (e.g., 'valid users = DOMAIN\username'), the stripped username will not match, and access is denied. This mismatch is the most direct cause of authentication succeeding but share access failing.
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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