The account alice already belongs to the supplementary groups audio and video. You must additionally put her in the group developers while keeping her existing memberships. Which command does that?
LPIC-1 Exam 102-500, objective 107. Administrative tasks medium
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The options
Not correct usermod -G developers alice
Wrong, and destructive. Without -a, -G replaces the entire list of supplementary groups. alice would come out of this belonging only to developers, silently losing audio and video.
Correct usermod -aG developers alice
Correct. -a (append) is only meaningful together with -G, and it adds the named group or groups to the user's existing supplementary group list instead of replacing it.
Not correct usermod -g developers alice
Wrong. Lowercase -g sets the user's primary group, rewriting the GID field in /etc/passwd. Her supplementary groups are untouched but her primary group changes, which is not what was asked.
Not correct groupmod -a alice developers
Wrong. groupmod changes properties of a group itself (its name with -n, its GID with -g). It has no -a option and does not manage membership.
Why
Supplementary membership lives in the fourth field of /etc/group. `usermod -aG` appends; `usermod -G` overwrites. The missing -a is one of the classic ways to lock an administrator out of sudo on a Debian or Ubuntu box, because it drops the account from the sudo group. `gpasswd -a alice developers` is the safe alternative that only ever adds.
Where this comes from
- Cited
- LPI exam objective 107.1
- What it says
- Add, modify and remove users and groups and manage their group memberships.
Practise this
Reading one question is not practice. The trainer will draw a set from objective 107 and space the ones you get wrong.