In this paper, we propose a distributed primal-dual algorithm for computation of a generalized Nash equilibrium (GNE) in noncooperative games over network systems. In the considered game, not only each player's local objective function depends on other players' decisions, but also the feasible decision sets of all the players are coupled together with a globally shared affine inequality constraint. Adopting the variational GNE, that is the solution of a variational inequality, as a refinement of GNE, we introduce a primal-dual algorithm that players can use to seek it in a distributed manner. Each player only needs to know its local objective function, local feasible set, and a local block of the affine constraint. Meanwhile, each player only needs to observe the decisions on which its local objective function explicitly depends through the interference graph and share information related to multipliers with its neighbors through a multiplier graph. Through a primal-dual analysis and an augmentation of variables, we reformulate the problem as finding the zeros of a sum of monotone operators. Our distributed primal-dual algorithm is based on forward-backward operator splitting methods. We prove its convergence to the variational GNE for fixed step-sizes under some mild assumptions. Then a distributed algorithm with inertia is also introduced and analyzed for variational GNE seeking. Finally, numerical simulations for network Cournot competition are given to illustrate the algorithm efficiency and performance.Engineering network systems, like power grids, communication networks, transportation networks and sensor networks, play a foundation role in modern society. The efficient and secure operation of various network systems relies on efficiently solving decision and control problems arising in those large scale network systems. In many decision problems, the nodes can be regarded as agents that need to make local decisions possibly limited by the shared network resources within local feasible sets. Meanwhile, each agent has a local cost/utility function to be optimized, which depends on the decisions of other agents. The traditional manner for solving such decision problems over networks is the centralized optimization approach, which relies on a control center to gather the data of the problem and to optimize the social welfare (usually taking the form of the sum of local objective functions) within the local and global constraints. The centralized optimization approach may not be suitable for decision problems over large scale networks, since it needs bidirectional communication between all the network nodes and the control center, it is not robust to the failure of the center node, and the computational burden for the center is unbearable. It is also not preferable because the privacy of each agent might be compromised when the data is transferred $