The answer is `chmod 640 /etc/shadow; chattr +i /etc/shadow`. This is correct because `chmod 640` sets the file permissions to read/write for the root owner and read-only for the shadow group, while stripping all access from others—directly fixing the insecure 0644 permissions that allowed any local user to read password hashes. The `chattr +i` command then sets the immutable attribute, which prevents any accidental or unauthorized modification, deletion, or renaming of the file, even by root, until the attribute is explicitly removed. On the CompTIA Linux+ XK0-005 exam, this scenario tests your understanding of both standard Linux file permissions and the `chattr` command for advanced file security; a common trap is forgetting that `chmod 640` alone does not protect against root-level changes or accidental overwrites, so the immutable flag is essential for full compliance. Remember the mnemonic: "640 locks the door, +i bolts it shut."
XK0-005 Security Practice Question
This XK0-005 practice question tests your understanding of security. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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 0644 and is owned by root:shadow. The auditor states that this is a security risk because any local user can read password hashes. The administrator wants to fix the permissions to ensure that only root and the shadow group can read the file, and no one else can read it. Additionally, the administrator wants to set the immutable attribute on the file to prevent accidental modification. Which set of commands achieves the desired state?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
chmod 640 /etc/shadow; chattr +i /etc/shadow
Option A is correct because chmod 640 sets the file permissions to read/write for root (owner) and read-only for the shadow group, while removing all access for others. chattr +i sets the immutable attribute, which prevents any modifications (including deletion, renaming, or content changes) even by root until the attribute is removed. This satisfies the requirement that only root and the shadow group can read the file, and no one else can read it, while also protecting against accidental modification.
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.
✓
chmod 640 /etc/shadow; chattr +i /etc/shadow
Why this is correct
Sets permissions to owner rw, group r, others none; then sets immutable attribute.
Related concept
Read the scenario before looking for a memorised answer.
✗
chmod 640 /etc/shadow; chattr +a /etc/shadow
Why it's wrong here
chattr +a sets append-only, not immutable; the file can still be read.
✗
chmod 640 /etc/shadow; chmod +i /etc/shadow
Why it's wrong here
chmod +i is not a valid command; must use chattr.
✗
chmod 600 /etc/shadow; chattr +i /etc/shadow
Why it's wrong here
chmod 600 removes group read, so shadow group cannot read the file.
Common exam traps
Common exam trap: answer the scenario, not the keyword
CompTIA often tests the distinction between chmod (file permissions) and chattr (extended attributes), and the trap here is that candidates may confuse the immutable attribute (+i) with the append-only attribute (+a) or mistakenly use chmod to set it.
Trap categories for this question
Command / output trap
chmod +i is not a valid command; must use chattr.
Detailed technical explanation
How to think about this question
The /etc/shadow file stores password hashes and must be protected from unauthorized read access. The shadow group is a standard Linux group that allows certain system utilities (like passwd) to read the file without granting root privileges. The immutable attribute (+i) is a filesystem-level flag (ext2/3/4, xfs, etc.) that prevents any changes to the file's data or metadata, including renaming or deletion, and can only be set or removed by root (or a process with CAP_LINUX_IMMUTABLE). This is more restrictive than standard Unix permissions and is commonly used for critical system files.
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.
Security — This question tests Security — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: chmod 640 /etc/shadow; chattr +i /etc/shadow — Option A is correct because chmod 640 sets the file permissions to read/write for root (owner) and read-only for the shadow group, while removing all access for others. chattr +i sets the immutable attribute, which prevents any modifications (including deletion, renaming, or content changes) even by root until the attribute is removed. This satisfies the requirement that only root and the shadow group can read the file, and no one else can read it, while also protecting against accidental modification.
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.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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