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XK0-006 Practice Question: A user is trying to log in to a Linux server via…
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?
⚠ Common exam trap
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.
Answer choices
Why each option matters
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).
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.
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.
- ✗
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.
Go deeper
Related to this question
Learn chapter
Linux Fundamentals and History
Key term
User
A user is any person, system, or device that interacts with an IT service, resource, or identity system, typically authenticated through credentials and authorized to perform specific actions.
Key term
SSH
SSH (Secure Shell) is a cryptographic network protocol that provides secure, encrypted communication and remote administration between two devices over an unsecured network.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This XK0-006 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the XK0-006 exam.