Adding and Deleting Group Members

If you need to give users some group memberships, or delete some users from groups, edit /etc/groups manually. Just copy and paste; it’s the fastest way.

You may also use adduser and usermod, but beware of sneaky gotchas: adduser will only add a user to one group at a time, but usermod, which allows you to list several groups at once, will overwrite any existing group assignments.