A linear drive for a vehicle occupant restraint system, especially for a belt buckle tensioner, comprises a cylinder, a piston that can be moved in the cylinder and that has a locking part that is firmly connected to a traction element, and comprising at least one locking member that is arranged movably between the locking part and the inner wall of the cylinder. The locking part has at least one obliquely disposed clamping surface that is arranged in such a way that, when the traction element makes a pushing movement, the clamping surface clamps the locking member between the locking part and the cylinder.