Quick Answer
The answer is to set PasswordAuthentication no and use SSH keys, as disabling password authentication forces the use of key-based authentication, which is far more resistant to brute-force attacks than passwords. This works because SSH keys use asymmetric cryptography, where a private key remains on the client and a public key is stored on the server, making it computationally infeasible for an attacker to authenticate without possession of the private key. On the CompTIA Linux+ XK0-005 exam, this concept tests your understanding of the sshd_config directives, and a common trap is confusing PermitRootLogin no with PasswordAuthentication no—remember that disabling root login is a separate, complementary control that prevents direct root access, not password-based logins. A useful memory tip is “keys over passwords, root over sudo,” reinforcing that both settings together create layered defense.
This XK0-005 practice question tests your understanding of security. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 Linux administrator is hardening a server. Which TWO actions are effective in preventing unauthorized access via SSH? (Select TWO.)
Set PermitRootLogin yes
Why wrong: Allows root login.
Set PasswordAuthentication yes
Why wrong: Allows password authentication.
Disable the SSH service
Why wrong: Prevents all SSH access, which may be too restrictive.
Set PermitRootLogin no in /etc/ssh/sshd_config
Prevents direct root login.
Set PasswordAuthentication no and use SSH keys
Eliminates password-based attacks.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Set PermitRootLogin no in /etc/ssh/sshd_config
Option D is correct because setting `PermitRootLogin no` in `/etc/ssh/sshd_config` prevents direct root login via SSH, forcing administrators to log in as a regular user and then use `su` or `sudo` for privilege escalation. This reduces the attack surface by eliminating the ability to brute-force the root password directly over SSH.
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.
Set PermitRootLogin yes
Why it's wrong here
Allows root login.
Set PasswordAuthentication yes
Why it's wrong here
Allows password authentication.
Disable the SSH service
Why it's wrong here
Prevents all SSH access, which may be too restrictive.
Set PermitRootLogin no in /etc/ssh/sshd_config
Why this is correct
Prevents direct root login.
Related concept
Read the scenario before looking for a memorised answer.
Set PasswordAuthentication no and use SSH keys
Why this is correct
Eliminates password-based attacks.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
The trap here is that candidates may think disabling the SSH service (Option C) is a valid hardening step, but the question asks for actions that prevent unauthorized access *via SSH* while still allowing legitimate remote administration.
Detailed technical explanation
SSH key authentication uses asymmetric cryptography (RSA, ECDSA, or Ed25519) where the private key never leaves the client, making it resistant to password-guessing attacks. When `PasswordAuthentication no` is set, the SSH server will reject any password-based login attempt at the protocol level (SSH_MSG_USERAUTH_REQUEST with 'password' method), even before checking the user's password hash. In real-world scenarios, disabling root login and password auth together is a standard baseline in compliance frameworks like CIS Benchmarks for Linux.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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FAQ
Security — This question tests Security — Read the scenario before looking for a memorised answer..
The correct answer is: Set PermitRootLogin no in /etc/ssh/sshd_config — Option D is correct because setting `PermitRootLogin no` in `/etc/ssh/sshd_config` prevents direct root login via SSH, forcing administrators to log in as a regular user and then use `su` or `sudo` for privilege escalation. This reduces the attack surface by eliminating the ability to brute-force the root password directly over SSH.
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.
About these practice questions
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Same concept, more angles
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. An administrator needs to ensure that the SSH service only allows key-based authentication and disables password authentication. Which configuration file and directive should be modified?
mediumWhy D: Option D is correct because the SSH server configuration file is /etc/ssh/sshd_config, and setting 'PasswordAuthentication no' disables password-based logins, forcing key-based authentication. This directive must be set on the server side (sshd_config), not the client side (ssh_config), to enforce the policy for all incoming SSH connections.
Last reviewed: Jun 11, 2026
This XK0-005 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 XK0-005 exam.
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