Quick Answer
The correct commands to change the primary group of an existing user are `usermod -g` and `gpasswd -a`. The `usermod -g` command directly sets a new primary group for the user by modifying the GID field in `/etc/passwd`, while `gpasswd -a` adds the user to a group but does not alter the primary group—it only affects supplementary membership, which is a common point of confusion. On the Red Hat Certified System Administrator EX200 exam, this distinction tests your understanding of group management fundamentals, often appearing in performance-based tasks where you must reconfigure user permissions without breaking existing access. A frequent trap is mistaking `usermod -aG` (which adds supplementary groups) for the primary group change; remember that the lowercase `-g` flag is the only one that modifies the primary group. For a quick memory tip: think "lowercase g for the group that gets the gold" (primary), and "uppercase G for the guest list" (supplementary).
This EX200 practice question tests your understanding of manage users and groups. 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 TWO commands can change the primary group of an existing user?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "primary"
Why it matters: Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
usermod -aG
The -aG option appends the user to specified supplementary groups.
gpasswd -a
gpasswd -a adds a user to a group.
vigr
Why wrong: vigr edits the group file, but not a command to add user to group directly.
groupmems -a
Why wrong: groupmems -a adds a user to a group but requires interactive mode; not as straightforward.
useradd -G
Why wrong: useradd -G sets supplementary groups during user creation, not for existing users.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
usermod -aG
The `usermod -g` command (not `-aG`, which adds supplementary groups) changes the primary group of an existing user. The `gpasswd -a` command adds a user to a group, but it does not change the primary group; it only affects supplementary group membership. Therefore, neither option A nor B is correct for changing the primary group. The correct commands are `usermod -g` (to set the primary group) and `usermod -G` (to set supplementary groups, but not the primary).
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.
usermod -aG
Why this is correct
The -aG option appends the user to specified supplementary groups.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
gpasswd -a
Why this is correct
gpasswd -a adds a user to a group.
Clue confirmation
The clue word "primary" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
vigr
Why it's wrong here
vigr edits the group file, but not a command to add user to group directly.
groupmems -a
Why it's wrong here
groupmems -a adds a user to a group but requires interactive mode; not as straightforward.
useradd -G
Why it's wrong here
useradd -G sets supplementary groups during user creation, not for existing users.
Common exam traps
The trap here is confusing the `-g` (primary group) and `-G` (supplementary groups) flags with `usermod`, and assuming `gpasswd -a` or `groupmems -a` can change the primary group when they only manage supplementary membership.
Trap categories for this question
Command / output trap
vigr edits the group file, but not a command to add user to group directly.
Detailed technical explanation
The primary group of a user is stored in the `/etc/passwd` file (the GID field), not in `/etc/group`. Changing it requires updating that field, which `usermod -g` does by modifying the GID in `/etc/passwd`. The `-g` flag accepts either a group name or GID, and the group must exist. A subtle behavior: if the user is the sole member of their current primary group, changing the primary group does not remove them from the old group; they remain as a supplementary member unless explicitly removed.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Manage users and groups — This question tests Manage users and groups — Read the scenario before looking for a memorised answer..
The correct answer is: usermod -aG — The `usermod -g` command (not `-aG`, which adds supplementary groups) changes the primary group of an existing user. The `gpasswd -a` command adds a user to a group, but it does not change the primary group; it only affects supplementary group membership. Therefore, neither option A nor B is correct for changing the primary group. The correct commands are `usermod -g` (to set the primary group) and `usermod -G` (to set supplementary groups, but not the primary).
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Yes — watch for: "primary". Asks for the main purpose or function, not a secondary benefit. Eliminate answers that describe side-effects or partial functions.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 11, 2026
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