Grid computing environments are being extended in order to present some features that are typically found in pervasive computing environments. In particular, Grid environments have to allow mobile users to access to their services and resources, and self-adapt based on mobile user location and context. Moreover, mobile users have to have the possibility of changing their location without wondering about their pending computations. This requires that the environment be able to self-manage mobile users implicit disconnections, who may also reappear later and be willing of resuming their computations. In this paper, we present a session manager service for distributed federations of pervasive grids. The service makes mobile users able of leaving a pervasive grid and resuming later, and even in another grid of the federation, their computations. The service relies on the mobile agents technology. In particular, a personal agent is associated to every mobile user active in the environment. The personal agent offers the list of application services available at the location of the user and handles the list of activated services. If the user moves in another grid, the personal agent migrates in the new grid, handles the list of pending services, and updates the list of available services for the new location.