  A dc current can be pumped through an interacting system by periodically
varying two independent parameters such as magnetic field and a gate potential.
We present a formula for the adiabatic pumping current in general interacting
systems, in terms of instantaneous properties of the system, and find the
limits for its applicability. This formula generalizes the scattering approach
for noninteracting pumps. We study the pumped spin in a system that exhibits
the two-channel Kondo effect as an application of the adiabatic pumping
formula. We find that a quantized spin of $\hbar$ is transferred between the
two channels as the temperature approaches zero, and discuss the non-Fermi
liquid features of this system at finite temperatures.
