We systematically study the self-assembled bulk cylinder-forming morphologies of an ABC star triblock copolymer melt confined in a cylindrical nanotube by applying real-space self-consistent mean-field theory. We observe a variety of novel structures that are not found in bulk, with pore constraints and selectivity. We vary the interaction parameters of the distinct three blocks with the cylindrical nanotubes from neutral to preferential for one block in a fixed order of nanotube diameter. As the confinement intensity and surface interaction increased, structural transition occurs, which is determined by free energy and analyzed by the internal energy and configuration entropy. In addition, the sequence of structure remarkably changes as the preferred surface and confinement are varied. We map the stability regions and phase diagrams for all of the structures.