[[Image:group-add.png|thumb|right|400px300px|When a file is created it is assigned an owner and a default (primary) group. The Linux system administrator can not only change a file's ownership, but also change the default group that file belongs to. In addition, the sysadmin can also add other users to a supplementary group that they have created via the '''usermod''' command. This is useful in setting "same group" permissions via the '''chmod''' command. ]]