Add

Add Groups

sudo groupadd <groupname>

Add user to group

sudo gpasswd --add <username> <groupname>

Short option

sudo gpasswd -a <username> <groupname>

Remove user from group

sudo gpasswd --delete <username> <groupname>

Short option

sudo gpasswd -d <username> <groupname>

Replace user login group

sudo usermod --gid <new_login_group> <username>

Short option

sudo usermod -g <new_login_group> <username>

Revert user login group

sudo usermod --gid <username> <username>

Short option

sudo usermod -g <username> <username>