The answer is the user's home directory having incorrect permissions, such as being group-writable, because SSH’s StrictModes setting (enabled by default) performs a security check on the home directory itself, not just the authorized_keys file. Even when ~/.ssh/authorized_keys has proper 600 permissions and correct ownership, StrictModes will reject the key if the home directory is group-writable or world-writable, as this could allow other group members to alter the directory’s contents and compromise authentication. On the CompTIA Linux+ XK0-005 exam, this scenario tests your understanding of SSH permission denied due to home directory permissions, a common trap where candidates focus only on file permissions and overlook the directory. The exam often pairs this with PubkeyAuthentication and PasswordAuthentication settings to mislead you. A solid memory tip: “Home writable, SSH disabled”—if the home directory is writable by anyone other than the owner, StrictModes blocks the key.
XK0-005 Troubleshooting Practice Question
This XK0-005 practice question tests your understanding of troubleshooting. 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.
A user is trying to log in to a Linux server via SSH but receives 'Permission denied (publickey,gssapi-keyex,gssapi-with-mic)'. The user's public key is in ~/.ssh/authorized_keys with proper permissions (600) and owned by the user. The server's sshd_config has 'PubkeyAuthentication yes' and 'PasswordAuthentication no'. What is the most likely additional cause?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "most likely"
Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The user's home directory has incorrect permissions (e.g., group-writable).
Option B is correct because SSH server's `StrictModes` (enabled by default) checks that the user's home directory is not group-writable or world-writable. If the home directory has group-write permission (e.g., 775), SSH refuses to trust `~/.ssh/authorized_keys` even if the file itself has 600 permissions. This is a security measure to prevent other group members from modifying the authorized_keys file indirectly.
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 server's firewall is blocking port 22.
Why it's wrong here
Firewall block would result in 'Connection refused' or timeout, not 'Permission denied'.
✓
The user's home directory has incorrect permissions (e.g., group-writable).
Why this is correct
SSH enforces strict permissions on home directory; if group-writable, the key authentication is refused.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
✗
SELinux is blocking the key authentication.
Why it's wrong here
SELinux would typically cause AVC denials, not 'Permission denied' specifically on key authentication.
✗
The SSH server is not running.
Why it's wrong here
If SSH server were not running, the connection would be refused entirely.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the subtlety that SSH's `StrictModes` checks parent directory permissions, not just the key file, leading candidates to overlook home directory permissions when the key file itself appears correct.
Detailed technical explanation
How to think about this question
Under the hood, `sshd` performs a series of permission checks before accepting a public key: the home directory must not be writable by group or others (mode 755 or stricter), `~/.ssh` must be 700, and `authorized_keys` must be 600. This behavior is controlled by the `StrictModes` directive in `sshd_config` (default yes). A real-world scenario is when a user's home directory is accidentally set to 775 by a backup script or admin, causing all key-based logins to fail silently.
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 XK0-005 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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this XK0-005 question in full detail.
Troubleshooting — This question tests Troubleshooting — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The user's home directory has incorrect permissions (e.g., group-writable). — Option B is correct because SSH server's `StrictModes` (enabled by default) checks that the user's home directory is not group-writable or world-writable. If the home directory has group-write permission (e.g., 775), SSH refuses to trust `~/.ssh/authorized_keys` even if the file itself has 600 permissions. This is a security measure to prevent other group members from modifying the authorized_keys file indirectly.
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.
Are there clue words in this question I should notice?
Yes — watch for: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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