Primary Group Membership Grants File Access Even When User Not Listed in /etc/group
This EX200 practice question tests your understanding of manage users and groups. 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.
Refer to the exhibit. A user bob exists with UID 1002 and GID 1002. The /etc/group shows a group bob with GID 1002 but no members listed. Bob tries to access a file owned by group 'bob' with permissions 640 and owner root. What will happen?
Bob will not be able to read the file because the group bob has no members.
Why wrong: This is incorrect. Even though the group 'bob' has no members listed in /etc/group, Bob's primary group (from /etc/passwd) is 'bob' with GID 1002, which matches the file's group owner. Therefore, he inherits the group read permission (r--) from the file's 640 permissions and can read the file.
B
Bob will be able to read the file because he is a member of the group bob.
Why wrong: This option is technically true (Bob can read the file), but the reasoning is incomplete. Bob is a member of the group 'bob' by virtue of his primary group assignment, not because he is listed in /etc/group. The correct answer (C) explicitly states that his primary group is 'bob', which is the precise reason.
C
Bob will be able to read the file if his primary group is bob, which it is.
This is correct. The file's permissions are 640, meaning owner (root) has read/write, group (bob) has read, and others have none. Bob's primary group is 'bob' (GID 1002), matching the file's group. Therefore, Bob has read access. This holds true regardless of whether he appears in /etc/group.
D
Bob will be able to read the file only if he is explicitly listed in /etc/group.
Why wrong: This is incorrect. Explicit listing in /etc/group is not required for group membership. The primary group from /etc/passwd is sufficient to grant group access.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Bob will be able to read the file if his primary group is bob, which it is.
Option C is correct because file access control in Linux uses the user's primary group (GID) from /etc/passwd for group ownership checks. Bob's primary group is 'bob' with GID 1002, which matches the file's group owner. The file has permissions 640 (owner root:rw-, group bob:r--, others:---), so Bob inherits read permission via his primary group membership, regardless of whether he is explicitly listed in /etc/group.
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.
✗
Bob will not be able to read the file because the group bob has no members.
Why it's wrong here
This is incorrect. Even though the group 'bob' has no members listed in /etc/group, Bob's primary group (from /etc/passwd) is 'bob' with GID 1002, which matches the file's group owner. Therefore, he inherits the group read permission (r--) from the file's 640 permissions and can read the file.
✗
Bob will be able to read the file because he is a member of the group bob.
Why it's wrong here
This option is technically true (Bob can read the file), but the reasoning is incomplete. Bob is a member of the group 'bob' by virtue of his primary group assignment, not because he is listed in /etc/group. The correct answer (C) explicitly states that his primary group is 'bob', which is the precise reason.
✓
Bob will be able to read the file if his primary group is bob, which it is.
Why this is correct
This is correct. The file's permissions are 640, meaning owner (root) has read/write, group (bob) has read, and others have none. Bob's primary group is 'bob' (GID 1002), matching the file's group. Therefore, Bob has read access. This holds true regardless of whether he appears in /etc/group.
Related concept
Read the scenario before looking for a memorised answer.
✗
Bob will be able to read the file only if he is explicitly listed in /etc/group.
Why it's wrong here
This is incorrect. Explicit listing in /etc/group is not required for group membership. The primary group from /etc/passwd is sufficient to grant group access.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Red Hat often tests the misconception that /etc/group member listings are the sole determinant of group membership, when in fact the primary GID from /etc/passwd always grants group access.
Detailed technical explanation
How to think about this question
Under the hood, the kernel checks the file's group ownership against the user's effective GID (EGID), which is set from the user's primary GID in /etc/passwd at login. The /etc/group member list is only relevant for supplementary groups (via the groups command or initgroups()), but primary group access is always granted. In real-world scenarios, this prevents accidental lockout when a user's primary group has no explicit members listed, ensuring consistent access to group-owned 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 EX200 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.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Manage users and groups — This question tests Manage users and groups — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Bob will be able to read the file if his primary group is bob, which it is. — Option C is correct because file access control in Linux uses the user's primary group (GID) from /etc/passwd for group ownership checks. Bob's primary group is 'bob' with GID 1002, which matches the file's group owner. The file has permissions 640 (owner root:rw-, group bob:r--, others:---), so Bob inherits read permission via his primary group membership, regardless of whether he is explicitly listed in /etc/group.
What should I do if I get this EX200 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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