We present coarse-grained molecular (many-body dissipative particle) dynamics simulations to unravel the wetting mechanism of spontaneous rise of a liquid thin film along vertical flat and rough surfaces. We show that the displacement of the rising contact line, in single- and double-wall geometry, exhibits a ballistic motion (similar to t) followed by a diffusive dynamics (similar to root t) during the rise of the liquid thin film against gravity. Dynamic contact angle decreases as the contact line transitions from ballistic to diffusive regime. Explicit analysis of the velocity and vorticity profile in the bulk and in the proximity of the contact line suggests an unsteady flow field behind the rising three-phase contact line. Furthermore, our simulation results indicate that contact line dynamics and the flow field behind the contact line are independent of the surface roughness.