Which command adds an existing user to a specified group?

• A. usermod -G <group> <user>
• B. gpasswd -a <user> <group>
• C. adduser <user> <group>
• D. usermod -g <group> <user>

Answer: (A)

Modifying a user's group membership is what this is testing. Using the user management tool to assign a group directly attaches the user to that specified group. The command does this by listing the group with -G and naming the user, which is the straightforward way to grant access associated with that group.

Keep in mind that -G sets the user’s supplementary groups to exactly the ones you specify; if you want to preserve any existing supplementary groups while adding a new one, you would use the append form: -aG. That nuance is important for real-world administration.

Other options either use a different tool or target a different aspect of grouping: gpasswd -a also adds a user to a group but is a separate utility; adduser is typically for creating users; and setting the primary group with -g would change the main group, not merely add to the specified group.