Quick Answer
The correct command is `chmod 600 /etc/shadow`, which sets read and write permissions exclusively for the root owner while stripping all access from group and others. This is essential because the /etc/shadow file stores hashed user passwords, and permissions 777 would allow any user on the system to read, modify, or even execute the file, creating a critical security vulnerability that exposes password hashes to brute-force attacks. On the CompTIA Linux+ XK0-005 exam, this scenario tests your understanding of Linux file permissions and the principle of least privilege, often appearing as a straightforward fix for a security audit finding. A common trap is confusing this with `chmod 644`, which would still allow group or others to read the file—remember, shadow must be root-only. A useful memory tip: think of "600" as "six-zero-zero" meaning "only the owner (root) gets the key (read/write), and everyone else gets zero access."
This XK0-005 practice question tests your understanding of security. 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 security audit reveals that the /etc/shadow file has permissions 777. Which command should be used to correct this vulnerability?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "which command"
Why it matters: Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
chmod 660 /etc/shadow
Why wrong: Allows group write, which is insecure.
chmod 600 /etc/shadow
Only root can read/write.
chmod 644 /etc/shadow
Why wrong: Allows world read, which is insecure.
chmod 640 /etc/shadow
Why wrong: Allows group read, which is insecure.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
chmod 600 /etc/shadow
The /etc/shadow file stores hashed user passwords and must be readable only by root to prevent unauthorized access. Permissions 777 allow any user to read, write, and execute the file, which is a critical security vulnerability. The correct command is `chmod 600 /etc/shadow`, which sets read and write permissions for the owner (root) only, denying all access to group and others.
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.
chmod 660 /etc/shadow
Why it's wrong here
Allows group write, which is insecure.
chmod 600 /etc/shadow
Why this is correct
Only root can read/write.
Clue confirmation
The clue word "which command" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
chmod 644 /etc/shadow
Why it's wrong here
Allows world read, which is insecure.
chmod 640 /etc/shadow
Why it's wrong here
Allows group read, which is insecure.
Common exam traps
The trap here is that candidates often confuse the required permissions for /etc/shadow with those for /etc/passwd (which is 644), leading them to choose 644 or 640 instead of the more restrictive 600.
Detailed technical explanation
The /etc/shadow file is owned by root and typically has group 'shadow' on many Linux distributions, but the standard secure permission is 600 (or 640 only if specific daemons like unix_chkpwd need group read). The execute bit on a regular file is meaningless here, but 777 would allow any user to execute the file as a script, potentially leading to privilege escalation if the file contains executable content. In practice, many security benchmarks (e.g., CIS) mandate 600 for /etc/shadow.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A security administrator must allow nursing staff to reach a patient records server while blocking access from the guest Wi-Fi VLAN. After applying an extended ACL, traffic is still blocked from nursing workstations. The ACL was applied outbound instead of inbound on the wrong interface. Questions like this test ACL direction and placement rules.
What to study next
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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: chmod 600 /etc/shadow — The /etc/shadow file stores hashed user passwords and must be readable only by root to prevent unauthorized access. Permissions 777 allow any user to read, write, and execute the file, which is a critical security vulnerability. The correct command is `chmod 600 /etc/shadow`, which sets read and write permissions for the owner (root) only, denying all access to group and others.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "which command". Tests specific CLI syntax. Recall the exact command and its required context — near-synonyms and partial matches are common distractors.
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. A security audit reveals that a server's /etc/shadow file is readable by all users. Which command would correctly fix the permissions?
hardWhy B: Option A is correct because 'chmod 600 /etc/shadow' sets the file to be readable and writable only by the owner (root), which is the standard permission. Option B (640) allows group read access. Option C (644) allows world read. Option D includes a chown that is unnecessary.
Last reviewed: Jun 11, 2026
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