gpasswd

Administer /etc/group and /etc/gshadow. More information: https://manned.org/gpasswd.

Define group administrators:

sudo gpasswd {{[-A|--administrators]}} {{user1,user2}} {{group}}

Set the list of group members:

sudo gpasswd {{[-M|--members]}} {{user1,user2}} {{group}}

Create a password for the named group:

gpasswd {{group}}

Add a user to the named group:

gpasswd {{[-a|--add]}} {{user}} {{group}}

Remove a user from the named group:

gpasswd {{[-d|--delete]}} {{user}} {{group}}