Это я не так понял :)
man gpasswd
SYNOPSIS
gpasswd group
gpasswd -a user group
gpasswd -d user group
gpasswd -R group
gpasswd -r group
gpasswd [-A user,...] [-M user,...] group
DESCRIPTION
gpasswd is used to administer the /etc/group file (and /etc/gshadow
file if compiled with SHADOWGRP defined). Every group can have adminis‐
trators, members and a password. System administrator can use -A option
to define group administrator(s) and -M option to define members and
has all rights of group administrators and members.