Quick Answer
The answer is disabling unnecessary services. This is a core best practice for securing a Linux server because every running service represents a potential entry point for an attacker; by removing or stopping services like Telnet, FTP, or unused web servers, you directly reduce the attack surface and eliminate unneeded daemons that could be exploited. On the CompTIA Linux+ XK0-005 exam, this concept tests your understanding of the principle of least functionality, often appearing alongside questions about managing systemd units or using tools like `systemctl list-units` to audit running services. A common trap is confusing disabling a service with simply stopping it temporarily—remember that disabling ensures the service does not start on boot, while stopping only halts it for the current session. For a quick memory tip, think “disable, don’t just stop” to lock in the permanent security posture.
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.
Which THREE are best practices for securing a Linux server? (Choose exactly three.)
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "best"
Why it matters: Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Use a host-based firewall
Controls network access to the server.
Keep software up to date
Patches vulnerabilities.
Enable root SSH login with password
Why wrong: Root SSH login with password is insecure; it should be disabled or use key-only.
Disable unnecessary services
Reduces attack surface.
Set default umask to 0777
Why wrong: umask 0777 results in insecure permissions (000 for new files), it should be restrictive like 0022.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Use a host-based firewall
A host-based firewall (e.g., iptables, nftables, or firewalld) controls incoming and outgoing traffic at the server level, enforcing least-privilege network access. By default, it can block all traffic except explicitly allowed services (e.g., SSH on port 22, HTTPS on port 443), reducing the attack surface. This is a fundamental security control to prevent unauthorized network connections.
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.
Use a host-based firewall
Why this is correct
Controls network access to the server.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Keep software up to date
Why this is correct
Patches vulnerabilities.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Enable root SSH login with password
Why it's wrong here
Root SSH login with password is insecure; it should be disabled or use key-only.
Disable unnecessary services
Why this is correct
Reduces attack surface.
Clue confirmation
The clue word "best" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Set default umask to 0777
Why it's wrong here
umask 0777 results in insecure permissions (000 for new files), it should be restrictive like 0022.
Common exam traps
CompTIA often tests the misconception that a permissive umask (like 0777) is secure because it 'blocks everything,' but in reality, umask subtracts permissions, so 0777 actually removes all permissions, which is not a best practice and can cause operational issues; the trap is confusing umask subtraction with direct permission setting.
Detailed technical explanation
Under the hood, umask is a bitmask that subtracts permissions from the base permissions (666 for files, 777 for directories). A umask of 0777 results in files with 000 (no permissions) and directories with 000, which may break system functionality, but more critically, it reflects a misunderstanding of umask logic. In real-world scenarios, a misconfigured umask can lead to privilege escalation or data exposure, especially in shared hosting environments where multiple users access the same filesystem.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A junior network technician can log in to a core router but cannot reach the enable prompt or configuration mode. The AAA server is authenticating the login — but the authorisation policy only grants privilege level 1, not 15. Authentication (who you are) is working; authorisation (what you can do) is not.
What to study next
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Security — study guide chapter
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FAQ
Security — This question tests Security — Read the scenario before looking for a memorised answer..
The correct answer is: Use a host-based firewall — A host-based firewall (e.g., iptables, nftables, or firewalld) controls incoming and outgoing traffic at the server level, enforcing least-privilege network access. By default, it can block all traffic except explicitly allowed services (e.g., SSH on port 22, HTTPS on port 443), reducing the attack surface. This is a fundamental security control to prevent unauthorized network connections.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "best". Signals that multiple options may be partially correct. Choose the option that most directly solves the exact problem described, not the one that sounds most complete.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 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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