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 company has a Samba server configured as a domain member in an Active Directory domain. The server runs Samba 4.13. Recently, Windows clients have been unable to access shares, and the domain join seems broken. The administrator runs 'net ads testjoin' and gets 'Join to domain is not valid'. The smb.conf includes: security = ads, realm = EXAMPLE.COM, workgroup = EXAMPLE. The administrator can successfully resolve the domain controller via DNS. What should the administrator do to fix the issue?
Re-run 'net ads join -U administrator' to rejoin the domain.
This re-establishes the domain membership.
Restart the winbind service and run 'wbinfo -t'.
Why wrong: This tests trust, does not rejoin the domain.
Add 'kerberos method = secrets and keytab' to smb.conf.
Why wrong: This is the default, not a fix.
Increase the 'log level' to 3 and restart smbd.
Why wrong: This only increases logging, it does not fix the join.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Re-run 'net ads join -U administrator' to rejoin the domain.
The 'net ads testjoin' command returned 'Join to domain is not valid', which indicates the machine account password stored in the local secrets.tdb file no longer matches the one in Active Directory. Re-running 'net ads join -U administrator' re-establishes the secure channel by resetting the machine account password and updating the Kerberos keytab, restoring the domain membership.
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.
Re-run 'net ads join -U administrator' to rejoin the domain.
Why this is correct
This re-establishes the domain membership.
Related concept
Read the scenario before looking for a memorised answer.
Restart the winbind service and run 'wbinfo -t'.
Why it's wrong here
This tests trust, does not rejoin the domain.
Add 'kerberos method = secrets and keytab' to smb.conf.
Why it's wrong here
This is the default, not a fix.
Increase the 'log level' to 3 and restart smbd.
Why it's wrong here
This only increases logging, it does not fix the join.
Common exam traps
The trap here is that candidates often confuse a broken domain join with a simple service restart or trust test, but the 'Join to domain is not valid' error specifically indicates the machine account credentials are invalid and require a fresh join.
Detailed technical explanation
When a Samba server is a domain member, it maintains a machine account in Active Directory with a password that is automatically rotated every 30 days by default. If the local secrets.tdb or Kerberos keytab becomes out of sync (e.g., due to a backup restore or password mismatch), the secure channel fails. The 'net ads join' command re-authenticates with the domain controller using administrator credentials, resets the machine account password, and writes a new keytab, effectively re-establishing the trust.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
File Sharing and Samba — This question tests File Sharing and Samba — Read the scenario before looking for a memorised answer..
The correct answer is: Re-run 'net ads join -U administrator' to rejoin the domain. — The 'net ads testjoin' command returned 'Join to domain is not valid', which indicates the machine account password stored in the local secrets.tdb file no longer matches the one in Active Directory. Re-running 'net ads join -U administrator' re-establishes the secure channel by resetting the machine account password and updating the Kerberos keytab, restoring the domain membership.
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 25, 2026
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