[det]set_user_and_group(+User)
[det]set_user_and_group(+User,
+Group)Set the UID and GID to the User. User is either a
UID or a user name. If Group is not specified, the primary
group of User is used. If initgroups/2
is available, the resulting group access list of the calling process
consists of the registered groups for User and the specified Group.