Use sg
.
Por exemplo, o comando a seguir invocará sleep
para o grupo group-name
sg group-name -c 'sleep 100'
Da página do manual:
NAME
sg - execute command as different group ID
SYNOPSIS
sg [-] [group [-c ] command]
DESCRIPTION
The sg command works similar to newgrp but accepts a command. The
command will be executed with the /bin/sh shell...