We have applied the thermodynamics of irreversible processes to grain boundary electromigration and creep at moderated temperatures in fine-grained thin film lines. In response to the forces of electrical field and mechanical stress, atomic motion in the lines occurs via two kinds of kinetic paths; lattice diffusion and grain boundary diffusion. The extreme cases, where each of them becomes dominant, have been analyzed. We show that the effective charge number of grain boundary electromigration can be determined by measuring the back-stress in a fine-grained short line. In the reverse case the back-stress can be measured from the electromigration damage. The deformation potential due to grain boundary creep is negligible according to Onsager's reciprocity relation.