Actually, a system is linear if it follows the two properties of linearity:

1) scaling. if y(t) = x(t), then Ay(t) = Ax(t) | If you scale your input by A, your output will also be scaled by A.
2) superposition. if y1(t) = x1(t) and y2(t) = x2(t), then y1(t) + y2(t) = x1(t) + x2(t) | If you add two inputs, your output will be a sum of them.

Yes, linear scaling means 100% scaling.