Some device nodes are owned by the user whose session is active on the client, while others might be owned by root or by other users that had previously active sessions on the client. Device permissions, access controls and ownership rules are determined by the class of device. For serial devices, only the user whose session is active on the client or the superuser have permission to use the attached device. If no user has an active session, superuser owns the serial device nodes. This rule might not be applicable for other classes of USB devices connected to the client.