- A
useradd -G
Why wrong: useradd creates a new user; -G sets initial groups, but cannot be used on existing user.
- B
gpasswd -a
Adds user to a group.
- C
addgroup
Why wrong: addgroup is Debian-specific and does not take existing user as argument; it's for adding groups.
- D
groupmod
Why wrong: Modifies group properties, not membership.
- E
usermod -aG
Appends user to supplementary groups.
Question 110 of 513
LFCS User and Group Management Practice Question
This LFCS practice question tests your understanding of user and group management. 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 add an existing user to a supplementary group?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
gpasswd -a
The `gpasswd -a` command adds a user to a specified group, and `usermod -aG` appends a user to a supplementary group without removing them from other groups. Both commands modify the `/etc/group` file to include the user in the group's member list, making them correct for adding an existing user to a supplementary 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.
- ✗
useradd -G
Why it's wrong here
useradd creates a new user; -G sets initial groups, but cannot be used on existing user.
- ✓
gpasswd -a
Why this is correct
Adds user to a group.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
addgroup
Why it's wrong here
addgroup is Debian-specific and does not take existing user as argument; it's for adding groups.
- ✗
groupmod
Why it's wrong here
Modifies group properties, not membership.
- ✓
usermod -aG
Why this is correct
Appends user to supplementary groups.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse `usermod -G` (which replaces all supplementary groups) with `usermod -aG` (which appends), leading them to select `usermod -G` alone as correct, or they mistakenly think `useradd -G` can modify an existing user.
Detailed technical explanation
How to think about this question
Under the hood, both `gpasswd -a` and `usermod -aG` write the user's username to the group's entry in `/etc/group`, specifically in the comma-separated list of members in the fourth field. The `-a` flag in `usermod` is critical because omitting it causes `usermod -G` to replace the user's current supplementary group list with only the specified groups, potentially removing them from other groups. In real-world scenarios, using `usermod -G` without `-a` is a common mistake that can lock users out of necessary groups, such as `sudo` or `docker`.
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 LFCS 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.
- →
User and Group Management — study guide chapter
Learn the concepts, then practise the questions
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FAQ
Questions learners often ask
What does this LFCS question test?
User and Group Management — This question tests User and Group Management — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: gpasswd -a — The `gpasswd -a` command adds a user to a specified group, and `usermod -aG` appends a user to a supplementary group without removing them from other groups. Both commands modify the `/etc/group` file to include the user in the group's member list, making them correct for adding an existing user to a supplementary group.
What should I do if I get this LFCS 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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Last reviewed: Jul 4, 2026
This LFCS practice question is part of Courseiva's free Linux Foundation 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 LFCS exam.
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